Exome sequencing followed by large-scale genotyping fails to identify single rare variants of large effect in idiopathic generalized epilepsy.

Idiopathic generalized epilepsy (IGE) is a complex disease with high heritability, but little is known about its genetic architecture. Rare copy-number variants have been found to explain nearly 3% of individuals with IGE; however, it remains unclear whether variants with moderate effect size and frequencies below what are reliably detected with genome-wide association studies contribute significantly to disease risk. In this study, we compare the exome sequences of 118 individuals with IGE and 242 controls of European ancestry by using next-generation sequencing. The exome-sequenced epilepsy cases include study subjects with two forms of IGE, including juvenile myoclonic epilepsy (n = 93) and absence epilepsy (n = 25). However, our discovery strategy did not assume common genetic control between the subtypes of IGE considered. In the sequence data, as expected, no variants were significantly associated with the IGE phenotype or more specific IGE diagnoses. We then selected 3,897 candidate epilepsy-susceptibility variants from the sequence data and genotyped them in a larger set of 878 individuals with IGE and 1,830 controls. Again, no variant achieved statistical significance. However, 1,935 variants were observed exclusively in cases either as heterozygous or homozygous genotypes. It is likely that this set of variants includes real risk factors. The lack of significant association evidence of single variants with disease in this two-stage approach emphasizes the high genetic heterogeneity of epilepsy disorders, suggests that the impact of any individual single-nucleotide variant in this disease is small, and indicates that gene-based approaches might be more successful for future sequencing studies of epilepsy predisposition.

Genome-wide mapping for clinically relevant predictors of lamotrigine- and phenytoin-induced hypersensitivity reactions.

AIMS: An association between carbamazepine-induced hypersensitivity and HLA-A*3101 has been reported in populations of both European and Asian descent. We aimed to investigate HLA-A*3101 and other common variants across the genome as markers for cutaneous adverse drug reactions (cADRs) attributed to lamotrigine and phenytoin. MATERIALS & METHODS: We recruited patients with lamotrigine-induced cADRs (n = 46) and patients with phenytoin-cADRs (n = 44) and the 1958 British birth cohort was used as a control (n = 1296). HLA-A*3101 was imputed from genome-wide association study data. We applied genome-wide association to study lamotrigine- and phenytoin-induced cADR, and total cADR cases combined. RESULTS: Neither HLA-A*3101 nor any other genetic marker significantly predicted lamotrigine- or phenytoin-induced cADRs. CONCLUSION: HLA-A*3101 does not appear to be a predictor for lamotrigine- and phenytoin-induced cADRs in Europeans. Our genome-wide association study results do not support the existence of a clinically relevant common variant for the development of lamotrigine- or phenytoin-induced cADRs. As a predictive marker, HLA-A*3101 appears to be specific for carbamazepine-induced cADRs.