Tiered analysis of whole-exome sequencing for epilepsy diagnosis

It is thought that despite highly variable phenotypic expression, 70-80% of all epileptic cases are caused by one or more genetic mutations. Next generation sequencing technologies, such as whole exome sequencing (WES), can be used in a diagnostic or research setting to identify genetic mutations which may have significant prognostic implications for patients and their families. In this study, 398 genes associated with epilepsy or recurrent seizures were stratified into tiers based on genotype-phenotype concordance, tissue gene expression, frequency of affected individuals with mutations and evidence from functional and family studies. WES was completed on 14 DNA samples (2 with known mutations in SCN1A and 12 with no known mutations) from individuals diagnosed with epilepsy using an Ion AmpliSeq approach. WES confirmed positive SCN1A mutations in two samples. In n = 5/12 samples (S-3 to -14) we identified potentially causative mutations across five different genes. S-5 was identified to have a novel missense mutation in CCM2; S-6 a novel frameshift mutation identified in ADGRV1; S-10 had a previously reported pathogenic mutation in PCDH19, whilst a novel missense mutation in PCDH19 was shown in S-12; and S-13 identified to have separate missense mutations in KCNA2 and NPRL3. The application of WES followed by a targeted variant prioritization approach allowed for the discovery of potentially causative mutations in our cohort of previously undiagnosed epilepsy patients.