De novo variants in KCNA3 cause developmental and epileptic encephalopathy

Objective Variants in several potassium channel genes, including KCNA1 and KCNA2 , cause Developmental and Epileptic Encephalopathies (DEEs). We investigated whether variants in KCNA3 , another mammalian homologue of the Drosophila shaker family and encoding for Kv1.3 subunits, can cause DEE. Methods Genetic analysis of study individuals was performed by routine exome or genome sequencing, usually of parent‐offspring trios. Phenotyping was performed via a standard clinical questionnaire. Currents from wild‐type and/or mutant Kv1.3 subunits were investigated by whole‐cell patch‐clamp upon their heterologous expression. Results Fourteen individuals, each carrying a de novo heterozygous missense variant in KCNA3 , were identified. Most (12/14; 86%) had DEE with marked speech delay with or without motor delay, intellectual disability, epilepsy, and autism spectrum disorder. Functional analysis of Kv1.3 channels carrying each variant revealed heterogeneous functional changes, ranging from “pure” loss‐of‐function (LoF) effects due to faster inactivation kinetics, depolarized voltage‐dependence of activation, slower activation kinetics, increased current inactivation, reduced or absent currents with or without dominant‐negative effects, to “mixed” loss‐ and gain‐of‐function (GoF) effects. Compared to controls, Kv1.3 currents in lymphoblasts from 1 of the proband displayed functional changes similar to those observed upon heterologous expression of channels carrying the same variant. The antidepressant drug fluoxetine inhibited with similar potency the currents from wild‐type and 1 of the Kv1.3 GoF variant. Interpretation We describe a novel association of de novo missense variants in KCNA3 with a human DEE, and provide evidence that fluoxetine might represent a potential targeted treatment for individuals carrying variants with significant GoF effects. ANN NEUROL 2024;95:365–376