Real-world utility of whole exome sequencing with targeted gene analysis for focal epilepsy

Driven by advances in genomic technology and reduction in costs, next-generation sequencing (NGS) is venturing into routine clinical care. The ‘real-world’ clinical utility of NGS remains to be determined in focal epilepsies, which account for 60% of all epilepsies and for which the importance of genetic factors is just beginning to emerge. We investigated the diagnostic yield and management implications of whole exome sequencing (WES)-based screening of selected genes in the routine care of common focal epilepsies suspected to have a genetic basis. We performed WES, followed by targeted analysis of 64 epilepsy genes, on 40 consecutive children and adults enrolled prospectively from routine clinical practice who had MRI-negative focal epilepsy and a family history of febrile seizures or any type of epilepsy in at least one first- or second-degree relative. Exclusion criteria were previous genetic testing, severe intellectual disability and benign focal epilepsies of childhood. 5/40 (12.5%) patients had a pathogenic or likely pathogenic variant, detected in SCN1A, DEPDC5, PCDH19, GABRG2 or NPRL2. Identifying a pathogenic SCN1A variant in a patient with drug-resistant epilepsy prompted to halt presurgical investigations due to concern of unfavorable post-surgical outcome. It also led in the same patient to discontinue long-standing carbamazepine therapy (a potentially aggravating drug in epilepsies due to SCN1A mutations), resulting in complete seizure control. Patients with pathogenic or likely pathogenic variants had a younger median age of seizure onset (range) compared to those without [18 months (8 months-18 years) vs 18 years (18 months-70 years), p = 0.02]. Our data demonstrate that WES with targeted gene analysis is an effective diagnostic tool for patients with common focal epilepsies in whom a genetic etiology is suspected. It can also influence clinical decision-making, including antiepileptic drug selection and consideration of epilepsy surgery, hence supporting its incorporation in the routine clinical care of this patient group.