Background: Many of the voltage-gated potassium channels (KV1–KV12) are expressed in the central nervous system (CNS), and play important roles in neuronal excitability and neurotransmitter release. KCNA2 gene encodes an α-subunit of the Kv1.2 channel, and dysfunction of this gene causes epileptic encephalopathy. We herein report a case of epileptic encephalopathy caused by KCNA2 mutation that is characterized by intractable epilepsy, and severe mental retardation, and various involuntary movements.

Case Report: Patient is a 12-year-old boy who had been seen at our hospital soon after birth because of erratic myoclonus without EEG changes. After that, he developed severe psychomotor retardation and various involuntary movements such as dystonia, chorea, ballismus and abnormal ocular movement. He has been suffering from intractable epilepsy since thirteen months of age. Also, he developed pyramidal signs and disturbance of sleep cycle. His blood examinations showed no abnormality. A sequence of his brain magnetic resonance imaging showed progression of diffuse brain atrophy, including basal ganglia, cerebellum, and brainstem. We identified a novel de novo heterozygous missense mutation in the KCNA2 gene, c.1121C＞G(p.Thr374Ser) by whole exome sequencing.

Discussion: The present case is characterized by neonatal onset of various involuntary movements and neurodevelopmental delay, diffuse brain atrophy involving basal ganglia, cerebellum and brainstem, and disturbance of sleep cycle that implies autonomic nervous system dysfunction. These findings expand a phenotypic spectrum of epileptic encephalopathy caused by KCNA2 mutation.