Clinical application of trio-based whole-exome sequencing in idiopathic generalized epilepsy

Idiopathic generalized epilepsies (IGEs) are a common group of genetic generalized epilepsies with high genetic heterogeneity and complex inheritance. However, the genetic basis is still largely unknown. This study aimed to explore the genetic etiologies in IGEs.

Trio-based whole-exome sequencing was performed in 60 cases with IGEs. The pathogenicity of candidate genetic variants was evaluated by the criteria of the American College of Medical Genetics and Genomics (ACMG), and the clinical causality was assessed by concordance between the observed phenotype and the reported phenotype.

Seven candidate variants were detected in seven unrelated cases with IGE (11.7%, 7/60). According to ACMG, a de novo SLC2A1 (c.376C>T/p.Arg126Cys) variant identified in childhood absence epilepsy was evaluated as pathogenic with clinical concordance. Six variants were assessed to be uncertain significance by ACMG, but then considered causative after evaluation of clinical concordance. These variants included CLCN4 hemizygous variant (c.2044G>A/p.Glu682Lys) and IQSEC2 heterozygous variant (c.4315C>T/p.Pro1439Ser) in juvenile absence epilepsy, EFHC1 variant (c.1504C>T/p.Arg502Trp) and CACNA1H (c.589G>T/p.Ala197Ser) both with incomplete penetrance in juvenile myoclonic epilepsy, and GRIN2A variant (c.2011C>G/p.Gln671Glu) and GABRB1 variant (c.1075G>A/p.Val359Ile) both co-segregated with juvenile myoclonic epilepsy. Among them, GABRB1 was for the first time identified as potential novel causative gene for IGE.

Considering the genetic heterogeneity and complex inheritance of IGEs, a comprehensive evaluation combined the ACMG scoring and assessment of clinical concordance is suggested for the pathogenicity analysis of variants identified in clinical screening. GABRB1 is probably a novel causative gene for IGE, which warrants further studies.