Use of a Dynamic Genetic Testing Approach for Childhood-Onset Epilepsy

Importance: Although genetic testing is important for bringing precision medicine to children with epilepsy, it is unclear what genetic testing strategy is best in maximizing diagnostic yield. Objectives: To evaluate the diagnostic yield of an exome-based gene panel for childhood epilepsy and discuss the value of follow-up testing. Design, Setting, and Participants: A case series study was conducted on data from clinical genetic testing at Children's Hospital of Philadelphia was conducted from September 26, 2016, to January 8, 2018. Initial testing targeted 100 curated epilepsy genes for sequence and copy number analysis in 151 children with idiopathic epilepsy referred consecutively by neurologists. Additional genetic testing options were offered afterward. Exposures: Clinical genetic testing. Main Outcomes and Measures: Molecular diagnostic findings. Results: Of 151 patients (84 boys 55.6%; median age, 4.2 years interquartile range, 1.4-8.7 years), 16 children (10.6%; 95% CI, 6%-16%) received a diagnosis after initial panel analysis. Parental testing for 15 probands with inconclusive results revealed de novo variants in 7 individuals (46.7%), resulting in an overall diagnostic yield of 15.3% (23 of 151; 95% CI, 9%-21%). Twelve probands with nondiagnostic panel findings were reflexed to exome sequencing, and 4 were diagnostic (33.3%; 95% CI, 6%-61%), raising the overall diagnostic yield to 17.9% (27 of 151; 95% CI, 12%-24%). The yield was highest (17 of 44 38.6%; 95% CI, 24%-53%) among probands with epilepsy onset in infancy (age, 1-12 months). Panel diagnostic findings involved 16 genes: SCN1A (n = 4), PRRT2 (n = 3), STXBP1 (n = 2), IQSEC2 (n = 2), ATP1A2, ATP1A3, CACNA1A, GABRA1, KCNQ2, KCNT1, SCN2A, SCN8A, DEPDC5, TPP1, PCDH19, and UBE3A (all n = 1). Exome sequencing analysis identified 4 genes: SMC1A, SETBP1, NR2F1, and TRIT1. For the remaining 124 patients, analysis of 13 additional genes implicated in epilepsy since the panel was launched in 2016 revealed promising findings in 6 patients. Conclusions and Relevance: Exome-based targeted panels appear to enable rapid analysis of a preselected set of genes while retaining flexibility in gene content. Successive genetic workup should include parental testing of select probands with inconclusive results and reflex to whole-exome trio analysis for the remaining nondiagnostic cases. Periodic reanalysis is needed to capture information in newly identified disease genes.