Highlights
- •We summarized 977 epilepsy-associated genes, which were divided into 4 categories according to the manifestation of epilepsy in phenotypes.
- •84 epilepsy genes, i.e., genes that only cause epilepsies or syndromes with epilepsy as the core symptom.
- •73 neurodevelopment-associated genes, i.e., genes associated with gross brain developmental malformations and epilepsies.
- •536 epilepsy-related genes, i.e., genes associated with gross physical, or other systemic abnormalities and accompanied by epilepsy or seizures.
- •284 potential epilepsy-associated genes, i.e., genes that require further verification.
Abstract
Development in genetic technology has led to the identification of an increasing number of genes associated with epilepsy. These discoveries will both provide the basis for including genetic tests in clinical practice and improve diagnosis and treatment of epilepsy. By searching through several databases (OMIM, HGMD, and EpilepsyGene) and recent publications on PubMed, we found 977 genes that are associated with epilepsy. We classified these genes into 4 categories according to the manifestation of epilepsy in phenotypes. We found 84 genes that are considered as epilepsy genes: genes that cause epilepsies or syndromes with epilepsy as the core symptom. 73 genes were listed as neurodevelopment-associated genes: genes associated with both brain-development malformations and epilepsy. Several genes (536) were epilepsy-related: genes associated with both physical or other systemic abnormalities and epilepsy or seizures. We found 284 additional genes putatively associated with epilepsy; this requires further verification. These integrated data will provide new insights useful for both including genetic tests in the clinical practice and evaluating the results of genetic tests. We also summarized the epilepsy-associated genes according to their function, with the goal to better characterize the association between genes and epilepsies and to further understand the mechanisms underlying epilepsy.
Keywords
1. Introduction
Advances in genomics techniques, especially the development of next-generation sequencing, have greatly increased our knowledge on the genetic changes occurring across the entire human genome, allowing for rapid and efficient discovery of genes involved in many diseases. Epilepsies may result from primary genetic abnormalities or secondary to well-defined structural or metabolic disorders, of which, some also have genetic causes. It is estimated that more than half of epilepsies have a genetic basis [
[1]
]. The application of genomic technologies has a tremendous impact on the discovery of the genetic basis of epilepsy, and it is expected to play a pivotal role in the diagnosis and treatment of epilepsy. However, epilepsies associated with genetic abnormalities display large heterogeneity. Mutations in some genes may selectively cause epilepsies or syndromes with epilepsy as the core symptom (e.g., SCN1A mutations cause epilepsies with febrile seizures plus [[2]
]), while other genes may be associated with gross brain developmental malformations and epilepsies (e.g., mutations in TSC1 and TSC2 genes cause tuberous sclerosis [3
, 4
]). Seizures may also occur in other genetic disorders affecting the central nervous system, such as Fragile X Syndrome [[5]
] and myoclonus-dystonia [[6]
]. Therefore, it is a challenge to decide which gene, or group of genes, should be characterized in a specific target patient population before designing an efficient and cost-effective genetic-testing strategy. In this review, we present a summary of the genes associated with epilepsy. We grouped the genes according to the manifestation of epilepsy in the phenotype, i.e., whether epilepsy is the exclusive outcome of the mutation or part of a group of unrelated symptoms. The aim of the present review is to offer an insight into the genes that should be included in the genetic testing of patients with a distinct phenotype. The association between genes and epilepsy will further our knowledge on the role played by specific mutations in epilepsy and the mechanisms underlying epileptogenesis.2. Methods
To obtain a comprehensive list of genes associated with epilepsy, a thorough search of online databases was conducted. Briefly, we searched the Online Mendelian Inheritance in Man database (OMIM, http://www.ncbi.nlm.nih.gov/omim/) with the following query terms: “epilepsy/epilepsies/epileptic” or “seizure/seizures.” We then crosschecked the findings with the results from the searches performed on the Human Gene Mutation Database (HGMD, http://www.hgmd.cf.ac.uk/ac/index.php) and the EpilepsyGene database (http://61.152.91.49/EpilepsyGene/). Additionally, recent publications relevant to epilepsy were searched on PubMed (http://www.ncbi.nlm.nih.gov/pubmed/).
More than 2000 items were retrieved from the OMIM database. These items were further analyzed through thorough reading and double-checked manually by two experts in the field of epilepsy. The items related to epilepsy and well-characterized gene mutations were included. We used the following criteria to exclude articles from the analysis: (1) clinical genetic reports without definite molecular genetic confirmation, (2) linkage analysis without identification of specific genes, (3) genomic rearrangement without the causative gene defined, (4) clinical syndrome potentially related to epilepsy; however, the patients with epilepsy were not subjected to a genetic test. Finally, 693 genes were identified to be associated with epilepsy. The phenotypes of these genes exhibit a large variability in epilepsy and other clinical manifestations. According to the manifestation of epilepsy in phenotypes, these genes were divided into 3 categories: (1) epilepsy genes, i.e., genes that only cause epilepsies or syndromes with epilepsy as the core symptom; (2) neurodevelopment-associated epilepsy genes, i.e., genes associated with gross brain developmental malformations and epilepsies; and (3) epilepsy-related genes, i.e., genes associated with gross physical, or other systemic abnormalities and accompanied by epilepsy or seizures.
After crosschecking the HGMD and EpilepsyGene databases, we found 247 additional genes, not present in the OMIM database, potentially associated with epilepsy. We did not include the 248 genes that were presented in the EpilepsyGene database but were not described to be associated with epilepsy in the original report [
[7]
]. Furthermore, considering that some of the genes which have been recently reported to be involved in epilepsy may not be present in any of the three databases, we searched PubMed for recent publications (i.e., since 2014) relevant to epilepsy. This last search yielded 37 more genes potentially associated with epilepsy.3. Results
3.1 Epilepsy genes
Based on the results from the search in the OMIM database, 84 genes were classified as epilepsy genes. Mutations in these genes cause pure or relatively pure epilepsies, or syndromes with epilepsy as the core symptom. This category also includes genes that may be associated with multiple phenotypes other than epilepsy or seizures; however, an individual with mutations in these genes may present only epilepsy or seizures. For example, PRRT2 mutations are associated with several clinical syndromes such as paroxysmal dyskinesia, infantile convulsions with paroxysmal choreoathetosis, and benign familial infantile seizures [
[8]
]. Although paroxysmal dyskinesia is the main symptom in the majority of patients, there are cases of only benign familial infantile seizures in individuals harboring this mutation. To facilitate the search for causative genes, we present a summary of these genes according to their phenotypes and sorted according to their onset age (Table 1).Table 1Epilepsy genes.
| Phenotype (in order of the onset age) | Inheritance | Gene |
|---|---|---|
| Neonatal | ||
| Pyridoxamine 5'-phosphate oxidase deficiency (PNPOD) | AR | PNPO |
| Pyridoxine-dependent epilepsy (EPD) | AR | ALDH7A1 |
| Benign familial neonatal seizures (BFNS) | AD | KCNQ2, KCNQ3 |
| Infantile and childhood | ||
| Familial infantile myoclonic epilepsy (FIME) | AR | TBC1D24 |
| Benign familial infantile seizures (BFIS) | AD | PRRT2, SCN2A, SCN8A |
| Amish infantile epilepsy syndrome (AIES) | AR | ST3GAL5 |
| Early infantile epileptic encephalopathy (EIEE) | AD | CACNA1A, GABRA1, GABRB3, KCNQ2, KCNT1, SCN2A, SCN8A |
| AR | AARS, ARV1, DOCK7, FRRS1L, GUF1, ITPA, NECAP1, PLCB1, SLC12A5, SLC13A5, SLC25A12, SLC25A22, ST3GAL3, SZT2, TBC1D24, WWOX | |
| XLD | CDKL5 | |
| XLR | ARHGEF9 | |
| XL | ALG13, PCDH19 | |
| UN | DNM1, EEF1A2, FGF12, GABRB1, GNAO1, GRIN2B, GRIN2D, HCN1, KCNA2, KCNB1, SIK1, SLC1A2, SPTAN1, STXBP1, UBA5 | |
| Dravet syndrome (DS) | AD | SCN1A, SCN9A |
| Familial febrile seizures (FFS) | AD | GABRG2, GPR98, SCN1A, SCN9A |
| AR | CPA6 | |
| Generalized epilepsy with febrile seizures plus (GEFS + ) | AD | GABRD, GABRG2, SCN1A, SCN1B, SCN9A, STX1B |
| Generalized epilepsy and paroxysmal dyskinesia (GEPD) | AD | KCNMA1 |
| Myoclonic-atonic epilepsy (MAE) | AD | SLC6A1 |
| Childhood-onset epileptic encephalopathy (COEE) | AD | CHD2 |
| Focal epilepsy and speech disorder (FESD) with or without mental retardation | AD | GRIN2A |
| Childhood absence epilepsy (CAE) | AD | GABRG2 |
| UN | CACNA1H, GABRA1, GABRB3 | |
| Juvenile and later | ||
| Juvenile absence epilepsy (JAE) | AD | CLCN2, EFHC1 |
| Juvenile myoclonic epilepsy (JME) | AD | CACNB4, CLCN2, EFHC1, GABRD |
| UN | GABRA1 | |
| Idiopathic generalized epilepsy (IGE) | AD | CACNB4, CLCN2, GABRD, SLC12A5, SLC2A1 |
| UN | CACNA1H, CASR | |
| Familial adult myoclonic epilepsy (FAME) | AD | ADRA2B |
| AR | CNTN2 | |
| Familial temporal lobe epilepsy (FTLE) | AD | CPA6, GAL, LGI1 |
| Not specific | ||
| Progressive myoclonic epilepsy (PME) | AD | KCNC1 |
| AR | CERS1, CSTB, EPM2A, GOSR2, KCTD7, LMNB2, NHLRC1, PRDM8, PRICKLE1, SCARB2 | |
| Nocturnal frontal lobe epilepsy (NFLE) | AD | CHRNA2, CHRNA4, KCNT1 |
| UN | CHRNB2 | |
| Familial focal epilepsy with variable foci (FFEVF) | AD | DEPDC5 |
Bold italics, with multiple epilepsy phenotypes.
AD, autosomal dominant; AR, autosomal recessive; UN, unknown; XL, X-linked; XLD, X-linked dominant; XLR, X-linked recessive.
AARS, alanyl-tRNA synthetase; ADRA2B, alpha-2B-adrenergic receptor; ALDH7A1, aldehyde dehydrogenase 7 family, member A1; ALG13, asparagine-linked glycosylation 13, S. cerevisiae, homolog of; ARHGEF9, RHO guanine nucleotide exchange factor 9; ARV1, ARV1, S. cerevisiae, homolog of; CACNA1A, calcium channel, voltage-dependent, P/Q type, alpha-1A subunit; CACNA1H, calcium channel, voltage-dependent, T type, alpha-1H subunit; CACNB4, calcium channel, voltage-dependent, beta-4 subunit; CASR, calcium-sensing receptor; CDKL5, cyclin-dependent kinase-like 5; CERS1, ceramide synthase 1; CHD2, chromodomain helicase DNA-binding protein 2; CHRNA2, cholinergic receptor, neuronal nicotinic, alpha polypeptide 2; CHRNA4, cholinergic receptor, neuronal nicotinic, alpha polypeptide 4; CHRNB2, cholinergic receptor, neuronal nicotinic, beta polypeptide 2; CLCN2, chloride channel 2; CNTN2, contactin 2; CPA6, carboxypeptidase A6; CSTB, cystatin B; DEPDC5, DEP domain-containing protein 5; DNM1, dynamin 1; DOCK7, dedicator of cytokinesis 7; EEF1A2, eukaryotic translation elongation factor 1, alpha-2; EFHC1, EF-hand domain (C-terminal)-containing protein 1; EPM2A, EPM2A gene, encodes laforin; FGF12, fibroblast growth factor 12; FRRS1L, ferric chelate reductase 1-like; GABRA1, gamma-aminobutyric acid receptor, alpha-1; GABRB1, gamma-aminobutyric acid receptor, beta-1; GABRB3, gamma-aminobutyric acid receptor, beta-3; GABRD, gamma-aminobutyric acid receptor, delta; GABRG2, gamma-aminobutyric acid receptor, gamma-2; GAL, galanin; GNAO1, guanine nucleotide-binding protein, alpha-activating activity polypeptide O; GOSR2, golgi snap receptor complex member 2; GPR98, G protein-coupled receptor 98; GRIN2A, glutamate receptor, ionotropic, N-methyl-D-aspartate, subunit 2A; GRIN2B, glutamate receptor, ionotropic, N-methyl-D-aspartate, subunit 2B; GRIN2D, glutamate receptor, ionotropic, N-methyl-D-aspartate, subunit 2D; GUF1, GUF1 GTPase, S. cerevisiae, homolog of; HCN1, hyperpolarization-activated cyclic nucleotide-gated potassium channel 1; ITPA, inosine triphosphatase; KCNA2, potassium channel, voltage-gated, shaker-related subfamily, member 2; KCNB1, potassium channel, voltage-gated, shab-related subfamily, member 1; KCNC1, potassium channel, voltage-gated, shaw-related subfamily, member 1; KCNMA1, potassium channel, calcium-activated, large conductance, subfamily M, alpha member 1; KCNQ2, potassium channel, voltage-gated, KQT-like subfamily, member 2; KCNQ3, potassium channel, voltage-gated, KQT-like subfamily, member 3; KCNT1, potassium channel, subfamily T, member 1; KCTD7, potassium channel tetramerization domain-containing protein 7; LGI1, leucine-rich gene, glioma-inactivated, 1; LMNB2, lamin B2; NECAP1, NECAP endocytosis-associated protein 1; NHLRC1, NHL repeat-containing 1 gene; PCDH19, protocadherin 19; PLCB1, phospholipase C, beta-1; PNPO, pyridoxamine 5-prime-phosphate oxidase; PRDM8, PR domain-containing protein 8; PRICKLE1, prickle, drosophila, homolog of, 1; PRRT2, proline-rich transmembrane protein 2; SCARB2, scavenger receptor class B, member 2; SCN1A, sodium channel, neuronal type I, alpha subunit; SCN1B, sodium channel, voltage-gated, type I, beta subunit; SCN2A, sodium channel, voltage-gated, type II, alpha subunit; SCN8A, sodium channel, voltage-gated, type VIII, alpha subunit; SCN9A, sodium channel, voltage-gated, type IX, alpha subunit; SIK1, salt-inducible kinase 1; SLC1A2, solute carrier family 1 (glial high affinity glutamate transporter), member 2; SLC12A5, solute carrier family 12 (potassium/chloride transporter), member 5; SLC13A5, solute carrier family 13 (sodium-dependent citrate transporter), member 5; SLC25A12, solute carrier family 25 (mitochondrial carrier, aralar), member 12; SLC25A22, solute carrier family 25 (mitochondrial carrier, glutamate), member 22; SLC2A1, solute carrier family 2 (facilitated glucose transporter), member 1; SLC6A1, solute carrier family 6 (neurotransmitter transporter, gaba), member 1; SPTAN1, spectrin, alpha, nonerythrocytic 1; ST3GAL3, ST3 beta-galactoside alpha-2,3-sialyltransferase 3; ST3GAL5, ST3 beta-galactoside alpha-2,3-sialyltransferase 5; STX1B, syntaxin 1B; STXBP1, syntaxin-binding protein 1; SZT2, seizure threshold 2, mouse, homolog of; TBC1D24, Tre2-Bub2-Cdc16/TBC1 domain family, member 24; UBA5, ubiquitin-like modifier activating enzyme 5; WWOX, WW domain-containing oxidoreductase.
a Description on phenotype was modified after retraction of the initial report.
b Potential modifier gene.
The spectrum of epilepsy caused by gene mutations covers 23 epileptic phenotypes, ranging from the mild form of benign familial infantile seizures to the extremely severe form of early infantile epileptic encephalopathy (EIEE). More than one causative gene has been identified in 14 epileptic phenotypes. EIEE was shown to be associated with mutations in 42 genes. Progressive myoclonic epilepsy was associated with 11 pathogenic genes. Other common phenotypes with multiple genetic causes are mostly represented by idiopathic epilepsies including childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, and idiopathic generalized epilepsy. In contrast, only a single causative gene has been identified in 9 epileptic phenotypes. However, except for few cases with definite one-to-one epilepsy to gene correlation such as myoclonic-atonic epilepsy and SLC6A1, more than one genetic cause is generally expected to be identified in most of the phenotypes. For instance, CHRNA4 was initially identified as the only pathogenic gene of nocturnal frontal lobe epilepsy [
[9]
]; however, later studies demonstrated that CHRNB2, CHRNA2, and KCNT1 were also associated with this type of epilepsy [10
, 11
, 12
].The causative genes produce large variation in the inheritance pattern of the genetic epilepsies. The inheritance pattern has commonly been classified into dominant (autosomal or X-linked) or recessive (autosomal or X-linked) inheritance. However, recent studies have identified epilepsy genes with undefined inheritance, including genes with de novo mutations. De novo mutations may be associated with autosome dominant genetic disorders, such as the spectrum of epilepsies with febrile seizures plus caused by SCN1A mutations, typically in Dravet syndrome [
[2]
]. De novo mutations have been frequently identified in epileptic encephalopathies [13
, 14
, 15
, 16
]. However, as many of these children with neurodisability did not reproduce, it was unclear as to whether these are de novo dominant mutations. An exception is that EIEE caused by PCDH19 mutations included de novo mutations, but presented an inheritance of neither X-linked dominant nor recessive. EIEE displayed heterogeneity in both the genetic cause and the inheritance pattern. It is noteworthy that epileptic encephalopathies encompass several clinical subtypes such as the Lennox–Gastaut syndrome, the West syndrome, and the Landau–Kleffner syndrome. We failed to identify genetic information for each of the syndromes separately owing to the lack of detailed information available in OMIM or publications.To better understand the molecular characteristics of the products of epilepsy genes, we grouped the genes according to the protein function (Table 2). The most common epilepsy genes were ion-channel genes, which account for 28 of the 84 epilepsy genes, indicating that ion-channel genes may play an important role in epilepsy. Mutations in ion-channel genes produce a variety of epilepsies with phenotypes ranging from mild to severe. Mutations in enzyme/enzyme-modulator genes ranked as the second cause (25/84); these mainly caused the severe form of epilepsy, except mutations in CPA6 gene which cause relatively mild familial temporal-lobe epilepsy and familial febrile seizures [
[17]
]. The remaining genes included in the analysis are involved in transport, receptor binding, cell adhesion, signal transduction/molecule, membrane trafficking, cytoskeleton, nucleic acid binding, and other unknown functions.Table 2Functional categories of the epilepsy genes.
| Encoded protein function | Gene and phenotype (OMIM phenotype) |
|---|---|
| Ion channel | |
| Sodium channel | SCN1A (DS/GEFS+/FFS), SCN1 B (GEFS + ), SCN2A (EIEE/BFIS), SCN8A (EIEE/BFIS), SCN9A (GEFS+/DS/FFS) |
| Potassium channel | KCNA2 (EIEE), KCNB1 (EIEE), KCNC1 (PME), KCNMA1 (GEPD), KCNQ2 (EIEE/BFNS), KCNQ3 (BFNS), KCNT1 (NFLE/EIEE) |
| HCN channel | HCN1 (EIEE) |
| Calcium channel | CACNA1A (EIEE), CACNA1H (CAE/IGE), CACNB4 (IGE/JME) |
| Chloride channel | CLCN2 (IGE/JAE/JME) |
| GABA-A receptor | GABRA1 (EIEE/CAE/JME), GABRB1 (EIEE), GABRB3 (CAE/EIEE), GABRD (GEFS+/IGE/JME), GABRG2 (GEFS+/FFS/CAE) |
| NMDA receptor | GRIN2A (FESD), GRIN2 B (EIEE), GRIN2D (EIEE) |
| Acetylcholine receptor | CHRNA2 (NFLE), CHRNA4 (NFLE), CHRNB2 (NFLE) |
| Enzyme/Enzyme modulator | |
| Enzyme | AARS (EIEE), ALDH7A1 (EPD), ALG13 (EIEE), CDKL5 (EIEE), CERS1 (PME), CHD2 (COEE), CPA6 (FTLE/FFS), DNM1 (EIEE), EPM2A (PME), GNAO1 (EIEE), GUF1 (EIEE), ITPA (EIEE), NHLRC1 (PME), PLCB1 (EIEE), PNPO (PNPOD), PRDM8 (PME), SIK1 (EIEE), ST3GAL3 (EIEE), ST3GAL5 (AIES), UBA5 (EIEE), WWOX (EIEE) |
| Enzyme modulator | ARHGEF9 (EIEE), CSTB (PME), DOCK7 (EIEE), TBC1D24 (EIEE/FIME) |
| Transporter/Receptor | |
| Transporter | SLC1A2 (EIEE), SLC12A5 (EIEE/IGE), SLC13A5 (EIEE), SLC25A12 (EIEE), SLC25A22 (EIEE), SLC2A1 (IGE), SLC6A1 (MAE) |
| Receptor | ADRA2 B (FAME), CASR (IGE), FRRS1L (EIEE), GPR98 (FFS), SCARB2 (PME) |
| Cell adhesion molecule | CNTN2 (FAME), PCDH19 (EIEE) |
| Signal transduction/molecule | EFHC1 (JAE/JME), FGF12 (EIEE) |
| Membrane trafficking | GOSR2 (PME), STX1 B (GEFS+), STXBP1 (EIEE) |
| Cytoskeletal protein | LMNB2 (PME), SPTAN1 (EIEE) |
| Nucleic acid binding | EEF1A2 (EIEE), GUF1 (EIEE) |
| Unclassified | ARV1 (EIEE), DEPDC5 (FFEVF), GAL (FTLE), KCTD7 (PME), LGI1 (FTLE), NECAP1 (EIEE), PRICKLE1 (PME), PRRT2 (BFIS), SZT2 (EIEE) |
Bold italics, with multiple functional classifications.
AIES, Amish infantile epilepsy syndrome; BFIS, benign familial infantile seizures; BFNS, benign familial neonatal seizures; CAE, childhood absence epilepsy; COEE, childhood-onset epileptic encephalopathy; DS, Dravet syndrome; EIEE, early infantile epileptic encephalo-pathy; EPD, pyridoxine-dependent epilepsy; FAME, familial adult myoclonic epilepsy; FESD, focal epilepsy and speech disorder with or without mental retardation; FFEVF, familial focal epilepsy with variable foci; FFS, familial febrile seizures; FIME, familial infantile myoclonic epilepsy; FTLE, familial temporal lobe epilepsy; GEFS+, generalized epilepsy with febrile seizures plus; GEPD, generalized epilepsy and paroxysmal dyskinesia; IGE, idiopathic generalized epilepsy; JAE, juvenile absence epilepsy; JME, juvenile myoclonic epilepsy; MAE, myoclonic-atonic epilepsy; NFLE, nocturnal frontal lobe epilepsy; PME, progressive myoclonic epilepsy; PNPOD, pyridoxamine 5'-phosphate oxidase deficiency.
a Description on phenotype was modified after retraction of the initial report.
Table 2 shows that 17 epilepsy genes are involved in more than one epileptic phenotype. Theoretically, the impairment caused by mutations in a gene may vary in severity, thereby correlating with the severity of the phenotype. This is typically observed in epilepsies caused by SCN1A mutations which produce a spectrum of phenotypes ranging from the mild form of generalized epilepsies with febrile seizures plus, or pure febrile seizures [
18
, 19
], to the extremely severe form of the Dravet syndrome [20
, 21
], and there was a correlation between the genotypes or function alterations (functional-type or funotype) and phenotypes [[2]
]. Similar correlations have been observed in epilepsies caused by mutations in KCNQ2 and GABRA1. For some genes, such as SCN2A and SCN8A, although mild and severe cases have been reported following their mutations, a correlation between genotype (or funotype) and phenotype has not been found yet. Thus, the pathogenic role played by these genes in epilepsy requires further investigation.3.2 Neurodevelopment-associated epilepsy genes
In total, 73 genes were classified as neurodevelopment-associated epilepsy genes. Mutations in these genes produce gross neurodevelopmental malformations and epilepsy, which may vary in severity. Mutations in some genes, such as TSC1 and TSC2, cause the tuberous sclerosis, which may be accompanied by severe epilepsy [
3
, 4
]. Other genes, such as TUBB3 and WDR62, are associated with characteristic brain developmental malformations but infrequent epileptic seizures [22
, 23
].With the development of neuroimaging techniques, identification of the neurodevelopmental malformation provides critical evidences for the diagnosis and classification of the phenotype. We reviewed these genes according to the localization of brain malformations, which vary from focal (or multifocal) to general brain malformation. These brain malformations may be accompanied by physical or other systemic abnormalities (Table 3). It should be noted that gene mutations have also been identified in cases with subtle or undetectable malformations.
Table 3Neurodevelopment-associated epilepsy genes.
| Phenotype | Inheritance | Gene |
|---|---|---|
| Focal or multifocal brain malformation | ||
| Grey matter | ||
| Holoprosencephaly | AD | PTCH1 |
| Band-like calcification with simplified gyration and polymicrogyria | AR | OCLN |
| Bilateral frontoparietal polymicrogyria | AR | GPR56 |
| Bilateral perisylvian polymicrogyria | UN | GPR56 |
| Bilateral temporooccipital polymicrogyria | AR | FIG4 |
| CK syndrome | XLR | NSDHL |
| Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome | AD | PIK3R2 |
| Polymicrogyria with optic nerve hypoplasia | AR | TUBA8 |
| Rolandic epilepsy, speech dyspraxia, and mental retardation | UN | SRPX2 |
| Symmetric or asymmetric polymicrogyria | AD | TUBB2B |
| Periventricular heterotopia | XLD | FLNA |
| Periventricular heterotopia with microcephaly | AR | ARFGEF2 |
| Periventricular nodular heterotopia | AD | ERMARD |
| Subcortical laminar heterotopia | XL | DCX |
| UN | PAFAH1B1 | |
| Tuberous sclerosis | AD | TSC1, TSC2 |
| Complex cortical dysplasia with other brain malformations | AD | KIF2A, KIF5C, TUBB2A, TUBB3, TUBG1 |
| Cortical dysplasia-focal epilepsy syndrome | UN | CNTNAP2 |
| Occipital cortical malformations | AR | LAMC3 |
| Pontocerebellar hypoplasia | AR | AMPD2, CLP1, EXOSC3, PCLO, SEPSECS, TSEN2, TSEN54, VPS53 |
| UN | TSEN15 | |
| Mental retardation, X-linked, with cerebellar hypoplasia and distinctive facial appearance | XLR | OPHN1 |
| Dentatorubro-pallidoluysian atrophy | AD | ATN1 |
| Idiopathic basal ganglia calcification | AD | SLC20A2, XPR1 |
| White matter and others | ||
| Agenesis of the corpus callosum with peripheral neuropathy | AR | SLC12A6 |
| Leukodystrophy and acquired microcephaly with or without dystonia | AR | PLEKHG2 |
| Nonsyndromic hydrocephalus | AR | CCDC88C, MPDZ |
| Porencephaly | AD | COL4A2 |
| Schizencephaly | UN | EMX2 |
| General brain malformation | ||
| Lissencephaly | AD | TUBA1A |
| AR | LAMB1, RELN | |
| XL | ARX, DCX | |
| UN | PAFAH1B1 | |
| Lissencephaly with cerebellar hypoplasia | AR | CDK5 |
| Lissencephaly with microcephaly | AR | KATNB1, NDE1 |
| Epilepsy, hearing loss, and mental retardation syndrome | AR | SPATA5 |
| Galloway-Mowat syndrome | AR | WDR73 |
| Mental retardation and microcephaly with pontine and cerebellar hypoplasia | XLD | CASK |
| Microcephaly-capillary malformation syndrome | AR | STAMBP |
| Microcephaly, epilepsy, and diabetes syndrome | AR | IER3IP1 |
| Microcephaly, seizures, and developmental delay | AR | PNKP |
| Microcephaly, short stature, and impaired glucose metabolism | AR | PPP1R15B, TRMT10A |
| Microcephaly, short stature, and polymicrogyria with seizures | AR | RTTN |
| Microcephaly with or without chorioretino-pathy, lymphedema, or mental retardation | AD | KIF11 |
| Postnatal progressive microcephaly, seizures, and brain atrophy | AR | MED17 |
| Primary microcephaly | AR | ANKLE2, ASPM, CENPE, CENPJ, MFSD2A, SASS6 |
| Primary microcephaly with or without cortical malformations | AR | WDR62 |
| Progressive microcephaly with seizures and cerebral and cerebellar atrophy | AR | QARS |
| Seizures, cortical blindness, microcephaly syndrome | AR | DIAPH1 |
| Macrocephaly, dysmorphic facies, and psychomotor retardation | AR | HERC1 |
| Polyhydramnios, megalencephaly, and symptomatic epilepsy | UN | STRADA |
| X-linked epilepsy with variable learning disabilities and behavior disorders | XLD, XLR | SYN1 |
| Psychomotor retardation, epilepsy, and craniofacial dysmorphism | AR | SNIP1 |
Bold italics, with multiple epilepsy phenotypes. ARX is associated with early infantile epileptic encephalopathy (XLR) and lissencephaly (XL). RELN is associated with familial temporal lobe epilepsy (AD) and lissencephaly (AR).
AD, autosomal dominant; AR, autosomal recessive; UN, unknown; XL, X-linked; XLD, X-linked dominant; XLR, X-linked recessive.
a Seizures may be infrequent.
From the gene-function point of view (Table 4), enzyme/enzyme modulator genes represent a large fraction of neurodevelopment-associated epilepsy genes (24/73), suggesting that these genes play a significant role in neurodevelopment and epileptogenesis. Genes encoding cytoskeletal molecules appeared also frequently (15/73). The remaining genes are involved in cell adhesion, extracellular matrix, membrane structure, membrane trafficking, or other unknown functions. In contrast, we did not come across any ion-channel gene. These data may further our knowledge on the pathogenic mechanisms of neurodevelopment and epilepsies.
Table 4Functional categories of the neurodevelopment-associated epilepsy genes.
| Encoded protein function | Gene |
|---|---|
| Enzyme/Enzyme modulator | |
| Enzyme | AMPD2, CASK, CDK5, EXOSC3, FIG4, HERC1, KATNB1, NSDHL, PAFAH1B1, PIK3R2, PNKP, QARS, SEPSECS, STAMBP, TRMT10A, TSEN15, TSEN2, TSEN54 |
| Enzyme modulator | ARFGEF2, CCDC88C, OPHN1, PLEKHG2, PPP1R15B, TSC2 |
| Transporter/Receptor | |
| Transporter | MFSD2A, SLC12A6, SLC20A2, SPATA5 |
| Receptor | GPR56, PTCH1, XPR1 |
| Cell adhesion molecule | CNTNAP2 |
| Extracellular matrix | COL4A2, LAMB1, LAMC3, RELN |
| Membrane structure | OCLN |
| Membrane trafficking | SYN1 |
| Cytoskeletal protein | CENPE, CENPJ, DCX, DIAPH1, FLNA, KIF11, KIF2A, KIF5C, PCLO, TUBA1A, TUBA8, TUBB2A, TUBB2B, TUBB3, TUBG1 |
| Nucleic acid binding | ARX, CLP1, EMX2 |
| Unclassified | ANKLE2, ASPM, ATN1, ERMARD, IER3IP1, MED17, MPDZ, NDE1, RTTN, SASS6, SNIP1, SRPX2, STRADA, TSC1, VPS53, WDR62, WDR73 |
3.3 Epilepsy-related genes
From the OMIM database, 536 genes were recognized as epilepsy-related genes. These genes are associated with diseases presenting gross physical, or other systemic, abnormalities that are accompanied by epilepsy or seizures. For example, the FMR1 gene defect causes Fragile X Syndrome which may be accompanied by seizures. However, the distinct features of Fragile X Syndrome are the intellectual disability, behavioral abnormalities, and physical alterations (such as an elongated face and large, or protruding, ears).
Epileptic seizures may occur in numerous genetic diseases (Table 5) including those that directly affect the cerebral neurons, such as the neuronal ceroid lipofuscinosis, in which epileptic seizure is a prominent feature; and those that may be indirectly related to brain function, such as the spinal muscular atrophy, in which epileptic seizure is inconstant. The characteristic clinical features of these disorders, beside epilepsy, usually provide useful clues for the clinical diagnosis and prompt for further genetic tests.
Table 5Epilepsy-related genes.
| Phenotype | Inheritance | Gene |
|---|---|---|
| Circulation disorder | ||
| Cavernous malform-ations | AD | CCM1, KRIT1 |
| Long QT syndrome | AD | CALM2, KCNQ1, KCNJ5 |
| UN | CAV3 | |
| Moyamoya disease | AR | GUCY1A3 |
| UN | RNF213 | |
| Others (cerebral amyl-oid angiopathy, etc.) | AD | COL4A1, PRNP, PROS1 |
| AR | CTC1, F2, JAM3 | |
| Cognitive disorder | ||
| Alzheimer disease | AD | APP, PSEN1, PSEN2 |
| Angelman syndrome | UN | UBE3A (IC) |
| Autism | AD | CHD8 |
| XLR | TMLHE | |
| UN | RPL10, SLC9A9 | |
| Fragile X syndrome | XLD | FMR1 |
| Frontotemporal dementia | AD | MAPT |
| Mental retardation | AD | ARID1A, ARID1B, ASXL1, AUTS2, BRAF, DEAF1, DYNC1H1, GNB1, HIVEP2, KAT6A, KIAA0442, KIF1A, MBD5, MED13L, MYT1L, NONO, PPP2R1A, PPP2R5D, PURA, SETBP1, SMARCA2, SMARCA4, SMARCB1, SMARCE1, SYNGAP1, TCF4, ZEB2 |
| AR | ANK3, ERCC6, FMN2, FTO, GRIK2, HERC2, KPTN, LMAN2L, MAN1B1, MED25, METTL23, NRXN1, PGAP1, PIGG, PUS3, SOBP, TRAPPC9 | |
| XLD | IQSEC2, SLC9A6, SYP, USP9X, ZDHHC15 | |
| XLR | AP1S2, ATP6AP2, CLIC2, CUL4B, DLG3, FGD1, GRIA3, HCFC1, IL1RAPL1, KDM5C, KIF4A, MECP2, MID2, PAK3, PHF6, RAB39B, SMS, TAF1, THOC2, UBE2A | |
| UN | CACNG2, COL4A3BP, DYRK1A, FTSJ1, GATAD2B, GDI1, GPT2, GRIN1, MEF2C (IC), SHROOM4 | |
| Others (McLeod syndrome, progressive encephalopathy, etc.) | AD | RAI1 (IC), SERPINI1 |
| AR | BSCL2 | |
| XL | XK | |
| UN | MTOR | |
| Developmental disorder (with physical malformation) | ||
| Congenital disorder of glycosylation | AR | ALG1, ALG11, ALG2, ALG3, ALG6, CAD, COG4, COG6, DOLK, DPAGT1, DPM1, DPM2, MOGS, MPDU1, NGLY1, RFT1, SLC39A8, STT3A, STT3B |
| XLD, SMo | SLC35A2 | |
| XLR | SSR4 | |
| UN | ALG12, ALG9, COG7, COG8 | |
| Joubert syndrome | AR | AHI1, CC2D2A, CSPP1 |
| UN | OFD1 | |
| Microphthalmia | AD | BMP4, OTX2, RBP4, SOX2 |
| XL | NAA10 | |
| Multiple congenital anomalies-hypotonia-seizures syndrome | AR | PIGN |
| AD, SMu; AR | PIGT | |
| XLR | PIGA | |
| Muscular dystrophy | AR | CHKB, LAMA2, TRAPPC11 |
| Muscular dystrophy-dystroglycanopathy | AR | B3GNT1, B4GAT1, FKTN, GMPPB, POMGNT1, POMK, POMT1, POMT2 |
| Neurofibromatosis | AD | NF1 |
| Neuropathy | AD | DNMT1, SPTLC2 |
| AR | ABHD12 | |
| Rett syndrome | UN | FOXG1 (IC) |
| Spinal muscular atrophy with progressive myo-clonic epilepsy | AR | ASAH1 |
| Sturge–Weber syndrome | UN | GNAQ |
| Zellweger syndrome | AR | PEX2 |
| UN | PEX13, PEX14, PEX19, PEX3 | |
| Others (craniosynost-osis, thanatophoric dysplasia, etc.) | AD | ACTB, ACTG1, ACVR1, ADNP, DNMT3A, EFTUD2, EHMT1 (IC), FAM111A, FGFR2, FGFR3, GATA6, HNF1B, KCNH1, KCNJ6, KMT2A, MAF, MAGEL2, MAPRE2, MARCA2, MSX2, NOTCH1, NSD1, POGZ, PTEN, PUF60, SATB2, SETD2, SOX5, ZSWIM6 |
| AR | AGPS, ALDH18A1 (IC), AP3D1, ARNT2, ATP6V0A2, BRAT1, C12orf57, C19orf61, CCDC88A, CEP164, CLPP, COL18A1, CRB2, CRLF1, DHCR24, DOCK6, EPG5, EXT2, FAT4, GNPAT, GPSM2, GPX4, LRP2, MKS1, NANS, NIN, PARN, PEX5, PIGL, RAB18, RAPSN, ROGDI, SLC33A1, SLC35A3, TELO2, XPNPEP3 | |
| XLD | AMER1, DXS423E, NDUFB11, NHS, SMC1A | |
| XLR | BCAP31, CHRDL1, DKC1, EBP, MBTPS2, PQBP1, RBM10, ZC4H2 | |
| UN | CEP290, CHN1, KRAS, NDN (IC), NRAS, SHANK3 (IC), SNRPN (IC) | |
| Inflammation and immune disorder | ||
| Herpes simplex ence-phalitis | AD | IRF3 |
| UN | TICAM1, TRAF3 | |
| Immunodeficiency | AR | BCL10, CORO1A, IFNAR2, ISG15, ORAI1, PGM3, PRKDC, STAT1, STAT2 |
| XLR | ATP6AP1 | |
| Inflammatory disorder | AD | IFIH1, NOD2 |
| AR | CD59, PSMB8 | |
| Others (candidiasis, neutropenia, etc.) | AD | RANBP2 |
| AR | CARD9, DOCK8, FADD, HAX1 | |
| AD, AR | CPT2 | |
| Metabolic disorder | ||
| Aciduria | AR | ACADSB, AUH, C2orf25, CLPB, CTH, D2HGDH, DHTKD1, DPYS, GLYCTK, MMAA, MMADHC, MTR, SLC25A1 |
| UN | ACSF3, IDH2 | |
| Amino acid metabolic disturbance | AR | AASS, ALDH4A1, AMT, ARG1, GCH1, GLDC, GLUL, LIAS, PRODH, QDPR, SLC25A15 |
| Coenzyme Q10 deficiency | AR | COQ2, COQ4, COQ6, COQ8A, COQ9, PDSS2 |
| Combined oxidative phosphorylation deficiency | AR | CARS2, EARS2, FARS2, GFM1, GTPBP3, MRPS22, MTFMT, MTO1, NARS2, RMND1, TXN2, VARS2 |
| XLR | AIFM1 | |
| Diabetes mellitus | AD | ABCC8, KCNJ11 |
| UN | ZFP57 | |
| Enzymatic deficiency | AD | ATP1A2, RYR1 |
| AR | ABAT, ACADS, ACOX1, ACY1, ADK, ADSL, AMACR, ASNS, ATIC, BCKDHA, CPS1, DHFR, DLD, DPYD, FAR1, HIBCH, MCCC1, MCCC2, MLYCD, MTHFR, NADK2, OPLAH, PC, PDHX, PDX1, PHGDH, PSAP, PSAT1, PSPH, SCO2, SLC25A20, UPB1 | |
| XLD | HSD17B10, PDHA1 | |
| XLR | GK, MAOA, NDP, OTC, PGK1 | |
| UN | BCKDK, HADHA, HMGCS2, NAT8L, PEX7, POMC | |
| Folate malabsorption | AR | SLC46A1 |
| Folate transport deficiency | AR | FOLR1 |
| Glycogen storage disease | AR | AGL, GYS1 |
| Hormone metabolism dysfunction | AD | CACNA1D, GLI2, PROK2, THRB |
| AR | MCM8, MRAP | |
| AD, AR | HESX1 | |
| XLR | AVPR2 | |
| XL | ANOS1 | |
| UN | FGF8 | |
| Hyperphosphatasia with mental retardation syndrome | AR | PGAP2, PGAP3, PIGO, PIGV, PIGW, PIGY |
| Hypocalcemia | AD | GNA11 |
| Hypoglycemia | AD | AKT2, GCK, INSR |
| Hypomagnesemia | AR | TRPM6 |
| AD, AR | CNNM2 | |
| UN | EGF | |
| Hypoparathyroidism | AD | PTH |
| Leigh syndrome | AR | LRPPRC |
| AR, Mi | NDUFA2, NDUFAF6, NDUFS4, NDUFS8 | |
| Lipid storage disorder | AR | NPC1, NPC2 |
| Menkes disease | XLR | ATP7A |
| Mitochondrial disease (progressive external ophthalmoplegia with mitochondrial DNA deletions, etc.) | AD | POLG2 |
| AR | ATP5A1, ATPAF2, BCS1L, BOLA3, BRP44L, C10orf2, FBXL4, MPC1, PNPLA8, POLG, RRM2B, RTN4IP1, SDHD, SUCLA2, TMEM70, UQCC2 | |
| AR, Mi | APOPT1, COX10, COX6B1, COX8A, FASTKD2, PET100 | |
| AR, XLD, Mi | FOXRED1, NDUFA1, NDUFAF3, NDUFV1, NUBPL | |
| Mucopolysaccharidosis | AR | HGSNAT |
| XLR | IDS | |
| Neuronal ceroid lipofuscinosis | AD | DNAJC5 |
| AR | CLN3, CLN5, CLN6, CLN8, CTSD, CTSF, GRN, MFSD8, PPT1, TPP1 | |
| Thiamine metabolism dysfunction syndrome | AR | SLC19A3, TPK1 |
| Vitamin D-dependent rickets | AR | CYP27B1 |
| Others (brain iron accumulation, Salla disease, etc.) | AD | ANKH, COL3A1, DNM1L, TTR |
| AR | ARHGDIA, CYB5R3, ECM1, ETFDH, ETHE1, GAMT, GBA, HADHB, HEXA, HSD17B4, KCNJ10, LARS2, MOCS2, PIGM, PLA2G6, SLC17A5, TANGO2 | |
| AD, AR | FTL, SLC16A1 | |
| XLD | WDR45 | |
| XLR | SLC6A8 | |
| UN | GPHN | |
| Movement disorder | ||
| Cerebellar ataxia | AD | CAMTA1 |
| AR | SLC9A1 | |
| Dyskinesia | AR | PDE10A |
| Dystonia | AD | SGCE |
| AR | ACO2, CRYAB, NALCN, TBCK, UNC80 | |
| AD, AR | GLRA1, SPR | |
| Episodic ataxia | AD | KCNA1 |
| UN | SLC1A3 | |
| Episodic hemiplegia | AD | ATP1A3 |
| Huntington disease | AD | HTT |
| Parkinson disease | AD | LRRK2 |
| AR | DNAJC6, SYNJ1 | |
| Spastic ataxia | AR | AFG3L2, SACS |
| Spastic paraplegia | AD | NIPA1 |
| AR | AP4B1, AP4E1, AP4S1, ERLIN2, GJC2, HACE1, TECPR2, ZFYVE26 | |
| XLR | PLP1 | |
| Spastic quadriplegia | AR | ADD3, ELOVL4, GAD1, SLC1A4 |
| Spinocerebellar ataxia | AD | ATXN10, ITPR1, TBP |
| AR | ANO10, GRM1, RUBCN, SNX14, SYT14, TDP2 | |
| UN | TDP1 | |
| Myelinating disorder | ||
| Alexander disease | AD | GFAP |
| Krabbe disease | AR | GALC |
| Leukodystrophy | AD | TUBB4A |
| AR | AIMP1, ARSA, HSPD1, POLR3B, VPS11 | |
| Leukoencephalopathy | AD | CSF1R |
| AR | DARS2, EIF2B1, HEPACAM, MLC1, RNASET2 | |
| Neoplastic disorder | ||
| Glioblastoma | AR | BRCA2 |
AD, autosomal dominant; AR, autosomal recessive; IC, isolated cases; Mi, mitochondrial; SMo, somatic mosaicism; SMu, somatic mutation; UN, unknown; XL, X-linked; XLD, X-linked dominant; XLR, X-linked recessive.
3.4 Potential epilepsy-associated genes
We found 247 additional genes by crosschecking our findings with those from the HGMD and the EpilepsyGene databases and 37 more genes by searching through recent publications (Table 6). These genes are reported to be potentially associated with epilepsy; however, they are currently not present in the OMIM database. Their associations with epilepsy warrant further verification in most of the cases. For instance, CUX1 and MCM9 were listed in the EpilepsyGene database. Mutations in CUX1, MCM9, and KCNT1 were identified in a patient with malignant migrating partial seizures of infancy. KCNT1 is an epilepsy gene and the KCNT1 mutation (c.2800G>A, p.Ala934Thr) identified in this patient has been experimentally proved to cause functional alternations [
[24]
]. Thus, the role of CUX1 and MCM9 in epilepsy has been questioned. In contrast, mutations in some genes, such as SCN3A, GABRA6, and KCNH5, have been repeatedly reported in patients with epilepsy [25
, 26
, 27
, 28
, 29
, 30
], and functional alterations induced by these mutations have been experimentally confirmed [26
, 28
, 30
].Table 6Potential epilepsy-associated genes.
| Encoded protein function | Gene |
|---|---|
| Ion channel | |
| Sodium channel | SCN3A, SCN4A, SCN5A |
| Potassium channel | KCNAB1, KCNAB2, KCNC3, KCND2, KCND3, KCNE1, KCNH2, KCNH5, KCNJ2, KCNMB3, KCNN3, KCNV2, KCTD3 |
| HCN channel | HCN2, HCN4 |
| Calcium channel | CACNA1G, CACNA2D1, CACNA2D2, RYR3, TRPM1 |
| Chloride channel | CLCN4, CLCN6 |
| GABA-A receptor | GABRA6, GABRB2 |
| NMDA receptor | GRIK1, GRINA |
| Acetylcholine receptor | CHRFAM7A, CHRNA7, CHRNB3 |
| Enzyme/Enzyme modulator | |
| Enzyme | ACMSD, ACOT7, ADAM22, AKT3, CBL, CHD1L, CHD3, CHD4, COX1, COX3, CP, CSNK1G1, CYP26C1, DGKD, DNM3, FASN, FBXO28, GBE1, HCK, HDAC4, HECW2, HS2ST1, HUWE1, INPP4A, KARS, KDM6A, KIAA1456, MAGI2, MAN2A2, MANBA, MAPK10, MCM9, ME2, MPP7, MRI1, MTMR11, ND1, ND4, ND5, NEDD4, NEDD4L, NEU1, OPA1, PARK2, PHF8, PIGQ, PNPT1, PRKX, PTPN23, SGK223, ST8SIA2, STK11, TK2, TNK2, TRIM8, TRMT44, UBR5, WHSC1, ZMYND8 |
| Enzyme modulator | ARHGEF15, ELMO1, FARP2, FSTL5, NOL3, NPRL2, NPRL3, PPP1R3C, RANGAP1, RAPGEF6, SRGAP2 |
| Transporter/receptor | |
| Transporter | AAAS, ATP13A2, ATP6, ATP6V0C, ATP8, ATP8A2, NIPA2, OCA2, SLC1A1, SLC25A2, SLC26A1, SLC30A3, SLC4A10, SLC4A3, SLC6A3, SLC6A4, SLC7A11, SLC8A1, SLCO1B7, TAP1 |
| Receptor | ADORA2A, AGTR2, CD46, CRHR1, CXCR4, ENG, EPHA5, EPHB2, ERBB4, FLT4, GABBR1, GABBR2, HTR1A, HTR2A, IL27RA, LPHN2, NPC1L1, NR2F1, OPRM1, OR10H2, PLXNB2, RORB, RTN4R, TRNR1, TSPAN7 |
| Transmembrane receptor regulatory/adaptor | DLG2, GIPC1 |
| Extracellular matrix | COL2A1, COL6A2, COL6A3, HSPG2, MATN4, NID1, TNFAIP6 |
| Cell adhesion molecule | CELSR3, CHL1, CTNND2, L1CAM, NLGN1, PCDH12, PCDH15, PCDH7, PCDHB13, PCDHB4, PCDHG |
| Signaling molecule | BDNF, BMP5, CRH, IL10, IL1B, IL1RN, IL6, NRG2, NRG3, PDYN, SEMA5B |
| Signal transduction | CALN1, CLSTN1 |
| Membrane structure | GJD2, LOR, PMP22 |
| Membrane trafficking | EXOC6B, NAPB, SEC24D, SNAP25, SV2A, SYN2, SYT2, TSNARE1, VPS35 |
| Surfactant protein | SUCO |
| Cytoskeletal protein | DMD, GAS2L2, HIP1, KIF3C, MYH14, MYH6, MYO9B, NEB, SVIL, TBCD, TUBA3E |
| Nucleic acid binding | BRD2, CELF4, CENPW, CREBBP, CUX1, DMBX1, EFTUD2, EIF2C4, EIF3E, GMEB2, HNRNPH1, HNRNPU, HOXD, INO80, JRK, KLF13, MED12, MLLT3, MSC, MYOCD, PHOX2B, RBFOX1, RBFOX3, RBPJ, RFX3, SCA2, SCNM1, SETD5, SON, THAP1, YAP1, ZBTB18, ZMYND11, ZNF12, ZNF182, ZNF44 |
| Chaperone | TBCD, TOR1A |
| Transfer/carrier | APOE4, CYTB, KPNA7, WDR19 |
| Defence/immune | C3, IGSF8 |
| Unclassified | BRWD3, BSN, C16orf62, C18orf25, C7orf55, DIP2C, FLG, GRIP1, HEG1, ITGB1BP1, KIAA2022, LRFN5, NCKAP5, NELL1, NGFRAP1, NKAIN3, NOL11, PIK3AP1, PODXL, PRICKLE2, PRRC2B, RB1, RD3, SEZ6, SHANK1, SKI, SLC7A6OS, SQSTM1, ST5, ST7, STYXL1, TBL1XR1, TENM2, TMEM139, TSPYL4, TTN, YWHAE, ZFYVE20 |
Bold italics, with multiple functional classifications.
4. Discussion
Here, we review all genes potentially associated with epilepsy, and present a summary of these genes according to the manifestation of epilepsy in the phenotype. These genes include epilepsy genes, neurodevelopment-associated epilepsy genes, and epilepsy-related genes. These integrated data represent a framework of epilepsy-associated genes that may be used for the following: (1) considering genetic tests in clinical practice and (2) evaluating the results of these tests. However, we must acknowledge that an endeavour such as this runs the risk of being incomplete, since there continue to be identification of novel epilepsy-associated genes in the following days.
Eighty-four genes have been considered as epilepsy genes. However, it should be noted that although these genes are associated with epilepsies, the pathogenic role played by each gene may differ according to the phenotype. For instance, both SCN1A and SCN9A are reported to be associated with the Dravet syndrome. Mutations in SCN1A are responsible for approximately 70–80% of the cases with Dravet syndrome [
2
, 20
, 31
], and the genotype (funotype)-phenotype correlations have been documented [[2]
]. In contrast, SCN9A may play a minor role and was suggested as a modifier gene in Dravet syndrome [[32]
]. Generally, an epileptic syndrome may have several genetic causes. Idiopathic epilepsies are believed to be caused by genetic abnormalities. Mutations in several genes have been identified in idiopathic epilepsies, such as GABRG2, GABRB3, CACNA1H, and GABRA1 in childhood absence epilepsy. However, the pathogenic role of each gene in idiopathic epilepsy warrants further experimental and clinical studies. From a practical point of view, except few genes like SCN1A, the frequency of gene mutation in an epileptic syndrome was not determined for most of the epilepsy genes. On the other hand, it has been frequently observed that an epilepsy gene may lead to several phenotypes, i.e., a spectrum of phenotype. Theoretically, due to the distinct function of the gene, phenotypes within the spectrum would share features in common, typically shown in the spectrum of epilepsy caused by SCN1A mutations. SCN1A mutations are associated with Dravet syndrome, partial epilepsy with antecedent febrile seizures, and generalized epilepsies with febrile seizures plus. The antecedent febrile seizure is the common feature in most of the cases and is a critical clue in clinical diagnosis and management [2
, 33
].Seventy-three genes have been considered as neurodevelopment-associated genes and 536 genes have been listed as epilepsy-related genes. The apparent neurodevelopmental malformation and gross physical or systemic abnormalities accompanied would provide critical evidences for the diagnosis and clues for designing cost-effective genetic-testing strategy for a specific target patient population. Two hundred and eighty-four genes are putatively associated with epilepsy. Although further verifications are required, new epilepsy genes are expected to be identified. The present summary of gene functions and their associations with epilepsy will serve as the basis for considering future studies, and it will further our understanding of the underlying genetic mechanisms of epilepsy.
Conflicts of interest
All authors declare that they have no conflicts of interest concerning this article.
Acknowledgements
This work was supported by Omics-based precision medicine of epilepsy being entrusted by Key Research Project of the Ministry of Science and Technology of China . (Grant No. 2016YFC0904400 ), the National Natural Science Foundation of China (grant Nos. 81271434 , 81301107 , 81571273 , 81571274 , 81501124 and 81501125 ), the Natural Science Foundation of Guangdong Province (grant Nos. 2014A030310094 and 2014A030313489 ), Science and Technology Project of Guangdong Province (grant No. 2013B051000084 ) Department of Education of Guangdong Province (grant Nos. 2013CXZDA022 , 2013KJCX0156 and 2012KJCX009 ), Foundation for High-level Talents in Higher Education of Guangdong (grant No. 2013-167 ), Yangcheng Scholar Research Project of Guangzhou Municipal College (grant Nos. 12A016S and 12A017G ), Science and Technology Project of Guangzhou (grant Nos. 2014J4100069 , 201508020011 , 201604020161 , and 201607010002 ), the Cultivation and Innovation Fund of Jinan University (grant No. 21615334 ) and Collaborative Innovation Center for Neurogenetics and Channelopathies . The funders had no role in study design, data collection and analysis, and decision to publish or preparation of the manuscript.
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Article Info
Publication History
Published online: December 06, 2016
Accepted:
November 30,
2016
Received in revised form:
November 3,
2016
Received:
September 30,
2016
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© 2016 Published by Elsevier Ltd on behalf of British Epilepsy Association.
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