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Background: To investigate the relationships among phenotypes, genotypes, and funotypes of SCN2A-related developmental epileptic encephalopathy (DEE)., Methods: We enrolled five DEE patients with five de novo variants of the SCN2A. Functional analysis and pharmacological features of Nav1.2 channel protein expressed in HEK293T cells were characterized by whole-cell patch-clamp recording., Results: The phenotypes of c.4712T>C(p. I1571T), c.2995G>A(p.E999K), and c.4015A>G(p. N1339D) variants showed similar characteristics, including early seizure onset with severe to profound intellectual disability. Electrophysiological recordings revealed a hyperpolarizing shift in the voltage dependence of the activation curve and smaller recovery time constants of fast-inactivation than in wild type, indicating a prominent gain of function (GOF). Moreover, pharmacological electrophysiology showed that phenytoin inhibited over a 70% peak current and was more effective than oxcarbazepine and carbamazepine. In contrast, c.4972C>T (p.P1658S) and c.5317G>A (p.A1773T) led to loss of function (LOF) changes, showing reduced current density and enhanced fast inactivation. Both showed seizure onset after 3 months of age with moderate development delay. Interestingly, we discovered that choreoathetosis was a specific phenotype feature., Conclusion: These findings provided the insights into the phenotype-genotype-funotype relationships of SCN2A-related DEE. The preliminary evaluation using the distinct hints of GOF and LOF helped plan the treatment, and the next precise step should be electrophysiological study., (© 2020 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.)

Epilepsy is a common and genetically heterogeneous disorder among children. Advances in next-generation sequencing have revealed that numerous epilepsy genes, helped us improve the understanding of mechanisms underlying epileptogenesis, and guided the development of treatments. We identified 39 candidate variants in 21 genes, including 37 that were pathogenic or likely pathogenic variants according to the American College of Medical Genetics and Genomics scoring system and two variants of uncertain significance that were considered causative after they were associated with clinical characteristics. Thirty were de novo variants (76.9%), and 20 variants had not previously been reported (51.3%). We obtained a diagnosis in 39 of the 141 probands (27.7%). The most frequently mutated gene was SCN1A; KCNQ2, KCNT1, PCDH19, STXBP1, SCN2A, TSC2, and PRRT2 were mutated in more than one individual; ANKRD11, CDKL5, DCX, DEPDC5, GABRB3, GRIN2A, IQSEC2, KCNA2, KCNB1, KCNJ6, TSC1, SCN9A, and SCN1B were mutated in a single individual. In addition, we detected a nonsense variant in a candidate gene KCND1 and considered it as a new candidate epilepsy gene, which needed further functional study. Consequently, large number of unreported variants were detected, diverse phenotypes were associated with known epilepsy genes. Changes in clinical management beyond genetic counseling were suggested., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)