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  • Title: Electrophysiological features: The next precise step for SCN2A developmental epileptic encephalopathy.
    Author: Miao P, Tang S, Ye J, Wang J, Lou Y, Zhang B, Xu X, Chen X, Li Y, Feng J.
    Journal: Mol Genet Genomic Med; 2020 Jul; 8(7):e1250. PubMed ID: 32400968.
    Abstract:
    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.
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