Complete loss of KCNA1 activity causes neonatal epileptic encephalopathy and dyskinesia

BACKGROUND: Since 1994, over 50 families affected by the episodic ataxia type 1 disease spectrum have been described with mutations in KCNA1, encoding the voltage-gated K(+) channel subunit Kv1.1. All of these mutations are either transmitted in an autosomal-dominant mode or found as de novo events. METHODS: A patient presenting with a severe combination of dyskinesia and neonatal epileptic encephalopathy was sequenced by whole-exome sequencing (WES). A candidate variant was tested using cellular assays and patch-clamp recordings. RESULTS: WES revealed a homozygous variant (p.Val368Leu) in KCNA1, involving a conserved residue in the pore domain, close to the selectivity signature sequence for K(+) ions (TVGYG). Functional analysis showed that mutant protein alone failed to produce functional channels in homozygous state, while coexpression with wild-type produced no effects on K(+) currents, similar to wild-type protein alone. Treatment with oxcarbazepine, a sodium channel blocker, proved effective in controlling seizures. CONCLUSION: This newly identified variant is the first to be reported to act in a recessive mode of inheritance in KCNA1. These findings serve as a cautionary tale for the diagnosis of channelopathies, in which an unreported phenotypic presentation or mode of inheritance for the variant of interest can hinder the identification of causative variants and adequate treatment choice.