Epilepsy With Myoclonic Atonic Seizures: Why Is the Yield of Genetic Testing for a “Presumed Genetic” Epilepsy Low?

Phenotypic and Genetic Spectrum of Epilepsy With Myoclonic Atonic Seizures Tang S, Addis L, Smith A, Topp SD, Pendziwiat M, Mei D, Parker A, Agrawal S, Hughes E, Lascelles K, Williams RE, Fallon P, Robinson R, Cross HJ, Hedderly T, Eltze C, Kerr T, Desurkar A, Hussain N, Kinali M, Bagnasco I, Vassallo G, Whitehouse W, Goyal S, Absoud M, EuroEPINOMICS-RES Consortium, Møller RS, Helbig I, Weber, YG, Marini C, Guerrini R, Simpson MA, Pal DK. Epilepsia. 2020;61(5):995-1007. doi: 10.1111/epi.16508 Objective: We aimed to describe the extent of neurodevelopmental impairments and identify the genetic etiologies in a large cohort of patients with epilepsy with myoclonic atonic seizures (MAEs). Methods: We deeply phenotyped patients with MAE for epilepsy features, intellectual disability, autism spectrum disorder, and attention-deficit/hyperactivity disorder using standardized neuropsychological instruments. We performed exome analysis (whole exome sequencing) filtered on epilepsy and neuropsychiatric gene sets to identify genetic etiologies. Results: We analyzed 101 patients with MAE (70% male). The median age of seizure onset was 34 months (range = 6-72 months). The main seizure types were myoclonic atonic or atonic in 100%, generalized tonic-clonic in 72%, myoclonic in 69%, absence in 60%, and tonic seizures in 19% of patients. We observed intellectual disability in 62% of patients, with extremely low adaptive behavioral scores in 69%. In addition, 24% exhibited symptoms of autism and 37% exhibited attention-deficit/hyperactivity symptoms. We discovered pathogenic variants in 12 (14%) of 85 patients, including 5 previously published patients. These were pathogenic genetic variants in SYNGAP1 (n = 3), KIAA2022 (n = 2), and SLC6A1 (n = 2), as well as KCNA2, SCN2A, STX1B, KCNB1, and MECP2 (n = 1 each). We also identified 3 new candidate genes, ASH1L, CHD4, and SMARCA2 in 1 patient each. Significance: MAE is associated with significant neurodevelopmental impairment. MAE is genetically heterogeneous, and we identified a pathogenic genetic etiology in 14% of this cohort by exome analysis. These findings suggest that MAE is a manifestation of several etiologies rather than a discrete syndromic entity.