OBJECTIVE: Heterozygous gain-of-function (GOF) variants in KCNQ2 and KCNQ3, encoding the voltage-gated potassium channel subunits Kv7.2 and Kv7.3, lead to neurodevelopmental disorders for which no established treatments are available. Amitriptyline, an antidepressant, blocks Kv7.2/Kv7.3 and has previously been reported to be effective in a single individual with a KCNQ2 GOF variant. We designed a retrospective, single-arm, multicenter study to investigate the effects of amitriptyline in …