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Prevalence of epilepsy among people with intellectual disabilities: A systematic review

Open ArchivePublished:March 30, 2015DOI:https://doi.org/10.1016/j.seizure.2015.03.016

      Highlights

      • Review of 48 studies on prevalence in people with intellectual disabilities.
      • Pooled estimate 22.2% (95% CI 19.6–25.1) for general samples.
      • Prevalence increased with increasing level of intellectual disability.
      • Pooled estimate 12.4% (95% CI 9.1–16.7) for people with Down syndrome.
      • Prevalence increased with age in people with Down syndrome.

      Abstract

      Purpose

      Epilepsy is more common in people with intellectual disabilities than in the general population. However, reported prevalence rates vary widely between studies. This systematic review aimed to provide a summary of prevalence studies and estimates of prevalence based on meta-analyses.

      Method

      Studies were identified via electronic searches using Medline, Cinahl and PsycINFO and cross-citations. Information extracted from studies was tabulated. Prevalence rate estimates were pooled using random effects meta-analyses and subgroup analyses were conducted.

      Results

      A total of 48 studies were included in the tabulation and 46 studies were included in meta-analyses. In general samples of people with intellectual disabilities, the pooled estimate from 38 studies was 22.2% (95% CI 19.6–25.1). Prevalence increased with increasing level of intellectual disability. For samples of people with Down syndrome, the pooled estimate from data in 13 studies was 12.4% (95% CI 9.1–16.7), decreasing to 10.3% (95% CI 8.4–12.6) following removal of two studies focusing on older people. Prevalence increased with age in people with Down syndrome and was particularly prevalent in those with Alzheimer's/dementia.

      Conclusion

      Epilepsy is highly prevalent in people with intellectual disabilities. Services must be equipped with the skills and information needed to manage this condition.

      Keywords

      1. Introduction

      Intellectual disability (often referred to as ‘learning disabilities’ in the United Kingdom) refers to a significant general impairment in intellectual functioning that is acquired during childhood, typically operationalised as scoring more than two standard deviations below the population mean on a test of general intelligence [
      • Einfeld S.
      • Emerson E.
      Intellectual disability.
      ]. While estimates of the prevalence of intellectual disability vary widely, it has been estimated that approximately 2% of the adult population have intellectual disability [
      • Maulik P.K.
      • Mascarenhas M.N.
      • Mathers C.D.
      • Dua T.
      • Saxena S.
      Prevalence of intellectual disability: a meta-analysis of population-based studies.
      ,
      • Hatton C.
      • Emerson E.
      • Glover G.
      • Robertson J.
      • Baines S.
      • Christie A.
      People with learning disabilities in England 2013.
      ].
      In the general population, estimates of the prevalence of epilepsy are in region of 0.6% [
      • Forsgren L.
      • Beghi E.
      • Öun A.
      • Sillanpää M.
      The epidemiology of epilepsy in Europe – a systematic review.
      ,
      • Ngugi A.K.
      • Bottomley C.
      • Kleinschmidt I.
      • Sander J.W.
      • Newton C.R.
      Estimation of the burden of active and life-time epilepsy: a meta-analytic approach.
      ] to 1% [
      • Linehan C.
      • Kerr M.P.
      • Walsh P.N.
      • Brady G.
      • Kelleher C.
      • Delanty N.
      • et al.
      Examining the prevalence of epilepsy and delivery of epilepsy care in Ireland.
      ,
      • Joint Epilepsy Council
      Epilepsy prevalence, incidence and other statistics.
      ]. In people with intellectual disabilities, estimates of the prevalence of epilepsy vary due to differences in the methods used and inherent population biases [
      • Lhatoo S.D.
      • Sander J.W.
      The epidemiology of epilepsy and learning disability.
      ]. Reported rates range, for example, from 16.1% of 1595 people with intellectual disabilities identified in South Wales [
      • Morgan C.L.I.
      • Baxter H.
      • Kerr M.P.
      Prevalence of epilepsy and associated health service utilization and mortality among patients with intellectual disability.
      ] to 30.7% in a random sample of 753 people with intellectual disabilities aged 40 or more from Ireland's National Intellectual Disability Database (NIDD) [
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.
      ]. In a systematic review of the prevalence of chronic health conditions in children with intellectual disabilities, the most common condition was epilepsy [
      • Oeseburg B.
      • Dijkstra G.J.
      • Groothoff J.W.
      • Reijneveld S.A.
      • Jansen D.E.M.C.
      Prevalence of chronic health conditions in children with intellectual disability: a systematic literature review.
      ] with prevalence rates in the 14 studies identified ranging from 5.5% to 35.0%, with an overall weighted mean prevalence rate of 22.0% (95% CI 20.8–23.2).
      Despite variation in reported prevalence figures, it is clear that the prevalence of epilepsy in people with intellectual disabilities is much greater than in the general population. Further, for people with intellectual disabilities and epilepsy, co-morbidities may be common. Over half of a representative sample of children with intellectual disability and active epilepsy were reported to have a psychiatric diagnosis [
      • Steffenburg S.
      • Gillberg C.
      • Steffenburg U.
      Psychiatric disorders in children and adolescents with mental retardation and active epilepsy.
      ]. However, conflicting findings exist and there is no consensus as to whether people with both intellectual disability and epilepsy are at increased risk of psychiatric morbidity compared to their peers with either epilepsy or intellectual disability alone [
      • Beavis J.
      • Kerr M.
      • Marson Anthony G.
      • Dojcinov I.
      Pharmacological interventions for epilepsy in people with intellectual disabilities.
      ].
      The prevalence of epilepsy also increases with increasing severity of intellectual disabilities. In the Oeseburg et al. [
      • Oeseburg B.
      • Dijkstra G.J.
      • Groothoff J.W.
      • Reijneveld S.A.
      • Jansen D.E.M.C.
      Prevalence of chronic health conditions in children with intellectual disability: a systematic literature review.
      ] review, the lower rate of 5.5% was for children with borderline to moderate intellectual disability [
      • Dekker M.C.
      • Koot H.M.
      DSM-IV disorders in children with borderline to moderate intellectual disability. I: prevalence and impact.
      ], whilst the rate of 35.0% was for children with mild to profound intellectual disability [
      • Koskentausta T.
      • Iivanainen M.
      • Almqvist F.
      Psychiatric disorders in children with intellectual disability.
      ]. Such wide differences highlight the need to examine prevalence rates taking into account factors such as the degree of intellectual disability of the sample. Samples based on, for example, those in contact with intellectual disability services are likely to miss out some people with less severe intellectual disabilities. A further issue is that the ascertainment of epilepsy is not consistent across studies, both in terms of the definition of epilepsy used, and how the information is collected.
      The aim of this review is to summarise existing research on the prevalence of epilepsy in people with intellectual disabilities, including studies relating specifically to people with Down syndrome which is the most common genetic cause of intellectual disabilities [
      • Sherman S.L.
      • Allen E.G.
      • Bean L.H.
      • Freeman S.B.
      Epidemiology of Down syndrome.
      ]. The review also aims to provide pooled prevalence estimates for studies taking into account factors such as age and level of intellectual disability. Whilst existing reviews have considered the prevalence of epilepsy in people with intellectual disabilities, these reviews do not cover more recent studies on prevalence that now provide more data, particularly in relation to adults with intellectual disabilities. As highlighted in one earlier review, adults have previously been underrepresented in research on the epidemiology of epilepsy in people with intellectual disabilities, with the vast majority of published data pertaining to children [
      • Lhatoo S.D.
      • Sander J.W.
      The epidemiology of epilepsy and learning disability.
      ]. As this review aims to estimate epilepsy prevalence in the general population of people with intellectual disabilities or Down syndrome, it does not include studies relating to less common specific genetic conditions associated with intellectual disabilities, although it is evident that work on such conditions has been published [
      • Leung H.T.T.
      • Ring H.
      Epilepsy in four genetically determined syndromes of intellectual disability.
      ].

      2. Method

      Electronic literature database searches were conducted in Medline, Cinahl and PsycINFO on EBSCO. In addition, the reference lists of articles meeting the inclusion criteria were searched. The reference lists of key book chapters were also searched [
      • Blake P.
      • Kerr M.
      Epilepsy.
      ,
      • Brown S.
      Epidemiology of epilepsy in persons with intellectual disabilities.
      ,
      • Cardoza B.
      • Kerr M.
      Diseases of the nervous system. I: epilepsy, hydrocephalus and nervous system malformations.
      ]. Searches were completed on 19 June 2014. Searches included terms relating to both prevalence and mortality to create a pool of articles on prevalence or mortality, with articles on mortality being retained for a separate review. Searches combined terms for epilepsy, intellectual disabilities, and prevalence/mortality with the Boolean operator ‘and’. Full details of the search terms are given in Appendix A.

      2.1 Inclusion criteria

      • Peer reviewed
      • English Language full text
      • Published from 1990
      • Primary research
      • Present exact figures on the prevalence of epilepsy
      • Samples where 50% or more have intellectual disabilities or mixed samples where results are disaggregated for people with intellectual disabilities
      • Studies using representative samples of people with intellectual disabilities or samples representative of specific sub-groups of people with intellectual disabilities (e.g. specific level of intellectual disability, specific age band)

      2.2 Exclusion criteria

      • Case studies
      • Case series
      • Reviews
      • Studies based on neonates (new born infants up to 28 days after birth)
      • Studies on conditions where intellectual disabilities cannot be assumed (e.g. cerebral palsy) where results not disaggregated for people with intellectual disabilities
      • Studies on specific syndromes associated with intellectual disabilities with the exception of Down syndrome
      • Studies where ascertainment of epilepsy could be confounded with febrile seizures
      • Studies employing samples unrepresentative of specific sub-groups of people with intellectual disability e.g. only those attending for inpatient specialist medical care
      • Studies not presenting exact figures
      Initially, titles and abstracts were used to exclude those studies which were obviously not within the scope of reviews on prevalence or mortality. Those retained for further screening were those for which relevance could not be assessed without accessing full text, or those that were chosen as potentially within scope. These studies were screened by the first and second author and discussed until consensus was reached on whether or not they met the inclusion criteria. Those relevant to other future planned reviews (e.g. mortality) were filed for future reference.
      Where multiple articles used the same sample or samples were likely to have considerable overlap, only the most recent study was included. One exception was a study based on adults with intellectual disabilities registered with the Leicestershire Intellectual Disability Register for the period 1993–2010 which reported a prevalence of 19.1% in a sample of 5391 [
      • Kiani R.
      • Tyrer F.
      • Jesu A.
      • Bhaumik S.
      • Gangavati S.
      • Walker G.
      • et al.
      Mortality from sudden unexpected death in epilepsy (SUDEP) in a cohort of adults with intellectual disability.
      ]. As this study focuses on sudden and unexpected death in epilepsy (SUDEP), it does not outline the methodology for obtaining this estimate. As such, it was decided to include an earlier study based on the same register which focused on epilepsy prevalence [
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.
      ]. A further study including only people with Down syndrome which was partly based on the Leicestershire Intellectual Disability Register was also included [
      • Collacott R.A.
      Epilepsy, dementia and adaptive behaviour in Down's syndrome.
      ].
      Information from the included studies was extracted by the first author and this information was tabulated (see Table 1).
      Table 1Summary of included studies giving prevalence rates for epilepsy in people with intellectual disabilities. Figures under male, and levels of ID columns relate to characteristics of the study sample. Sorted by author name. Studies only looking at Down syndrome listed separately at end of table.
      Authors, year and quality score
      Presented as Total score (epilepsy definition score/ascertainment of epilepsy score/subgroup analysis score).
      Country of studyKey sample featuresSample sourceAge range (mean (SD); median)Male %Borderline ID %Mild ID %Moderate ID %Severe ID %Profound ID %Unspecified ID %
      Airaksinen et al. (2000)
      • Airaksinen E.M.
      • Matilainen R.
      • Mononen T.
      • Mustonen K.
      • Partanen J.
      • Jokela V.
      • et al.
      A population-based study on epilepsy in mentally retarded children.


      10 (2/4/4)
      Finland (Kuopio Province)Children with ID born 1969–1972 in one province followed until age 22. CP 11%. LS ns.School achievement tests and social services registerPrevalence at age 22 yrs given55
      Calculated from available figures not reported directly.
      49
      Calculated from available figures not reported directly.
      51
      Calculated from available figures not reported directly.
      ←, included in previous figure; →, included in next figure.
      Arvio and Sillanpää (2003)
      • Arvio M.
      • Sillanpää M.
      Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.


      4 (0/3/1)
      FinlandPeople with SPID. DS 14.3%, AE 19.3%, FXS 3.9%. LS nsRegister of District Centre for ID (all in catchment)1–72 (ns; ns)ns52.547.5
      Benassi et al. (1990)
      • Benassi G.
      • Guarino M.
      • Cammarata S.
      • Cristoni P.
      • Fantini M.P.
      • Ancona A.
      • et al.
      An epidemiological study on severe mental retardation among schoolchildren in Bologna, Italy.


      3 (0/3/0)
      ItalyChildren with ‘severe’ ID (IQ ≤ 50). DS 22.2%. LS ns.System recording all school age children with ID3–13 (ns; ns)63.3100
      Christianson et al. (2002)
      • Christianson A.L.
      • Zwane M.E.
      • Manga P.
      • Rosen E.
      • Venter A.
      • Downs D.
      • et al.
      Children with intellectual disability in rural South Africa: prevalence and associated disability.


      3 (0/2/1)
      South AfricaChildren with ID in rural households, up to IQ 80. DS 2.1%, CP 8.4%Rural villages2–9 (ns; ns)61.3
      Calculated from available figures not reported directly.
      81.9
      Calculated from available figures not reported directly.
      18.1
      Calculated from available figures not reported directly.
      David et al. (2014)
      • David M.
      • Dieterich K.
      • de Villemeur A.B.
      • Jouk P.S.
      • Counillon J.
      • Larroque B.
      • et al.
      Prevalence and characteristics of children with mild intellectual disability in a French county.


      4 (0/3/1)
      France (Isère)Children with mild ID born 1997 living in one county in 2008. LS nsMaisons Départementales des Personnes Handicapées (MDPH) and Dept of Education9–13
      Calculated from available figures not reported directly.
      (ns; ns)
      ns100
      Dekker and Koot (2003)
      • Dekker M.C.
      • Koot H.M.
      DSM-IV disorders in children with borderline to moderate intellectual disability. I: prevalence and impact.


      2 (0/2/0)
      NetherlandsChildren with borderline to moderate ID living in family home. DS 5.3%Schools for ID7–20 (12.9 (3.0); ns)61.8100
      Fernell (1998)
      • Fernell E.
      Aetiological factors and prevalence of severe mental retardation in children in a Swedish municipality: the possible role of consanguinity.


      3 (0/3/0)
      SwedenChildren with ‘severe’ ID (IQ < 50–55). CP 23.4%, DS 20.3%. LS nsRegister of Board for Provision of Services to the Mentally Retarded BPSMR): all in one municipality3–16 (ns; ns)62.5100
      Forsgren et al. (1990)
      • Forsgren L.
      • Edvinsson S.O.
      • Blomquist H.K.
      • Heijbel J.
      • Sidenvall R.
      Epilepsy in a population of mentally retarded children and adults.


      8 (2/2/4)
      SwedenAll adults and children with ID in one County on a prevalence day. DS 13.7%, Fragile X 2.3%, RS 0.3%. LS anyRegister of BPSMR, neurology and paediatric departmentsAll (ns)nsnsnsnsnsns100
      Gittins and Rose (2008)
      • Gittins D.
      • Rose N.
      An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.


      5 (1/3/1)
      England, West MidlandsAdults with PMLD in one health district. LS family home, residential care, family placementSpecial needs register of LD service, CLDTs18–51+ (37 (ns); ns)ns100
      Goulden et al. (1991)
      • Goulden K.J.
      • Shinnar S.
      • Koller H.
      • Katz M.
      • Richardson S.A.
      Epilepsy in children with mental retardation: a cohort study.


      9 (2/3/4)
      Scotland, AberdeenChildren with ID born 1951–1955 followed to age 22. CP 14.9%, DS 5.1%. LS nsReceiving special services for ID prior to leaving schoolPrevalence figure given is for age 22ns78.6
      Calculated from available figures not reported directly.
      21.4
      Calculated from available figures not reported directly.
      Hand and Reid (1996)
      • Hand J.E.
      • Reid P.M.
      Older adults with lifelong intellectual handicap in New Zealand: prevalence, disabilities and implications for regional health authorities.


      1 (0/1/0)
      New Zealand (NZ)All NZ older adults with ID born before 1940, CP 4%, DS 13%. LS anyMultiple agencies and local networking51–88 (ns; ns)50.04.034.538.315.45.12.7
      Haveman et al. (2011)
      • Haveman M.
      • Perry J.
      • Salvador-Carulla L.
      • Walsh P.N.
      • Kerr M.
      • Van Schrojenstein Lantman-de Valk H.
      • et al.
      Ageing and health status in adults with intellectual disabilities: results of the European POMONA II study.


      4 (1/2/1)
      14 European countries (1 of which upper middle income)Adults with ID living in Europe. LS anyMainly service provider registers19–90 (41 (ns); ns)50.622.728.220.711.816.6
      Hove and Havik (2010)
      • Hove O.
      • Havik O.E.
      Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.


      1 (0/1/0)
      NorwayAdults with ID living in community. DS 16.4%, CP 9.1%. LS includes psychiatric wards if part of community care programmeSocial services18–97 (41.8 (14.5); ns)53.121.641.018.013.06.4
      Jelliffe-Pawlowski et al. (2003)
      • Jelliffe-Pawlowski L.L.
      • Shaw G.M.
      • Nelson V.
      • Harris J.A.
      Risk of mental retardation among children born with birth defects.


      5 (1/3/1)
      USChildren with ID from a larger cohort born with or without birth defects. CP 46.8%. LS nsID those receiving services from California Department of Developmental Services7–9 (ns; ns)ns52.747.3
      Koskentausta et al. (2002)
      • Koskentausta T.
      • Iivanainen M.
      • Almqvist F.
      Psychiatric disorders in children with intellectual disability.


      4 (0/3/1)
      FinlandAll children with ID born 1982 to 1988 in one district. LS mostly parental homePatient register of Rehabilitation Centre, hospitals, special schools6–13 (9.7 (ns); ns)59.456.119.411.612.9
      Lakhan (2013)
      • Lakhan R.
      Intelligence quotient is associated with epilepsy in children with intellectual disability in India.


      7 (0/4/3)
      IndiaChildren with ID living in village households in one of poorest districts. DS 7.3%, CP 31.3%Door to door survey in 63 villages3–18 (ns; ns)52.71.930.238.224.05.7
      Lewis et al. (2000)
      • Lewis J.N.
      • Tonge B.J.
      • Mowat D.R.
      • Einfeld S.L.
      • Siddons H.M.
      • Rees V.W.
      Epilepsy and associated psychopathology in young people with intellectual disability.


      (2000)

      3 (1/2/0)
      AustraliaYoung people with ID, LS anyServices in five districts of New South Wales8–22 (ns; ns)52.029.8
      Calculated from available figures not reported directly.
      40.8
      Calculated from available figures not reported directly.
      24.2
      Calculated from available figures not reported directly.
      5.1
      Calculated from available figures not reported directly.
      Lin et al. (2003)
      • Lin J.-D.
      • Wu J.L.
      • Lee P.N.
      Healthcare needs of people with intellectual disability in institutions in Taiwan: outpatient care utilization and implications.


      1 (0/1/0)
      TaiwanPeople with ID registered with day-care institutions, 92.6% age <26. LS nsCommunity-based day-care institutions1–26+ (13.7 (ns); ns)61.24.917.440.924.9
      Matthews et al. (2008)
      • Matthews T.
      • Weston N.
      • Baxter H.
      • Felce D.
      • Kerr M.
      A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.


      3 (1/2/0)
      WalesAdults with ID registered with GP. LS independent 10%, family home 46%, staffed home 44%40 general practices17–86 (41 (ns); ns)44nsnsnsnsns100
      McBrien and Macken (2009)
      • McBrien J.
      • Macken S.
      Meeting the health care needs of school-age children with intellectual disability.


      3 (0/3/0)
      IrelandChildren with moderate, to profound ID. Any chromosonal or genetic cause 48.5%, DS 24.7%. LS nsCentre providing educational and health services for all individuals with moderate, severe and profound ID in one area5–19 (ns; 12)66.064.935.1
      McCarron et al. (2014)
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.


      6 (1/2/3)
      IrelandOlder adults with ID, 3.1% with DS and dementia. LS allNational database (all ID eligible to receive services)40–65+ (54.8 (9.6); ns)452446245
      McDermott et al. (2005)
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.


      6 (2/3/1)
      USAdults with ID receiving primary health care. CP 24.9%, DS 8.9%. LS nsLarge urban or small rural primary care practice20–60+ age
      entry age includes those without ID in main study
      mean 36.5 (13.9); ns)
      52.0
      Calculated from available figures not reported directly.
      35.922.941.2
      McGrother et al. (2006)
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.


      6 (1/2/3)
      England, Leicester-shireAdults with ID known to services. LS anyLeicestershire LD Register20–70+ (ns; ns)56.6nsnsnsnsns100
      Memisevic and Sinanovic (2009)
      • Memisevic H.
      • Sinanovic O.
      Epilepsy in children with intellectual disability in Bosnia and Herzegovina: effects of sex, level and etiology of intellectual disability.


      7 (1/3/3)
      Bosnia and Herze-govina, SarajevoChildren with moderate or mild ID. Organic brain injury 21.0%, DS 20.4%, other genetic syndromes 13.2%. LS nsTwo special schools7–15 (ns; ns)62.9
      Calculated from available figures not reported directly.
      50.949.1
      Molteno et al. (2001)
      • Molteno G.
      • Molteno C.D.
      • Finchilescu G.
      • Dawes A.R.L.
      Behavioural and emotional problems in children with intellectual disability attending special schools in Cape Town, South Africa.


      1 (0/1/0)
      South Africa, Cape TownChildren with ID at special schools. CP 33.8%. LS nsTwo special schools and a training centre6–18 (ns; ns)55.535.838.613.810.71.1
      Morgan et al. (2003)
      • Morgan C.L.I.
      • Baxter H.
      • Kerr M.P.
      Prevalence of epilepsy and associated health service utilization and mortality among patients with intellectual disability.


      7 (1/3/3)
      WalesPeople with ID mainly age 16+ in contact with health or social services. LS anySocial services register, inpatient and outpatient databases, MH hospital dataset15–85+ (ns; ns)nsnsnsnsnsns100
      Murphy et al. (1995)
      • Murphy C.C.
      • Yeargin-Allsopp M.
      • Decouflé P.
      • Drews C.D.
      The administrative prevalence of mental retardation in 10-year-old children in metropolitan Atlanta, 1985 through 1987.


      4 (0/3/1)
      USChildren with ID born 1975 to 1977 living in study area at age 10. CP 12.3%. LS nsSchools, hospitals, other health and social services10 year olds59.269.930.1
      Nordin and Gillberg (1996)
      • Nordin V.
      • Gillberg C.
      Autism spectrum disorders in children with physical or mental disability or both. I. Clinical and epidemiological aspects.


      6 (2/4/0)
      SwedenAll children with ID born 1974 to 1988 in one region. CP 8.9%, DS 8.9%. LS nsHabilitation and educational services3–18 (ns; ns)63.4
      Calculated from available figures not reported directly.
      56.443.6
      Pawar and Akuffo (2008)
      • Pawar D.G.
      • Akuffo E.O.
      Comparative survey of comorbidities in people with learning disability with and without epilepsy.


      7 (1/3/3)
      England, London Borough of Waltham ForestAdults with ID in contact with services. LS residential homes, supported living, private homesAdults in contact with one CLDT (active cases)17–65+ (ns; ns)53.7nsnsnsnsns100
      Schieve et al. (2009)
      • Schieve L.A.
      • Boulet S.L.
      • Boyle C.
      • Rasmussen S.A.
      • Schendel D.
      Health of children 3 to 17 years of age with Down syndrome in the 1997–2005 national health interview survey.


      4 (1/2/1)
      USChildren in households with DS or with ID without DS. DS 19.5%National survey of households3–17 (ns; ns)59.6
      Calculated from available figures not reported directly.
      nsnsnsnsns100
      Schieve et al. (2012)
      • Schieve L.A.
      • Gonzalez V.
      • Boulet S.L.
      • Visser S.N.
      • Rice C.E.
      • Van Naarden Braun K.
      • et al.
      Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.


      3 (1/2/0)
      USChildren in households with ID without autismNational survey of households3–17 (ns; ns)58.1nsnsnsnsns100
      Steffenburg et al. (1995)
      • Steffenburg U.
      • Hagberg G.
      • Viggedal G.
      • Kyllerman M.
      Active epilepsy in mentally retarded children. I. Prevalence and additional neuro-impairments.


      6 (2/3/1)
      SwedenChildren with ID in one city born 1975–1986. CP 15.3%. LS nsEducation, inpatient, outpatient, child habilitation clinic and child neuropsychiatric clinic registers6–13 (ns; ns)ns63.037.0
      Strømme and Hagberg (2000)
      • Strømme P.
      • Hagberg G.
      Aetiology in severe and mild mental retardation: a population based study of Norwegian children.


      7 (2/4/1)
      NorwayChildren with mild or ‘severe’ ID (IQ < 50 assumed mod/sev/pro). Genetic cause 35%, CP 14%. LS nsMultiple sources (education and medical) used to identify all in one County8–13 (ns; ns)57.855.644.4
      Temtamy et al. (1994)
      • Temtamy S.A.
      • Kandil M.R.
      • Demerdash A.M.
      • Hassan W.A.
      • Meguid N.A.
      • Afifi H.H.
      An epidemiological/genetic study of mental subnormality in Assiut Governorate, Egypt.


      4 (0/4/0)
      EgyptChildren with ID in households. DS 2.6%, MCA 24.1%, primary CNS defect 12.9%Households in three localities in Egypt2–18 (ns; ns)68.130.8
      Calculated from available figures not reported directly.
      47.9
      Calculated from available figures not reported directly.
      21.4
      Calculated from available figures not reported directly.
      Tenenbaum et al. (2012)
      • Tenenbaum A.
      • Fuchs B.S.
      • Raskas M.
      • Carmeli E.
      • Aspler S.
      • Merrick J.
      National survey 2009 on medical services for persons with intellectual disability in residential care in Israel.


      1 (0/1/0)
      IsraelAll with ID living in residential centres. DS 8.1%, Fragile X 1.0%, Rett syndrome 0.2%Residential care centres0–60+ (ns; ns)56.313.341.131.613.40.6
      van Schrojenstein Lantman-de Valk et al. (2000)
      • van Schrojenstein Lantman-De Valk H.M.J.
      • Metsemakers J.F.M.
      • Haveman M.J.
      • Crebolder H.F.J.M.
      Health problems in people with intellectual disability in general practice: a comparative study.


      4 (1/3/0)
      NetherlandsAny general practice patients with ID. LS nsRegistration Network Family Practices (RNH) of Maastricht Universityns. 20% aged over 50, includes children62nsnsnsnsns100
      van Schrojenstein Lantman-de Valk et al. (1997)
      • van Schrojenstein Lantman-de Valk H.M.
      • van den Akker M.
      • Maaskant M.A.
      • Haveman M.J.
      • Urlings H.F.
      • Kessels A.G.
      • et al.
      Prevalence and incidence of health problems in people with intellectual disability.


      4 (0/1/3)
      NetherlandsPeople with ID in institutions or group homes. CP 11.8%, dementia 3.8%, DS 22.3%Institutions and group homes0–70+ (ns; ns)nsnsnsnsnsns100
      Wellesley et al. (1992)
      • Wellesley D.G.
      • Hockey K.A.
      • Montgomery P.D.
      • Stanley F.J.
      Prevalence of intellectual handicap in Western Australia: a community study.


      7 (2/3/2)
      AustraliaChildren in Western Australia with ID born 1967–1976. CP 19.8%. LS nsMultiple services and schools6–16 (ns; ns)59.6
      Calculated from available figures not reported directly.
      38.5
      Calculated from available figures not reported directly.
      31.0
      Calculated from available figures not reported directly.
      12.6
      Calculated from available figures not reported directly.
      7.1
      Calculated from available figures not reported directly.
      10.7
      Calculated from available figures not reported directly.
      Wong (2011)
      • Wong C.W.
      Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.


      5 (1/1/3)
      Hong KongAdults with ID in residential care. DS 13.2%, CP 16.7%Residential care services18–79 (44 (ns); ns)53.34.941.851.9
      Yousef (1995)
      • Yousef J.M.S.
      Epilepsy in a sample of children with intellectual disability in Jordan.


      6 (0/3/3)
      JordanChildren at special schools for ID. LS nsSpecial education centres in one Cityns; school age73.827.244.228.6
      Down syndrome studies
      Collacott (1993)
      • Collacott R.A.
      Epilepsy, dementia and adaptive behaviour in Down's syndrome.


      7 (2/3/2)
      England, Leicester-shireAdults with DS, dementia 5.1%. LS anyLeicestershire LD Register, health service records, day centres, residential services<30–60+ (ns; ns)nsnsnsnsnsns100
      Johannsen et al. (1996)
      • Johannsen P.
      • Christensen J.E.J.
      • Goldstein H.
      • Nielsen V.K.
      • Mai J.
      Epilepsy in Down syndrome: prevalence in three age groups.


      7 (2/4/1)
      DenmarkDS in age groups 14–16, 23–29 and 50–60. LS nsAll in one County identified via Danish register and city councilsAge groups 14–16, 23–29, 50–6062.5nsnsnsnsns100
      McCarron et al. (2005)
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.


      4 (0/3/1)
      IrelandAdults with DS aged 35+ in out-of-home placements, AD 50.8%Care settings (out-of-home placements)>35-ns (AD 55.4 (7.0); ns. Non-AD 50.8 (5.8); ns)33.969.430.6
      McVicker et al. (1994)
      • McVicker R.W.
      • Shanks O.E.P.
      • McClelland R.J.
      Prevalence and associated features of epilepsy in adults with Down's syndrome.


      7 (2/3/2)
      Northern IrelandAdults with DS living in community (82%) or hospitalAdults training centres, social services register, MH hospital19–50+ (community 33.5 (ns); ns, hospital 54.5 (ns); ns)nsnsnsnsnsns100
      Prasher (1995)
      • Prasher V.P.
      Epilepsy and associated effects on adaptive behaviour in adults with Down syndrome.


      4 (2/2/0)
      England, West MidlandsAdults with DS. LS hospital, community or family homeCohort with DS in West Midlands16–72 (44.2 (12.5); ns)50.718.966.713.41.0
      Pueschel et al. (1991)
      • Pueschel S.M.
      • Louis S.
      • McKnight P.
      Seizure disorders in Down syndrome.


      4 (1/3/0)
      US, Rhode IslandChildren and adults with DS. LS family home, other types nsChild development centre (enables near complete ascertainment of DS)0.5–45 (ns; ns)52.1nsnsnsnsns100
      Roizen et al. (2014)
      • Roizen N.J.
      • Magyar C.I.
      • Kuschner E.S.
      • Sulkes S.B.
      • Druschel C.
      • van Wijngaarden E.
      • et al.
      A community cross-sectional survey of medical problems in 440 children with Down syndrome in New York State.


      2 (1/1/0)
      US, New York StateChildren with DS in New York State. LS nsFamilies registered in the New York Congenital Malformations Registry (NYCMR)3–14 (7.5 (3.1); ns)51.7nsnsnsnsns100
      Tyrrell et al. (2001)
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.


      7 (2/4/1)
      IrelandAdults with DS over age 35. Dementia 13.3%. LS institutional, residential, communityLearning disability services35–70+ (ns; ns)nsnsnsnsns100
      Authors, year and quality score
      Presented as Total score (epilepsy definition score/ascertainment of epilepsy score/subgroup analysis score).
      Method epilepsy ascertainmentEpilepsy definitionEpilepsy prevalence % in main subgroup conditionsEpilepsy cases nSample size NEpilepsy prevalence %
      Airaksinen et al. (2000)
      • Airaksinen E.M.
      • Matilainen R.
      • Mononen T.
      • Mustonen K.
      • Partanen J.
      • Jokela V.
      • et al.
      A population-based study on epilepsy in mentally retarded children.


      10 (2/4/4)
      Parent questionnaire and interview, medical records, examination, EEGILAE, epilepsyCP 62.5%3215121.2
      Arvio and Sillanpää (2003)
      • Arvio M.
      • Sillanpää M.
      Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.


      4 (0/3/1)
      ns assume medical recordsEpilepsy, nsDS, 30%

      AE 83%

      FXS 5.5%
      23946151.8
      Benassi et al. (1990)
      • Benassi G.
      • Guarino M.
      • Cammarata S.
      • Cristoni P.
      • Fantini M.P.
      • Ancona A.
      • et al.
      An epidemiological study on severe mental retardation among schoolchildren in Bologna, Italy.


      3 (0/3/0)
      Medical records and discussion with school health serviceEpilepsy, nsns279030.0
      Christianson et al. (2002)
      • Christianson A.L.
      • Zwane M.E.
      • Manga P.
      • Rosen E.
      • Venter A.
      • Downs D.
      • et al.
      Children with intellectual disability in rural South Africa: prevalence and associated disability.


      3 (0/2/1)
      Phase 1 TQQ screening, phase 2 paediatric evaluationEpilepsy, nsns3723815.5
      David et al. (2014)
      • David M.
      • Dieterich K.
      • de Villemeur A.B.
      • Jouk P.S.
      • Counillon J.
      • Larroque B.
      • et al.
      Prevalence and characteristics of children with mild intellectual disability in a French county.


      4 (0/3/1)
      Carer telephone interview and medical recordsEpilepsy, nsns51812.8
      Dekker and Koot (2003)
      • Dekker M.C.
      • Koot H.M.
      DSM-IV disorders in children with borderline to moderate intellectual disability. I: prevalence and impact.


      2 (0/2/0)
      Parent interviewEpilepsy, nsns26
      Calculated from available figures not reported directly.
      4745.5
      Fernell (1998)
      • Fernell E.
      Aetiological factors and prevalence of severe mental retardation in children in a Swedish municipality: the possible role of consanguinity.


      3 (0/3/0)
      Medical records, author personal knowledgeEpilepsy, nsns176426.6
      Forsgren et al. (1990)
      • Forsgren L.
      • Edvinsson S.O.
      • Blomquist H.K.
      • Heijbel J.
      • Sidenvall R.
      Epilepsy in a population of mentally retarded children and adults.


      8 (2/2/4)
      Asked staff in institutions and letters to parents or carers, medical records examined if reported epilepsyActive ≥ 1 SZ last 5 yrs and/or on AEDFXS 23.5%

      DS 5.9%

      RS 80% (4/5)
      299147920.2
      Gittins and Rose (2008)
      • Gittins D.
      • Rose N.
      An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.


      5 (1/3/1)
      Case notesEpilepsy in case notesns396163.9
      Goulden et al. (1991)
      • Goulden K.J.
      • Shinnar S.
      • Koller H.
      • Katz M.
      • Richardson S.A.
      Epilepsy in children with mental retardation: a cohort study.


      9 (2/3/4)
      Parent interview and/or records (medical, education, social work)ILAE, epilepsyCP 37.5%, postnatal injury 73.3%, Genetic or malformation e.g. DS 12.5%3321515.3
      Hand and Reid (1996)
      • Hand J.E.
      • Reid P.M.
      Older adults with lifelong intellectual handicap in New Zealand: prevalence, disabilities and implications for regional health authorities.


      1 (0/1/0)
      Questionnaire completed by carer, staff or GPsEpilepsy, nsns177106316.7
      Haveman et al. (2011)
      • Haveman M.
      • Perry J.
      • Salvador-Carulla L.
      • Walsh P.N.
      • Kerr M.
      • Van Schrojenstein Lantman-de Valk H.
      • et al.
      Ageing and health status in adults with intellectual disabilities: results of the European POMONA II study.


      4 (1/2/1)
      Carer interviewDiagnosis epilepsyns351
      Calculated from available figures not reported directly.
      125328
      Hove and Havik (2010)
      • Hove O.
      • Havik O.E.
      Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.


      1 (0/1/0)
      Informant questionnaire (personnel)Epilepsy, nsns134
      Calculated from available figures not reported directly.
      59322.6
      Jelliffe-Pawlowski et al. (2003)
      • Jelliffe-Pawlowski L.L.
      • Shaw G.M.
      • Nelson V.
      • Harris J.A.
      Risk of mental retardation among children born with birth defects.


      5 (1/3/1)
      Service recordsDiagnosis epilepsyns16060326.5
      Calculated from available figures not reported directly.
      Koskentausta et al. (2002)
      • Koskentausta T.
      • Iivanainen M.
      • Almqvist F.
      Psychiatric disorders in children with intellectual disability.


      4 (0/3/1)
      Case recordsEpilepsy, nsPsychiatrically non-disturbed 35%, disturbed 37%5515535.5
      Lakhan (2013)
      • Lakhan R.
      Intelligence quotient is associated with epilepsy in children with intellectual disability in India.


      7 (0/4/3)
      Examination. EEG if symptoms of epilepsyEpilepsy, nsCP 46.3%, DS 10.5%6226223.7
      Lewis et al. (2000)
      • Lewis J.N.
      • Tonge B.J.
      • Mowat D.R.
      • Einfeld S.L.
      • Siddons H.M.
      • Rees V.W.
      Epilepsy and associated psychopathology in young people with intellectual disability.


      (2000)

      3 (1/2/0)
      Carer interviewSeizures or epilepsy, lifetimens.11539229.3
      Lin et al. (2003)
      • Lin J.-D.
      • Wu J.L.
      • Lee P.N.
      Healthcare needs of people with intellectual disability in institutions in Taiwan: outpatient care utilization and implications.


      1 (0/1/0)
      Parent or carer questionnaireEpilepsy, nsns262111623.5
      Calculated from available figures not reported directly.
      Matthews et al. (2008)
      • Matthews T.
      • Weston N.
      • Baxter H.
      • Felce D.
      • Kerr M.
      A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.


      3 (1/2/0)
      Carer interview. If epilepsy, visit by epilepsy nurse and information assessed by 2 doctors (and neuropsychiatrist if needed)Diagnosis epilepsyns5831818.2
      McBrien and Macken (2009)
      • McBrien J.
      • Macken S.
      Meeting the health care needs of school-age children with intellectual disability.


      3 (0/3/0)
      Medical records (moderate), routine medical review (severe or profound)Epilepsy, nsns359736.1
      McCarron et al. (2014)
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.


      6 (1/2/3)
      Questionnaire and interview (carer)Diagnosis epilepsyDS and dementia 52.2%, DS controlling for dementia 13.4%22974730.7
      McDermott et al. (2005)
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.


      6 (2/3/1)
      Medical records≥1 AEDDS 13.6%, CP 40%186
      Calculated from available figures not reported directly.
      66328.1
      McGrother et al. (2006)
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.


      6 (1/2/3)
      Carer interviewsSuffers epilepsy (ns), seizures ≥occasionally, or on AEDns620239325.9
      Memisevic and Sinanovic (2009)
      • Memisevic H.
      • Sinanovic O.
      Epilepsy in children with intellectual disability in Bosnia and Herzegovina: effects of sex, level and etiology of intellectual disability.


      7 (1/3/3)
      Medical recordsDiagnosis epilepsyDS 0%,

      other genetic cause 31.8%,

      brain injury 48.6%
      3416720.4
      Molteno et al. (2001)
      • Molteno G.
      • Molteno C.D.
      • Finchilescu G.
      • Dawes A.R.L.
      Behavioural and emotional problems in children with intellectual disability attending special schools in Cape Town, South Africa.


      1 (0/1/0)
      Teacher questionnaireEpilepsy, nsns8435523.7
      Morgan et al. (2003)
      • Morgan C.L.I.
      • Baxter H.
      • Kerr M.P.
      Prevalence of epilepsy and associated health service utilization and mortality among patients with intellectual disability.


      7 (1/3/3)
      Codes in multiple databasesEpilepsy code in inpatient, MH hospital or mortality datasets, or on epilepsy clinic databasens257159516.1
      Murphy et al. (1995)
      • Murphy C.C.
      • Yeargin-Allsopp M.
      • Decouflé P.
      • Drews C.D.
      The administrative prevalence of mental retardation in 10-year-old children in metropolitan Atlanta, 1985 through 1987.


      4 (0/3/1)
      RecordsEpilepsy, nsns157107414.6
      Calculated from available figures not reported directly.
      Nordin and Gillberg (1996)
      • Nordin V.
      • Gillberg C.
      Autism spectrum disorders in children with physical or mental disability or both. I. Clinical and epidemiological aspects.


      6 (2/4/0)
      Clinical interview and medical examination≥1 SZ or AED in last yr or SZs important part of medical historyns2210121.8
      Pawar and Akuffo (2008)
      • Pawar D.G.
      • Akuffo E.O.
      Comparative survey of comorbidities in people with learning disability with and without epilepsy.


      7 (1/3/3)
      Case recordsDiagnosis epilepsyns5317729.9
      Schieve et al. (2009)
      • Schieve L.A.
      • Boulet S.L.
      • Boyle C.
      • Rasmussen S.A.
      • Schendel D.
      Health of children 3 to 17 years of age with Down syndrome in the 1997–2005 national health interview survey.


      4 (1/2/1)
      Family carer interviewSZ past 12 mthsDS 1.4%, non-DS 16.3% (weighted estimates)9875013.1
      Calculated from available figures not reported directly.
      Schieve et al. (2012)
      • Schieve L.A.
      • Gonzalez V.
      • Boulet S.L.
      • Visser S.N.
      • Rice C.E.
      • Van Naarden Braun K.
      • et al.
      Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.


      3 (1/2/0)
      Carer interviewSZ past 12 mthsnsns

      36
      Calculated from available figures not reported directly.
      23815.1 (weighted)
      Steffenburg et al. (1995)
      • Steffenburg U.
      • Hagberg G.
      • Viggedal G.
      • Kyllerman M.
      Active epilepsy in mentally retarded children. I. Prevalence and additional neuro-impairments.


      6 (2/3/1)
      Medical filesILAE Active ≥2 unprovoked SZ and ≥1 SZ in last 5 yrsCP 72.4%
      Calculated from available figures not reported directly.
      9837825.9
      Strømme and Hagberg (2000)
      • Strømme P.
      • Hagberg G.
      Aetiology in severe and mild mental retardation: a population based study of Norwegian children.


      7 (2/4/1)
      Parent interview and examinationILAE, epilepsyns3517819.7
      Temtamy et al. (1994)
      • Temtamy S.A.
      • Kandil M.R.
      • Demerdash A.M.
      • Hassan W.A.
      • Meguid N.A.
      • Afifi H.H.
      An epidemiological/genetic study of mental subnormality in Assiut Governorate, Egypt.


      4 (0/4/0)
      Clinical examinationEpilepsy, nsns51164.3
      Tenenbaum et al. (2012)
      • Tenenbaum A.
      • Fuchs B.S.
      • Raskas M.
      • Carmeli E.
      • Aspler S.
      • Merrick J.
      National survey 2009 on medical services for persons with intellectual disability in residential care in Israel.


      1 (0/1/0)
      Residential centre report, assumed recordsEpilepsy, nsns2313706732.7
      van Schrojenstein Lantman-de Valk et al. (2000)
      • van Schrojenstein Lantman-De Valk H.M.J.
      • Metsemakers J.F.M.
      • Haveman M.J.
      • Crebolder H.F.J.M.
      Health problems in people with intellectual disability in general practice: a comparative study.


      4 (1/3/0)
      Electronic GP medical recordsEpilepsy code N88 ICPCns3531811.0
      van Schrojenstein Lantman-de Valk et al. (1997)
      • van Schrojenstein Lantman-de Valk H.M.
      • van den Akker M.
      • Maaskant M.A.
      • Haveman M.J.
      • Urlings H.F.
      • Kessels A.G.
      • et al.
      Prevalence and incidence of health problems in people with intellectual disability.


      4 (0/1/3)
      GP questionnaireEpilepsy, nsDS 10.7%, non-DS 17.4%.

      OR for epilepsy if dementia 8.8 (95% CI 4.8–16.2)
      167
      Calculated from available figures not reported directly.
      102016.4
      Wellesley et al. (1992)
      • Wellesley D.G.
      • Hockey K.A.
      • Montgomery P.D.
      • Stanley F.J.
      Prevalence of intellectual handicap in Western Australia: a community study.


      7 (2/3/2)
      Records. Clarification if needed via examination or contacting doctor (main source records)≥2 major or minor convulsions in absence of feverns208159013.1
      Wong (2011)
      • Wong C.W.
      Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.


      5 (1/1/3)
      Nursing staff questionnaireDiagnosis epilepsyDS 13.2%, non-DS 37.0%27681134.0
      Yousef (1995)
      • Yousef J.M.S.
      Epilepsy in a sample of children with intellectual disability in Jordan.


      6 (0/3/3)
      School records and teachers to clarify if necessaryEpilepsy, nsns7537919.8
      Down syndrome studies
      Collacott (1993)
      • Collacott R.A.
      Epilepsy, dementia and adaptive behaviour in Down's syndrome.


      7 (2/3/2)
      Carer interviews and medical records≥3 SZ in 2 yrs, lifetimeDementia 27.8%3535110.0
      Johannsen et al. (1996)
      • Johannsen P.
      • Christensen J.E.J.
      • Goldstein H.
      • Nielsen V.K.
      • Mai J.
      Epilepsy in Down syndrome: prevalence in three age groups.


      7 (2/4/1)
      Parent/carer interview and examinationILAE, epilepsyns127216.7
      McCarron et al. (2005)
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.


      4 (0/3/1)
      Medical recordsEpilepsy, nsAD 55.5%, non-AD 11.4%,

      end-stage AD 84.0%,

      mid-stage AD 39.4%
      4212433.9
      McVicker et al. (1994)
      • McVicker R.W.
      • Shanks O.E.P.
      • McClelland R.J.
      Prevalence and associated features of epilepsy in adults with Down's syndrome.


      7 (2/3/2)
      Medical records≥1 SZ in prior 2 yrs and/or on AEDns181919.4
      Prasher (1995)
      • Prasher V.P.
      Epilepsy and associated effects on adaptive behaviour in adults with Down syndrome.


      4 (2/2/0)
      Carer interview≥3 SZ in a 2 yr period and/or on AED (excludes partial complex SZ)Dementia in 34.4% of those with epilepsy, total n with dementia not identified3220115.9
      Pueschel et al. (1991)
      • Pueschel S.M.
      • Louis S.
      • McKnight P.
      Seizure disorders in Down syndrome.


      4 (1/3/0)
      Medical records and parent questionnaireSZ disorder, exclude single provoked or unprovoked SZns334058.1
      Roizen et al. (2014)
      • Roizen N.J.
      • Magyar C.I.
      • Kuschner E.S.
      • Sulkes S.B.
      • Druschel C.
      • van Wijngaarden E.
      • et al.
      A community cross-sectional survey of medical problems in 440 children with Down syndrome in New York State.


      2 (1/1/0)
      Parental questionnaireDiagnosis seizuresns304406.8
      Tyrrell et al. (2001)
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.


      7 (2/4/1)
      Medical notes, assessment (carer present)ILAE, epilepsyDementia 65.8%,

      non-dementia 13.5%
      5828320.5
      Calculated from available figures not reported directly.
      Abbreviations: ns, not stated; SZ, seizures; ILAE, International League Against Epilepsy; AED, anti-epileptic drug; DS, Down syndrome; ID, intellectual disabilities; LD, learning disabilities; CLDT, community learning disability team; MH, ‘mental handicap’; SPID, Severe or profound intellectual disabilities; LS, living situation; CP, cerebral palsy; BPSMR, Board for Provision of Services to the Mentally Retarded; MCA, multiple congenital anomalies; AE, acquired encephalopathy; FXS, Fragile X syndrome; CNS, central nervous system; TQQ, the ‘Ten Questions’ Questionnaire; OR, odds ratio; RS, Rett syndrome.
      a Calculated from available figures not reported directly.
      b Presented as Total score (epilepsy definition score/ascertainment of epilepsy score/subgroup analysis score).
      c ←, included in previous figure; →, included in next figure.
      d entry age includes those without ID in main study

      2.3 Quality assessment

      A gold standard to evaluate the quality of observational research does not exist [
      • Shamliyan T.
      • Kane R.L.
      • Dickinson S.
      A systematic review of tools used to assess the quality of observational studies that examine incidence or prevalence and risk factors for diseases.
      ]. A method for evaluating aspects of quality considered important in relation to obtaining valid estimates of the prevalence of epilepsy was developed. The selected quality indicators were:
      • 1.
        Definition of epilepsy:
        • Score 2: Definition given (e.g. ILAE)
        • Score 1: Partial definition given – some information (e.g. database codes used, epilepsy diagnosis) but incomplete
        • Score 0: Not stated (no criteria for epilepsy given)
      • 2.
        Ascertainment of epilepsy – this refers to the identification of those in the sample with epilepsy and not any subsequent follow up of those identified as having possible epilepsy. The following scores were allocated:
        • Score 1: Questionnaire self-completion by informant
        • Score 2: Interview with informant
        • Score 3: Extracted from records or databases
        • Score 4: Clinical examination
        If multiple methods were used, the highest level was entered as the score.
      • 3.
        Prevalence figures presented for subgroup(s). A score of 1 was allocated for each of the following subgroups for which prevalence figures were reported.
        • Age
        • Gender
        • Level of intellectual disability
        • Other – prevalence for other subgroup(s) given (e.g. those with dementia)
        A score was awarded if the information was presented in a bar chart, or in an alternative format such as relative risk. Scores could range from 0 to 4. Studies were not excluded based on quality scores and scores are presented in the first column of Table 1.

      2.4 Meta-analysis

      For each study, the sample size and number of cases of epilepsy in the sample were entered as effect size data in Comprehensive Meta-Analysis Version 2.2 software (www.Meta-Analysis.com). Prevalence estimates were pooled using random effects meta-analysis. For the main random effects pooled estimates, heterogeneity between studies was summarised using I2 and Q statistics. Subgroup analyses were conducted using between study moderator variables and within study subgroups. To compare across subgroups, the Q-test was used. Statistical significance was set at p value < .05.

      3. Results

      The process of identifying studies for inclusion is summarised in Appendix B. Electronic database searches identified a total of 1332 references, with 1099 remaining after removal of duplicates. Following the first examination of studies, 144 remained in a pool of articles relating to prevalence or mortality. After examination of full text articles from this pool and the addition of articles cited within these, 48 articles met the criteria for inclusion in relation to the prevalence of epilepsy and these are summarised in Table 1. Studies only including people with Down syndrome are presented separately at the end of Table 1.

      3.1 Geographical spread

      The majority of studies (42) were from high income countries, with just six studies from Low and Middle Income countries. The studies included a wide range of countries, with the greatest number for one country being seven studies from the United States [
      • Jelliffe-Pawlowski L.L.
      • Shaw G.M.
      • Nelson V.
      • Harris J.A.
      Risk of mental retardation among children born with birth defects.
      ,
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.
      ,
      • Murphy C.C.
      • Yeargin-Allsopp M.
      • Decouflé P.
      • Drews C.D.
      The administrative prevalence of mental retardation in 10-year-old children in metropolitan Atlanta, 1985 through 1987.
      ,
      • Schieve L.A.
      • Gonzalez V.
      • Boulet S.L.
      • Visser S.N.
      • Rice C.E.
      • Van Naarden Braun K.
      • et al.
      Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
      ,
      • Schieve L.A.
      • Boulet S.L.
      • Boyle C.
      • Rasmussen S.A.
      • Schendel D.
      Health of children 3 to 17 years of age with Down syndrome in the 1997–2005 national health interview survey.
      ,
      • Pueschel S.M.
      • Louis S.
      • McKnight P.
      Seizure disorders in Down syndrome.
      ,
      • Roizen N.J.
      • Magyar C.I.
      • Kuschner E.S.
      • Sulkes S.B.
      • Druschel C.
      • van Wijngaarden E.
      • et al.
      A community cross-sectional survey of medical problems in 440 children with Down syndrome in New York State.
      ].
      A large number were from European countries: five were from England [
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.
      ,
      • Collacott R.A.
      Epilepsy, dementia and adaptive behaviour in Down's syndrome.
      ,
      • Gittins D.
      • Rose N.
      An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.
      ,
      • Pawar D.G.
      • Akuffo E.O.
      Comparative survey of comorbidities in people with learning disability with and without epilepsy.
      ,
      • Prasher V.P.
      Epilepsy and associated effects on adaptive behaviour in adults with Down syndrome.
      ]; four from Ireland [
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.
      ,
      • McBrien J.
      • Macken S.
      Meeting the health care needs of school-age children with intellectual disability.
      ,
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.
      ,
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.
      ]; four from Sweden [
      • Fernell E.
      Aetiological factors and prevalence of severe mental retardation in children in a Swedish municipality: the possible role of consanguinity.
      ,
      • Forsgren L.
      • Edvinsson S.O.
      • Blomquist H.K.
      • Heijbel J.
      • Sidenvall R.
      Epilepsy in a population of mentally retarded children and adults.
      ,
      • Nordin V.
      • Gillberg C.
      Autism spectrum disorders in children with physical or mental disability or both. I. Clinical and epidemiological aspects.
      ,
      • Steffenburg U.
      • Hagberg G.
      • Viggedal G.
      • Kyllerman M.
      Active epilepsy in mentally retarded children. I. Prevalence and additional neuro-impairments.
      ]; three from Finland [
      • Koskentausta T.
      • Iivanainen M.
      • Almqvist F.
      Psychiatric disorders in children with intellectual disability.
      ,
      • Airaksinen E.M.
      • Matilainen R.
      • Mononen T.
      • Mustonen K.
      • Partanen J.
      • Jokela V.
      • et al.
      A population-based study on epilepsy in mentally retarded children.
      ,
      • Arvio M.
      • Sillanpää M.
      Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.
      ]; three from the Netherlands [
      • Dekker M.C.
      • Koot H.M.
      DSM-IV disorders in children with borderline to moderate intellectual disability. I: prevalence and impact.
      ,
      • van Schrojenstein Lantman-de Valk H.M.
      • van den Akker M.
      • Maaskant M.A.
      • Haveman M.J.
      • Urlings H.F.
      • Kessels A.G.
      • et al.
      Prevalence and incidence of health problems in people with intellectual disability.
      ,
      • van Schrojenstein Lantman-De Valk H.M.J.
      • Metsemakers J.F.M.
      • Haveman M.J.
      • Crebolder H.F.J.M.
      Health problems in people with intellectual disability in general practice: a comparative study.
      ]; two from Wales [
      • Morgan C.L.I.
      • Baxter H.
      • Kerr M.P.
      Prevalence of epilepsy and associated health service utilization and mortality among patients with intellectual disability.
      ,
      • Matthews T.
      • Weston N.
      • Baxter H.
      • Felce D.
      • Kerr M.
      A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
      ]; two from Norway [
      • Hove O.
      • Havik O.E.
      Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.
      ,
      • Strømme P.
      • Hagberg G.
      Aetiology in severe and mild mental retardation: a population based study of Norwegian children.
      ]; one study each from Scotland [
      • Goulden K.J.
      • Shinnar S.
      • Koller H.
      • Katz M.
      • Richardson S.A.
      Epilepsy in children with mental retardation: a cohort study.
      ], Northern Ireland [
      • McVicker R.W.
      • Shanks O.E.P.
      • McClelland R.J.
      Prevalence and associated features of epilepsy in adults with Down's syndrome.
      ], Bosnia and Herzegovina [
      • Memisevic H.
      • Sinanovic O.
      Epilepsy in children with intellectual disability in Bosnia and Herzegovina: effects of sex, level and etiology of intellectual disability.
      ], Italy [
      • Benassi G.
      • Guarino M.
      • Cammarata S.
      • Cristoni P.
      • Fantini M.P.
      • Ancona A.
      • et al.
      An epidemiological study on severe mental retardation among schoolchildren in Bologna, Italy.
      ], France [
      • David M.
      • Dieterich K.
      • de Villemeur A.B.
      • Jouk P.S.
      • Counillon J.
      • Larroque B.
      • et al.
      Prevalence and characteristics of children with mild intellectual disability in a French county.
      ], and Denmark [
      • Johannsen P.
      • Christensen J.E.J.
      • Goldstein H.
      • Nielsen V.K.
      • Mai J.
      Epilepsy in Down syndrome: prevalence in three age groups.
      ]; and one study included 14 European countries [
      • Haveman M.
      • Perry J.
      • Salvador-Carulla L.
      • Walsh P.N.
      • Kerr M.
      • Van Schrojenstein Lantman-de Valk H.
      • et al.
      Ageing and health status in adults with intellectual disabilities: results of the European POMONA II study.
      ].
      In addition, there were two studies from South Africa [
      • Christianson A.L.
      • Zwane M.E.
      • Manga P.
      • Rosen E.
      • Venter A.
      • Downs D.
      • et al.
      Children with intellectual disability in rural South Africa: prevalence and associated disability.
      ,
      • Molteno G.
      • Molteno C.D.
      • Finchilescu G.
      • Dawes A.R.L.
      Behavioural and emotional problems in children with intellectual disability attending special schools in Cape Town, South Africa.
      ] and two from Australia [
      • Lewis J.N.
      • Tonge B.J.
      • Mowat D.R.
      • Einfeld S.L.
      • Siddons H.M.
      • Rees V.W.
      Epilepsy and associated psychopathology in young people with intellectual disability.
      ,
      • Wellesley D.G.
      • Hockey K.A.
      • Montgomery P.D.
      • Stanley F.J.
      Prevalence of intellectual handicap in Western Australia: a community study.
      ]. Finally, one study each was included from the following countries: New Zealand [
      • Hand J.E.
      • Reid P.M.
      Older adults with lifelong intellectual handicap in New Zealand: prevalence, disabilities and implications for regional health authorities.
      ]; India [
      • Lakhan R.
      Intelligence quotient is associated with epilepsy in children with intellectual disability in India.
      ]; Taiwan [
      • Lin J.-D.
      • Wu J.L.
      • Lee P.N.
      Healthcare needs of people with intellectual disability in institutions in Taiwan: outpatient care utilization and implications.
      ]; Egypt [
      • Temtamy S.A.
      • Kandil M.R.
      • Demerdash A.M.
      • Hassan W.A.
      • Meguid N.A.
      • Afifi H.H.
      An epidemiological/genetic study of mental subnormality in Assiut Governorate, Egypt.
      ]; Israel [
      • Tenenbaum A.
      • Fuchs B.S.
      • Raskas M.
      • Carmeli E.
      • Aspler S.
      • Merrick J.
      National survey 2009 on medical services for persons with intellectual disability in residential care in Israel.
      ]; Hong Kong [
      • Wong C.W.
      Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
      ]; and Jordan [
      • Yousef J.M.S.
      Epilepsy in a sample of children with intellectual disability in Jordan.
      ].

      3.2 Study design

      Studies were almost entirely cross-sectional and based on retrospective review of records, questions completed either by self-report or interview, or clinical examination. There were three prospective cohort studies [
      • Airaksinen E.M.
      • Matilainen R.
      • Mononen T.
      • Mustonen K.
      • Partanen J.
      • Jokela V.
      • et al.
      A population-based study on epilepsy in mentally retarded children.
      ,
      • van Schrojenstein Lantman-de Valk H.M.
      • van den Akker M.
      • Maaskant M.A.
      • Haveman M.J.
      • Urlings H.F.
      • Kessels A.G.
      • et al.
      Prevalence and incidence of health problems in people with intellectual disability.
      ,
      • Goulden K.J.
      • Shinnar S.
      • Koller H.
      • Katz M.
      • Richardson S.A.
      Epilepsy in children with mental retardation: a cohort study.
      ] although in the latter authors only present prevalence rates for the last data collection round. In one retrospective study people could be included in more than one age-band estimate as there was an average of 12 years of follow-up for those with disabilities [
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.
      ].

      3.3 Meta-analysis

      Two studies were excluded from meta-analyses as they focused on seizures in the last 12 months rather than epilepsy per se [
      • Schieve L.A.
      • Gonzalez V.
      • Boulet S.L.
      • Visser S.N.
      • Rice C.E.
      • Van Naarden Braun K.
      • et al.
      Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
      ,
      • Schieve L.A.
      • Boulet S.L.
      • Boyle C.
      • Rasmussen S.A.
      • Schendel D.
      Health of children 3 to 17 years of age with Down syndrome in the 1997–2005 national health interview survey.
      ]. For prospective or retrospective cohort studies where people could be included in prevalence estimates at more than one time point, only the most recent data collection point was included. Analyses looked at subgroups using between study moderator variables, and also within study subgroups.

      3.3.1 General samples versus samples of people with Down syndrome

      An a priori decision was taken to compare studies based solely on samples of people with Down syndrome to general samples of people with intellectual disabilities. This was done in view of evidence suggesting that the prevalence of epilepsy is lower in people with Down syndrome than in general samples of people with intellectual disabilities (although these general sample figures are likely to include a number of people with Down syndrome). Whether or not studies included only people with Down syndrome was used as a between study moderator variable (see Table 2). The pooled estimate for 38 studies of general samples of people with intellectual disabilities was 22.2% (95% CI 19.6–25.1). There was significant heterogeneity between the studies (I2 = 96.4%, Q = 1025.2, df = 37, p < .001). The pooled estimate for studies including only people with Down syndrome was 13.6% (95% CI 9.9–18.4). There was significant heterogeneity between studies (I2 = 91.7%, Q = 84.3, df = 7, p < .001). Fig. 1 presents a forest plot of the 38 studies based on general samples and the 8 studies based on samples of people with Down syndrome only.
      Table 2Random effects meta-analysis pooled estimates of prevalence of epilepsy.
      SubgroupNumber of studiesPrevalence %
      Estimates based on meta-analysis using random effects model.
      95% CI lower95% CI upper
      Down syndromeQ 8.7, df 1, p .003
      Mixed sample3822.219.625.1
      Down syndrome only813.69.918.4
      Level of ID
      Excludes DS only studies.
      Q 43.4, df 2, p < .001
      All2922.219.625.0
      Less severe47.34.511.6
      More severe541.632.151.8
      Age
      Excludes DS only studies.
      Excludes less/more severe ID studies.
      Q 0.8, df 2, p .661
      Adult1223.519.528.0
      Child1221.717.926.1
      Mixed520.215.026.7
      High/LAMI
      Excludes DS only studies.
      Excludes less/more severe ID studies.
      Q 0.2, df 1, p .626
      High2522.419.725.4
      LAMI420.514.528.2
      Subgroup (including within study subgroups)
      Level of IDQ 56.0, df 1, p < .001
      Mild139.87.612.4
      Moderate/severe/profound1430.425.535.7
      Level of ID (where moderate, severe, profound available separately)Q 16.6, df 2, p < .001
      Moderate516.710.825.0
      Severe327.016.141.5
      Profound450.936.165.5
      Gender (any study where male/female figures given separately)Q 0.4, df 1, p .524
      Male924.819.630.8
      Female922.217.328.1
      Age groups
      Excludes DS only studies.
      Excludes less/more severe ID studies.
      Q 2.2, df 2, p .339
      0–181121.617.925.9
      19–49826.021.231.5
      50+721.517.026.9
      a Estimates based on meta-analysis using random effects model.
      b Excludes DS only studies.
      c Excludes less/more severe ID studies.
      Figure thumbnail gr1
      Fig. 1Forest plot of prevalence for mixed samples versus Down syndrome only.

      3.3.2 Level of intellectual disability

      For studies using general samples of people with intellectual disabilities, level of intellectual disability was used as a between study moderator variable (see Table 2). This classified studies as: ‘All’ (study representative of all levels of intellectual disability); ‘Less’ (study representative of those with less severe intellectual disabilities e.g. excludes those with severe/profound intellectual disability); ‘More’ (study representative of those with more severe intellectual disabilities e.g. excludes those with mild intellectual disability). The pooled estimate for studies including all levels of intellectual disability was 22.2% (95% CI 19.6–25.0), whereas the estimate for studies classed as ‘less severe’ was 7.3% (95% CI 4.5–11.6) and the estimate for ‘more severe’ 41.6% (95% CI 32.1–51.8). In view of the effect of level of intellectual disability on pooled prevalence estimates, subsequent analyses only included those 29 studies which included all levels of intellectual disability.

      3.3.3 Age group

      Broad age group was used as a between study moderator variable for the 29 studies which included all levels of intellectual disability and which were not restricted to people with Down syndrome. Age group was classed as adult, child, or mixed (adult and child). This was based on the main age group of the study sample, so for example a study would be classed as ‘adult’ if it included mainly adults and a small number of 16 year olds, and a study would be classed as ‘child’ if it included mainly children and a small number of 20 year olds. Estimates for these broad age groups did not differ significantly (see Table 2).

      3.3.4 Country economy

      Country economy (High or Low and Middle Income (LAMI)) was also used as a between study moderator variable for the 29 studies which included all levels of intellectual disability and which were not restricted to people with Down syndrome. Countries in which studies were undertaken were classed as ‘high income’ or ‘low and middle income’ based on the World Bank list of economies [
      • World Bank
      World Bank list of economies.
      ]. This classifies countries according to 2013 gross national income (GNI) per capita: low income, $1045 or less; lower middle income, $1046–4125; upper middle income, $4126–12,745; and high income, $12,746 or more. Taiwan (not included in country classification) was classed as High Income. One study included 14 European countries of which one was upper middle income and this study overall was classed as ‘high income’ [
      • Haveman M.
      • Perry J.
      • Salvador-Carulla L.
      • Walsh P.N.
      • Kerr M.
      • Van Schrojenstein Lantman-de Valk H.
      • et al.
      Ageing and health status in adults with intellectual disabilities: results of the European POMONA II study.
      ]. There was no significant difference in the pooled estimates (see Table 2).

      3.4 Within study subgroup analyses

      Further meta-analyses were then conducted which included information on prevalence from within study subgroups, for example where studies presented prevalence rates separately by level of intellectual disability, gender or age bands. Studies which only included a relevant subgroup (e.g. a sample including only people with mild intellectual disability) were also included in these analyses.

      3.4.1 Level of intellectual disability

      For level of intellectual disability, firstly prevalence rates were included for those with mild intellectual disability and the combined prevalence for those with moderate, severe or profound intellectual disability. Combining moderate, severe and profound intellectual disability was done to maximise the number of studies that could be included as few studies presented results for each of these three levels of intellectual disability separately. The pooled estimate for moderate/severe/profound intellectual disability from 14 studies was 30.4% (95% CI 25.5–35.7) compared to 9.8% (95% CI 7.6–12.4) from 13 studies for those with mild intellectual disability (see Fig. 2).
      Figure thumbnail gr2
      Fig. 2Forest plot for prevalence mild versus moderate/severe/profound intellectual disability.
      Pooled estimates were also calculated for the studies which did provide separate estimates for any of the moderate, severe or profound categories. For moderate intellectual disability, the pooled estimate was 16.7% (95% CI 10.8–25.0), compared to 27.0% (95% CI 16.1–41.5) for severe intellectual disability and 50.9% (95% CI 36.1–65.5) for profound intellectual disability.

      3.4.2 Gender

      Where male and female prevalence figures were given separately, pooled estimates were male 24.8% (95% CI 19.6–30.8) and female 22.2% (17.3–28.1). One study in the male/female subgroup analysis only included those with mild or moderate intellectual disability but was nonetheless included in the analysis [
      • Memisevic H.
      • Sinanovic O.
      Epilepsy in children with intellectual disability in Bosnia and Herzegovina: effects of sex, level and etiology of intellectual disability.
      ].

      3.4.3 Age group

      Studies presenting results separately for age bands were considered using age band as a subgroup within study. Studies presenting results for only one age band were also included in this analysis. The broad age bands used were 0–18, 19–49, and 50+. However, a 5 year leeway was given for these age bands at both the upper and lower limit so, for example, a figure for those aged 19–54 or 17–54 would be included in the 19–49 category. Age bands from McDermott et al. [
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.
      ] were not included as due to participants having an average of 12 years of follow-up time a person could be in more than one age band and they were thus not independent subgroups. Figures for a specific age (e.g. age 22) were included in the appropriate age band. Overall, there was not a significant difference by age band although the prevalence for age band 19–49 (26.0% (95% CI 21.2–31.5)) was slightly higher than that for the 0–18 age band (21.6% (95% CI 17.9–25.9) and the 50+ age group (21.5% (95% CI 17.0–26.9).

      3.5 Down syndrome

      Eight studies focussed exclusively on people with Down syndrome [
      • Collacott R.A.
      Epilepsy, dementia and adaptive behaviour in Down's syndrome.
      ,
      • Pueschel S.M.
      • Louis S.
      • McKnight P.
      Seizure disorders in Down syndrome.
      ,
      • Roizen N.J.
      • Magyar C.I.
      • Kuschner E.S.
      • Sulkes S.B.
      • Druschel C.
      • van Wijngaarden E.
      • et al.
      A community cross-sectional survey of medical problems in 440 children with Down syndrome in New York State.
      ,
      • Prasher V.P.
      Epilepsy and associated effects on adaptive behaviour in adults with Down syndrome.
      ,
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.
      ,
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.
      ,
      • McVicker R.W.
      • Shanks O.E.P.
      • McClelland R.J.
      Prevalence and associated features of epilepsy in adults with Down's syndrome.
      ,
      • Johannsen P.
      • Christensen J.E.J.
      • Goldstein H.
      • Nielsen V.K.
      • Mai J.
      Epilepsy in Down syndrome: prevalence in three age groups.
      ]. A further eight studies included some results disaggregated for people with Down syndrome in the overall sample. Results from meta-analyses in relation to people with Down syndrome are given in Table 3. In these analyses, prevalence rates from studies looking only at people with Down syndrome were combined with prevalence rates given in other studies which presented results for people with Down syndrome as a within study subgroup (excluding studies which did not include all levels of intellectual disability). No rates disaggregated by gender were identified.
      Table 3Meta-analysis estimates for people with Down syndrome.
      SubgroupNumber of studiesPrevalence %
      Estimates based on meta-analysis using random effects model.
      95% CI lower95% CI upper
      Overall prevalence including subgroups in non-DS only studies
      Excludes less/more severe ID studies.
      1312.49.116.7
      Overall prevalence including subgroups in non-DS only studies
      Excludes less/more severe ID studies.
      excluding two studies on older people
      1110.38.412.6
      Age
      Excludes less/more severe ID studies.
      Q 15.0, df 2, p .001
      0–1826.93.812.0
      19–4939.05.913.5
      50+326.016.139.2
      Has Alzheimer's/dementiaQ 30.9, df 1, p < .001
      Yes453.341.964.4
      No212.87.720.4
      a Estimates based on meta-analysis using random effects model.
      b Excludes less/more severe ID studies.
      Firstly, pooled prevalence for people with Down syndrome was estimated by combining the prevalence rates from studies looking only at people with Down syndrome with prevalence rates for people with Down syndrome presented as a within study subgroup (excluding studies which did not include all levels of intellectual disability). The pooled estimate was 12.4% (95% CI 9.1–16.7). There was significant heterogeneity between studies, I2 = 87.4%, Q = 95.3, df = 12, p < .001.
      Pooled prevalence was also estimated for age bands. This showed a significant effect of age band, with the pooled estimate rising from 6.9% (95% CI 3.8–12.0) at age 0–18, to 9.0% (95% CI 5.9–13.5) at age 19–49, and 26.0% (95% CI 16.1–39.2) at age 50+.
      In view of the increased rate of epilepsy in older people with Down syndrome, overall prevalence was then estimated excluding two studies which looked at samples of people with Down syndrome aged 35+ only [
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.
      ,
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.
      ]. Based on data from 11 studies, the pooled estimate was 10.3% (95% CI 8.4–12.6), I2 = 57.0%, Q = 23.2, df = 10, p < .01. However, it should be noted that these studies did not include all age bands, with some including only adults and other including only children.
      Finally, a small number of studies presented prevalence rates separately for those with and without Alzheimer's disease/dementia. The pooled prevalence for those with Alzheimer's/dementia was 53.3% (95% CI 41.9–64.4) compared to 12.8% (95% CI 7.7–20.4) for those specifically noted not to have Alzheimer's/dementia. It is not possible to give the mean age for those with and without Alzheimer's disease/dementia overall. However, the mean age for both groups is available in two studies: 54.7 (SD 7.5) for those with Alzheimer's disease/dementia compared to 45.6 (SD 7.3) for those without [
      • Tyrrell J.
      • Cosgrave M.
      • McCarron M.
      • McPherson J.
      • Calvert J.
      • Kelly A.
      • et al.
      Dementia in people with Down's syndrome.
      ]; and 55.4 (SD 7.0) for those with and 50.8 (SD 5.8) for those without [
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.
      ] (see Fig. 3).
      Figure thumbnail gr3
      Fig. 3Forest plot for prevalence by Alzheimer's/dementia for people with Down syndrome.

      3.6 Co-morbidity

      A number of studies presented data on co-morbidities in people with intellectual disabilities and epilepsy.

      3.6.1 Psychiatric and behavioural problems

      One study reported that epilepsy was associated with higher levels of psychopathology [
      • Molteno G.
      • Molteno C.D.
      • Finchilescu G.
      • Dawes A.R.L.
      Behavioural and emotional problems in children with intellectual disability attending special schools in Cape Town, South Africa.
      ] and one study (controlling for age, gender and level of understanding) found associations with epilepsy and some psychological and behaviour problems [
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.
      ]. However, other studies found that people with intellectual disability and epilepsy were not more likely to have co-morbid psychiatric and/or behavioural problems than those with intellectual disabilities without epilepsy. Reported findings include: being significantly less likely to have behavioural disturbances (17.6% vs 27.9%) [
      • Arvio M.
      • Sillanpää M.
      Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.
      ]; no significant difference in the prevalence of psychiatric disorders [
      • Koskentausta T.
      • Iivanainen M.
      • Almqvist F.
      Psychiatric disorders in children with intellectual disability.
      ]; no significant differences in behavioural and emotional disturbance when controlling for level of intellectual disability [
      • Lewis J.N.
      • Tonge B.J.
      • Mowat D.R.
      • Einfeld S.L.
      • Siddons H.M.
      • Rees V.W.
      Epilepsy and associated psychopathology in young people with intellectual disability.
      ]; no significant differences in psychopathology between matched epilepsy and non-epilepsy groups [
      • Matthews T.
      • Weston N.
      • Baxter H.
      • Felce D.
      • Kerr M.
      A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
      ]; no association between epilepsy and mental health concerns, with 46.7% of those with epilepsy reporting mental health problems compared with 48.1% of those without epilepsy [
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.
      ]; no association between epilepsy and the prevalence of challenging behaviour or psychiatric conditions [
      • Pawar D.G.
      • Akuffo E.O.
      Comparative survey of comorbidities in people with learning disability with and without epilepsy.
      ]; and no significant difference in maladaptive behaviour scores for those with Down syndrome and epilepsy [
      • Prasher V.P.
      Epilepsy and associated effects on adaptive behaviour in adults with Down syndrome.
      ].

      3.6.2 Physical impairments

      People with intellectual disabilities and epilepsy were found to have more associated impairments (2.7) than those without epilepsy (1.2) and were more likely to have: speech handicap (73.6% versus 50.0%), motor handicap (54.4% versus 14.4%), and blindness (14.2% versus 1.4%) [
      • Arvio M.
      • Sillanpää M.
      Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.
      ]. Other reported co-morbidities in those with epilepsy were: cerebral palsy (33.4%) and visual impairment (12.4%) [
      • Forsgren L.
      • Edvinsson S.O.
      • Blomquist H.K.
      • Heijbel J.
      • Sidenvall R.
      Epilepsy in a population of mentally retarded children and adults.
      ]; cerebral palsy (36.4%) [
      • Goulden K.J.
      • Shinnar S.
      • Koller H.
      • Katz M.
      • Richardson S.A.
      Epilepsy in children with mental retardation: a cohort study.
      ]; and cerebral palsy (43%) and visual impairment (24.5%) [
      • Steffenburg U.
      • Hagberg G.
      • Viggedal G.
      • Kyllerman M.
      Active epilepsy in mentally retarded children. I. Prevalence and additional neuro-impairments.
      ]. After adjusting for age, gender and level of understanding, those with epilepsy were more likely to have: a range of physical disabilities (adjusted OR 1.8, 95% CI 1.5–2.2); problems with wetting (OR 2.7, 95% CI 2.1–3.4), soiling (OR 2.2, 95% CI 1.6–3.1) and walking (OR 2.5, 95% CI 2.0–3.2) [
      • McGrother C.W.
      • Bhaumik S.
      • Thorp C.F.
      • Hauck A.
      • Branford D.
      • Watson J.M.
      Epilepsy in adults with intellectual disabilities: prevalence, associations and service implications.
      ]. Those with intellectual disability were also found to be more likely to have joint disease (29.3% versus 16.8% for those with intellectual disability without epilepsy, adjusted OR 2.1, 95% CI 1.5–3.1), gastrointestinal disease (34.5% versus 23.4%, adjusted OR 1.8, 95% CI 1.3–2.5), and stroke (5.2% versus 1.9%, adjusted OR 3.3, 95% CI 1.4–9.0) [
      • McCarron M.
      • O’Dwyer M.
      • Burke E.
      • McGlinchey E.
      • McCallion P.
      Epidemiology of epilepsy in older adults with an intellectual disability in Ireland: associations and service implications.
      ].

      4. Discussion

      Despite the variation in reported prevalence rates between studies, it is clear that the prevalence of epilepsy is high in people with intellectual disabilities worldwide. The results suggest that in general samples of people with intellectual disabilities, approximately one in five people will have epilepsy, with the pooled estimate from 38 studies being 22.2% (95% CI 19.6–25.1). For samples of people with Down syndrome excluding two studies focusing on older people, the rate is lower with approximately one in ten people having epilepsy, with the pooled estimate from data in 11 studies being 10.3% (95% CI 8.4–12.6). In studies where this information was available, those with intellectual disabilities and epilepsy had more physical impairments than those without epilepsy. However, whilst psychiatric or behavioural co-morbidity was common, rates were not necessarily higher than in those with intellectual disabilities without epilepsy. A review specifically addressing co-morbidity in people with intellectual disabilities and epilepsy extending beyond studies that present figures on prevalence (e.g. [
      • Arshad S.
      • Winterhalder R.
      • Underwood L.
      • Kelesidi K.
      • Chaplin E.
      • Kravariti E.
      • et al.
      Epilepsy and intellectual disability: does epilepsy increase the likelihood of co-morbid psychopathology?.
      ]) would be a useful addition to the literature.
      The prevalence of epilepsy is related to level of intellectual disability. In 29 studies which included all levels of intellectual disability, the pooled estimate was 22.2% (95% CI 19.6–25.0), whilst for four studies with samples skewed towards less severe intellectual disability the pooled estimate was 7.3% (95% CI 4.5–11.6) and for five studies skewed towards more severe intellectual disability the pooled estimate was 41.6% (95% CI 32.1–51.8). Similarly, data from 13 studies gives a pooled estimate for those with mild intellectual disability of 9.8% (95% CI 7.6–12.5) compared to 30.4% (95% CI 25.5–35.7) for those with moderate, severe or profound intellectual disability. Few studies give figures separately for those with moderate, severe or profound intellectual disability but it is clear that prevalence increases with level of intellectual disability. The pooled estimate for moderate intellectual disability from five studies was 16.7% (95% CI 10.8–25.0), for severe intellectual disability from three studies 27.0% (95% CI 16.1–41.5) and for profound intellectual disability from four studies 50.9% (95% CI 36.1–65.5).
      Age was not found to be a significant factor for general samples of people with intellectual disabilities, although the rate for those aged 19–49 was slightly higher at 26.0% (95% CI 21.2–31.5) than for 0–18 year olds (21.6%, 95% CI 17.9–25.9) and 50+ year olds (21.5%, 95% CI 17.0–26.9). However, for people with Down syndrome there was a clear increase in prevalence with age. Data from two studies for those aged 0–18 gave a pooled estimate of 6.9% (95% CI 3.8–12.0), compared to 9.0% (95% CI 5.9–13.5) for three studies giving data for 19–49 year olds and 26.0% (95% CI 16.1–39.2) for three studies giving data for those aged 50 or more. An increase with age was also found for people with Down syndrome in a study by van Schrojenstein Lantman-de Valk et al. [
      • van Schrojenstein Lantman-de Valk H.M.
      • van den Akker M.
      • Maaskant M.A.
      • Haveman M.J.
      • Urlings H.F.
      • Kessels A.G.
      • et al.
      Prevalence and incidence of health problems in people with intellectual disability.
      ], with the rates being 4.9% at age 0–19, rising to 36.4% for those age 60 or more. However, it was not possible to include these figures in the meta-analysis as sample sizes for individual age bands were not identified. Similarly, an increasing prevalence of epilepsy with age was found for a small sample of people with Down syndrome [
      • McDermott S.
      • Moran R.
      • Platt T.
      • Wood H.
      • Isaac T.
      • Dasari S.
      Prevalence of epilepsy in adults with mental retardation and related disabilities in primary care.
      ] but these figures could not be included in the meta-analysis due to participants being included in more than one age band estimate depending on the number of years the person was followed up for.
      Overall, it is clear that for people with Down syndrome, epilepsy prevalence increases with age. This increase is likely to be mainly accounted for by the increasing presence of Alzheimer's disease/dementia in people with Down syndrome as they age. The pooled estimate for those with Alzheimer's disease/dementia from four studies was 53.3% (95% CI 41.9–64.4) compared to 12.8% (95% CI 7.7–20.4) for two studies explicitly giving data for those without Alzheimer's/dementia. Further, in one study, epilepsy was found here to be significantly more common in persons at end-stage (84.0%) versus persons at mid-stage Alzheimer's disease (39.4%) [
      • McCarron M.
      • Gill M.
      • McCallion P.
      • Begley C.
      Health co-morbidities in ageing persons with Down syndrome and Alzheimer's dementia.
      ].

      4.1 Limitations

      There are a number of limitations to this review. Whilst studies were identified from a large range of countries, the review is restricted to English language publications. All data was extracted by one reviewer and extraction of data by two reviewers independently would have reduced the possibility of errors. In some instances it was necessary to calculate figures from reported data as they were not reported explicitly (e.g. obtaining the number of epilepsy cases from the overall sample number and reported prevalence rate or vice versa) and two minor discrepancies arose. Firstly, calculating figures from McVicker et al. [
      • McVicker R.W.
      • Shanks O.E.P.
      • McClelland R.J.
      Prevalence and associated features of epilepsy in adults with Down's syndrome.
      ] on prevalence by age band resulted in a total number of epilepsy cases of 19 compared to a reported number of 18. Secondly, calculating figures from Wong [
      • Wong C.W.
      Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
      ] on prevalence in a subgroup with Down syndrome resulted in a prevalence rate of 13.1% compared to a rate of 13.2% as reported in the article.
      Ideally, the same definition of epilepsy should be used across studies to allow comparison of prevalence rates [
      • Forsgren L.
      • Beghi E.
      • Öun A.
      • Sillanpää M.
      The epidemiology of epilepsy in Europe – a systematic review.
      ]. However, many of the studies identified did not present a definition of epilepsy, generally referring to either a diagnosis of epilepsy or the presence of epilepsy. The lack of detail given regarding the definition of epilepsy in many studies means that it is not possible to determine whether reported prevalence rates related to active epilepsy or lifetime epilepsy. The issue of defining epilepsy is not straightforward [
      • Fisher R.S.
      • Acevedo C.
      • Arzimanoglou A.
      • Bogacz A.
      • Cross J.H.
      • Elger C.E.
      • et al.
      ILAE official report: a practical clinical definition of epilepsy.
      ]. Where definitions were provided, these included standard definitions based on International League Against Epilepsy (ILAE) criteria and other definitions specifying variable criteria in relation to number of seizures, anti-epileptic drug (AED) use and time spans. In addition, the source of information used to ascertain epilepsy is variable between studies which may lead to varying levels of accuracy in obtained rates.
      In addition to the variation in prevalence rates that is likely to be due to differences in the definition of epilepsy used and the source of data in studies, there is also likely to be an unknown number of cases where epilepsy has been misdiagnosed due to the misinterpretation of behavioural, physiological, syndrome related, medication related or psychological events by parents, paid carers and health professionals [
      • Chapman M.
      • Iddon P.
      • Atkinson K.
      • Brodie C.
      • Mitchell D.
      • Parvin G.
      • et al.
      The misdiagnosis of epilepsy in people with intellectual disabilities: a systematic review.
      ].
      Finally, the review has focussed on prevalence in the general population of people with intellectual disabilities or Down syndrome and has not included studies on less common syndromes such as Fragile X syndrome. Future review work could consider prevalence in a greater range of specific syndromes associated with intellectual disabilities.

      5. Conclusion

      This review aims to provide an up to date summary of research on the prevalence of epilepsy in people with intellectual disabilities. The pooling of estimates from studies, and the examination of factors which account for some of the heterogeneity of reported prevalence rates between studies, allows for the provision of more robust figures on prevalence. With around one in five people with intellectual disabilities having epilepsy, it is important that services are equipped with the information and skills needed to manage epilepsy in this population. A recent report provides information on reasonable adjustments that can be made to improve epilepsy care for people with intellectual disabilities [
      • Marriott A.
      • Turner S.
      • Hatton C.
      • Glover G.
      • Robertson J.
      Making reasonable adjustments to epilepsy services for people with learning disabilities.
      ] The ideas, information and examples of good practice in relation to reasonable adjustments provided within this report should help services improve provision for this highly prevalent condition.

      Conflict of interest statement

      There is no conflict of interest.

      Acknowledgements

      This work was supported by Public Health England. However, the findings and views reported in this paper are those of the authors and should not be attributed to Public Health England. We would like to thank Howard Ring for comments on the draft of this manuscript.

      Appendix A. Electronic search strategy

      Tabled 1
      MEDLINE AND CINAHL
      Limits: 1990; English; Human
      (TI (learning N1 (disab* or difficult* or handicap*)) OR TI (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR TI (intellectual* N1 (disab* or impair* or handicap*)) OR TI development* N1 disab* OR TI (multipl* N1 (handicap* or disab*)) OR TI “Down* syndrome” OR (MH “Developmental Disabilities/EP/MO”) OR (MH “Intellectual Disability+/EP/MO”) OR (MH “mentally disabled persons”)) OR (AB (learning N1 (disab* or difficult* or handicap*)) OR AB (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR AB (intellectual* N1 (disab* or impair* or handicap*)) OR AB development* N1 disab* OR AB (multipl* N1 (handicap* or disab*)) OR AB“Down* syndrome”)
      AND
      (MH “Epilepsy+/MO/EP”) OR (TI epilep* OR TI seizure* OR TI convulsi* OR AB epilep* OR AB seizure* OR AB convulsi*)
      AND
      (TI incidence OR TI prevalence OR TI mortality OR TI death OR AB incidence OR AB prevalence OR AB mortality OR AB death) OR (MH “Incidence”) OR (MH “Prevalence”) OR (MH “Mortality+”)
      PSYCINFO
      Limits: 1990, Peer review, English, Exclude dissertations
      DE “Epilepsy” OR DE “Epileptic Seizures” OR (DE “Seizures” OR DE “Audiogenic Seizures” OR DE “Epileptic Seizures” OR DE “Grand Mal Seizures” OR DE “Petit Mal Seizures” OR DE “Status Epilepticus”) OR (TI epilep* OR TI seizure* OR TI convulsi* OR AB epilep* OR AB seizure* OR AB convulsi*)
      AND
      (TI incidence OR TI prevalence OR TI mortality OR TI death OR AB incidence OR AB prevalence OR AB mortality OR AB death) OR DE “Epidemiology” OR DE “death and dying” OR DE “mortality rate”
      AND
      DE “Intellectual Development Disorder” OR DE “mental retardation” OR DE “developmental disabilities” OR (TI (learning N1 (disab* or difficult* or handicap*)) OR TI (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR TI (intellectual* N1 (disab* or impair* or handicap*)) OR TI development* N1 disab* OR TI (multipl* N1 (handicap* or disab*)) OR TI “Down* syndrome”) OR AB (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR AB (intellectual* N1 (disab* or impair* or handicap*)) OR AB development* N1 disab* OR AB (multipl* N1 (handicap* or disab*)) OR AB “Down* syndrome”

      Appendix B. Flowchart of study identification

      Figure thumbnail fx1

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