Is HLA-DRW13 (W6) associated with juvenile myoclonic epilepsy in Arab patients?

Genetic Landscape of Common Epilepsies: Advancing towards Precision in Treatment

Epilepsy, a neurological disease characterized by recurrent seizures, is highly heterogeneous in nature. Based on the prevalence, epilepsy is classified into two types: common and rare epilepsies. Common epilepsies affecting nearly 95% people with epilepsy, comprise generalized epilepsy which encompass idiopathic generalized epilepsy like childhood absence epilepsy, juvenile myoclonic epilepsy, juvenile absence epilepsy and epilepsy with generalized tonic-clonic seizure on awakening and focal epilepsy like temporal lobe epilepsy and cryptogenic focal epilepsy. In 70% of the epilepsy cases, genetic factors are responsible either as single genetic variant in rare epilepsies or multiple genetic variants acting along with different environmental factors as in common epilepsies. Genetic testing and precision treatment have been developed for a few rare epilepsies and is lacking for common epilepsies due to their complex nature of inheritance. Precision medicine for common epilepsies require a panoramic approach that incorporates polygenic background and other non-genetic factors like microbiome, diet, age at disease onset, optimal time for treatment and other lifestyle factors which influence seizure threshold. This review aims to comprehensively present a state-of-art review of all the genes and their genetic variants that are associated with all common epilepsy subtypes. It also encompasses the basis of these genes in the epileptogenesis. Here, we discussed the current status of the common epilepsy genetics and address the clinical application so far on evidence-based markers in prognosis, diagnosis, and treatment management. In addition, we assessed the diagnostic predictability of a few genetic markers used for disease risk prediction in individuals. A combination of deeper endo-phenotyping including pharmaco-response data, electro-clinical imaging, and other clinical measurements along with genetics may be used to diagnose common epilepsies and this marks a step ahead in precision medicine in common epilepsies management.

Immunogenetic predisposing factors for mesial temporal lobe epilepsy with hippocampal sclerosis

PURPOSE

Neuroinflammation appears as an important epileptogenic mechanism. Experimental and clinical studies have demonstrated an upregulation of pro-inflammatory cytokines such as IL-1β and TNF-α, in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). Expression of these cytokines can be modulated by polymorphisms such as rs16944 and rs1800629, respectively, both of which have been associated with febrile seizures (FS) and MTLE-HS development. The human leukocyte antigen (HLA) system has also been implicated in diverse epileptic entities, suggesting a variable role of this system in epilepsy. Our aim was to analyse the association between immunogenetic factors and MTLE-HS development. For that rs16944 (-511 T>C, IL-1β), rs1800629 (-308 G>A, TNF-α) polymorphisms and HLA-DRB1 locus were genotyped in a Portuguese Population.

METHODS

We studied 196 MTLE-HS patients (108 females, 88 males, 44.7 ± 12.0 years, age of onset = 13.6 ± 10.3 years, 104 with FS antecedents) and 282 healthy controls in a case-control study.

RESULTS

The frequency of rs16944 TT genotype was higher in MTLE-HS patients compared to controls (14.9% in MTLE-HS vs. 7.7% in controls, p = 0.021, OR [95% CI] = 2.20 [1.13-4.30]). This association was independent of FS antecedents. No association was observed between rs1800629 genotypes or HLA-DRB1 alleles and MTLE-HS susceptibility. Also, no correlation was observed between the studied polymorphisms and disease age of onset.

CONCLUSION

The rs16944 TT genotype is associated with MTLE-HS development what may be explained by the higher IL-1β levels produced by this genotype. High IL-1β levels may have neurotoxic effects or imbalance neurotransmission leading to seizures.

Dimorphism of TAP-1 gene in Caucasian with juvenile myoclonic epilepsy and in Tunisian with idiopathic generalized epilepsies

Juvenile myoclonic epilepsy (JME) is the most common form of idiopathic generalized epilepsies (IGE) that account for about 5-10% of all types of epilepsies. The first putative locus termed EJM1 is on the human leucocyte antigen (HLA-II) region of chromosome 6p21.3. Interestingly, the EJM1 region includes the Transporter associated with antigen processing 1 (TAP-1) gene encoding the TAP-1, and previous studies have reported associations between HLA-II polymorphisms and different types of epilepsy. In this study, we report an association between two TAP-1 functional polymorphisms the I333V and the D637G and most common IGE in Tunisian population, but we fail to find significant results in Caucasian with JME.

Advances in genetics of juvenile myoclonic epilepsies

One by one, mutation-containing mendelian genes that cause monogenic juvenile myoclonic epilepsies (JME) and single nucleotide polymorphisms (SNP)-susceptibility alleles that increase risks for nonmendelian complex JME should fall to the power of molecular genetics. Of 15 chromosome loci, 3 mendelian genes (alpha1-subunit of the GABA(A) receptor [GABRA1], chloride channel 2 gene [CLCN2], and Myoclonin1/EFHC1) and 2 SNP-susceptibility alleles of putative JME genes in epistases (bromodomain-containing protein 2 [BRD2] and connexin [Cx]-36) have been identified, so far. Antiepileptic drugs now can be designed against the specific molecular defects of JME.

The polymorphism GABABR1 T1974C[rs29230] of the GABAB receptor gene is not associated with the diagnosis of alcoholism or alcohol withdrawal seizures

As the inhibitory neurotransmitter gamma aminobutyric acid (GABA) modulates ethanol consumption, alcohol withdrawal symptoms and seizure generation by interacting with the GABAB receptor, the genes encoding for the GABAB receptor can be considered as candidate genes for alcoholism and alcohol withdrawal seizures (AWS). As the polymorphism GABABR1 T1974C[rs29230] of the GABAB receptor gene had been associated with alcoholism and EEG abnormalities in prior studies, the present examination investigated if the polymorphism is associated with the diagnosis of alcoholism or AWS. After genotyping the allele and genotype frequencies of a group of alcoholics with a history of AWS (n = 69) were compared with the results of a group of alcoholics with only mild withdrawal symptoms (n = 97). Additionally a group of healthy controls (n = 101) was compared with individuals with the diagnosis of alcoholism (n = 220). As no significant differences were found between the compared groups, this study gave no further evidence for GABABR1 T1974C[rs29230] as a candidate for alcoholism or AWS.

Recent Developments in the Quest for Myoclonic Epilepsy Genes

Understanding the latest advances in the molecular genetics of the epilepsies is important, as it provides a basis for comprehending the new practice of epileptology. Epilepsies have traditionally been classified and subtyped on the basis of clinical and neurophysiologic concepts. However, the complexity and variability of phenotypes and overlapping clinical features limit the resolution of phenotype-based classification and confound epilepsy nosology. Identification of tightly linked epilepsy DNA markers and discovery of epilepsy-causing mutations provide a basis for refining the classification of epilepsies. Recent discoveries regarding the genetics surrounding certain epilepsy types (including Lafora's progressive myoclonic epilepsy, the severe myoclonic epilepsy of infancy of Dravet, and idiopathic generalized epilepsies) may be the beginning of a better understanding of how rare Mendelian epilepsy genes and their genetic architecture can explain some complexities of the common epilepsies.

An association between mesial temporal lobe epilepsy with hippocampal sclerosis and human leukocyte antigens

PURPOSE

Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is one of the medically intractable epilepsies that may be remediable with surgery. Although the pathogenesis of HS still remains obscure, genetics may play a role as a predisposing factor, with the genetically controlled immune system as one of its aspects. Our aim in this study was to investigate whether there is any association between human leukocyte antigens (HLAs) that are related to chromosome 6 and this specific type of epilepsy.

METHODS

HLA class I and II typing were performed with the microlymphocytotoxicity method on 65 Turkish patients with MTLE-HS and on 184 healthy controls.

RESULTS

Our study revealed a significantly high frequency of class II antigens HLA-DQ2, -DR4, and -DR7 alleles and the combination of HLA-DR4-DQ2, and DR7-DQ2 alleles.

CONCLUSIONS

The HLA alleles that occur with increased frequency in many HLA- associated conditions appear to serve as risk factors that increase susceptibility but are not essential for disease expression. Our data support the role of genetic factors in the development of HS, possibly related to early childhood events that may act as a trigger factor to initiate the cascade in genetically prone patients with specific HLA types to give rise to MTLE eventually.

Reproducibility and complications in gene searches: linkage on chromosome 6, heterogeneity, association, and maternal inheritance in juvenile myoclonic epilepsy

Evidence for genetic influences in epilepsy is strong, but reports identifying specific chromosomal origins of those influences conflict. One early study reported that human leukocyte antigen (HLA) markers were genetically linked to juvenile myoclonic epilepsy (JME); this was confirmed in a later study. Other reports did not find linkage to HLA markers. One found evidence of linkage to markers on chromosome 15, another to markers on chromosome 6, centromeric to HLA. We identified families through a patient with JME and genotyped markers throughout chromosome 6. Linkage analysis assuming equal male-female recombination probabilities showed evidence for linkage (LOD score 2.5), but at a high recombination fraction (theta), suggesting heterogeneity. When linkage analysis was redone to allow independent male-female thetas, the LOD score was significantly higher (4.2) at a male-female theta of.5,.01. Although the overall pattern of LOD scores with respect to male-female theta could not be explained solely by heterogeneity, the presence of heterogeneity and predominantly maternal inheritance of JME might explain it. By analyzing loci between HLA-DP and HLA-DR and stratifying the families on the basis of evidence for or against linkage, we were able to show evidence of heterogeneity within JME and to propose a marker associated with the linked form. These data also suggest that JME may be predominantly maternally inherited and that the HLA-linked form is more likely to occur in families of European origin.

Association analysis of exonic variants of the gene encoding the GABAB receptor and idiopathic generalized epilepsy

The gene encoding the GABAB receptor (GABABR1) maps close to the HLA-F locus on chromosome 6p21.3 in the same region to which a major susceptibility locus for common subtypes of idiopathic generalized epilepsy (IGE), designated as EJM1, has been localized. Moreover, animal models suggest that the GABAB receptor plays a critical role in the epileptogenesis of absence seizures. Accordingly, the present association study tested the candidate gene hypothesis that genetic variants of the human GABABR1 gene confer susceptibility to common subtypes of IGE. Three DNA sequence variants in exons 1a1, 7, and 11 of the GABABR1 gene were assessed by PCR-based restriction fragment length polymorphisms in 248 unrelated probands of German descent, comprising 72 patients with juvenile myoclonic epilepsy (JME), 46 patients with idiopathic absence epilepsy (IAE), and 130 control subjects without a history of epileptic seizures and lack of generalized spike-wave discharges in their electroencephalogram. The results revealed no evidence for an allelic association of any of the GABABR1 sequence variants with either JME or IAE (P > 0.18). Thus, we failed to demonstrate that any of the three exonic GABABR1 variants themselves, or other so-far unidentified mutations, which are in strong linkage disequilibrium with the investigated variants, are involved in the pathogenesis of common IGE subtypes.

Family studies and human leukocyte antigen class II typing in Indian probands with seizures in association with single small enhancing computed tomography lesions

PURPOSE

To define the clinical features of the syndrome of seizures associated with single, small, enhancing computed tomography (CT) lesions (SSELs) in 235 Indian probands and seizure types among their family members. Human leukocyte antigen (HLA) class II genomic typing in randomly selected 41 probands was done to identify the role of hereditary factors in this syndrome.

METHODS

The seizure types among 235 probands, their clinical outcome, and seizures in their family members were studied. Family data were collected on relatives of 212 additional probands with neurologic diseases other than epilepsy. HLA class II antigens were studied by using polymerase chain reaction (PCR) amplified DNA and sequence-specific oligonucleotide probe (PCR-SSOP) hybridization.

RESULTS

The seizures in 86% were partial with or without generalization; 77% had fewer than five seizures before the first CT scan. Evanescent focal neurologic deficits after seizures were noted in 40%. Most patients (97%) were treated with a single antiepileptic drug (AED). Significant resolution of the CT scan lesion was noted within 6 months in 125 (53%) of 235 cases. Two thirds of patients had no seizures while taking a single AED, and an additional 18% had no seizures even after their AEDs were discontinued. Epilepsy among relatives of Indian probands having seizures in association with SSELs was more common as compared with relatives of probands with other neurologic diseases. A family history of seizures was noted in 21% probands, the ratio of affected first- to second-degree relatives was 4.3:1, and 60% of affected sibs had syndromic concordance with probands. There was a positive association of HLA-DRB1*13 (Pc = 0.036) with this syndrome.

CONCLUSIONS

The syndrome of seizures in association with SSELs seems to be a benign localization-related epileptic syndrome. Our results of HLA studies point to an inherited susceptibility to an infective agent, which in most cases is of cysticercal etiology.

Lack of association between juvenile myoclonic epilepsy and HLA-DR13

PURPOSE

We sought to replicate and extend a previously reported positive association between juvenile myoclonic epilepsy and HLA-DR13.

METHODS

Ninety-three subjects with juvenile myoclonic epilepsy and 93 normal blood donors, entirely of white origin with their families mostly of French extraction, underwent DNA-based HLA-DR13 and DQB6 typing.

RESULTS

None of the investigated alleles or combination of alleles (DRB1*1301-DQB1*0603 or DRB1*1302-DQB1*0604) showed a significant difference between patients and controls.

CONCLUSIONS

Unlike previously reported positive association, in this population, there is no evidence that susceptibility to juvenile myoclonic epilepsy is associated with HLA-DR13.

Epilepsy classification and factors associated with control in Saudi adult patients

There is insufficient information on the epilepsies in Saudi Arabia. The objectives were to classify the patients according to seizure types and epilepsies as well as to determine the factors associated with control. In a hospital-based study, clinical information, electroencephalographic and neuroimaging findings were utilized to classify the cases into seizure types and epilepsies according to ILAE criteria and to determine the factors statistically associated with control. In the study there were 826 patients (454 males and 372 females; mean age = 28.7 years; >80% below 30 years at onset). The seizure types were: generalized tonic-clonic (43.8%), partial seizure secondarily generalized (41.9%), myoclonic (8.4%), simple partial (1.3%), complex partial (1.3%) and absence (0.4%). About 15% of the classifiable epilepsies were symptomatic. Most symptomatic epilepsies occurred in people over the age of 50 years. One-year remission rate was 80% and the factors associated with control were: compliance, monotherapy, therapeutic drug level and seizure type. The results showed that epilepsy predominantly affected young adults and confirmed the association of partial epilepsy with clinical and CT abnormalities. The 1-year remission rate was comparable with reports from other studies as well as the factors associated with control in our patients.

The phenotypic spectrum related to the human epilepsy susceptibility gene "EJM1"

Linkage studies of families ascertained through patients with juvenile myoclonic epilepsy (JME) suggest that an HLA-linked susceptibility gene on chromosome 6, designated "EJM1," predisposes to a group of idiopathic generalized epilepsies (IGEs) comprising JME, juvenile absence epilepsy (JAE), childhood absence epilepsies (CAE), and epilepsies with generalized tonic-clonic seizures (GTCS). To explore the EJM1-related phenotypic spectrum, we conducted linkage studies with HLA-DQ alpha restriction fragment length polymorphisms in 44 families ascertained through patients with CAE or JAE. Our results for the entire group of families provide evidence against a major susceptibility locus for idiopathic absence epilepsies and broader spectra of IGEs in the HLA region. Lod scores less than -2 were obtained for a region from 10 cM up to 23 cM on either side of the HLA-DQ alpha locus, depending on the assumed trait model. Suggestive evidence for linkage was found only for a subgroup of families with JME patients assuming an autosomal dominant mode of inheritance with 70% penetrance. A maximum lod score was obtained when family members with JME, JAE, CAE, and idiopathic GTCS were included into the affection status. Our results demonstrate that (1) the genetic susceptibility to idiopathic absence epilepsies and broader spectra of IGEs is heterogeneous, (2) the gene effect of EJM1 depends on the familial genetic background, and (3) EJM1 confers genetic susceptibility to idiopathic absence epilepsies and broader spectra of IGEs in the presence of family members with JME.