Novel KCNB1 mutation associated with non-syndromic intellectual disability.

Potassium voltage-gated channel subfamily B member 1 (KCNB1) encodes Kv2.1 potassium channel of crucial role in hippocampal neuron excitation homeostasis. KCNB1 mutations are known to cause early-onset infantile epilepsy. To date, 10 KCNB1 mutations have been described in 11 patients. Using whole-exome sequencing, we identified a novel de novo missense (c.1132G>C, p.V378L) KCNB1 mutation in a patient with global developmental delay, intellectual disability, severe speech impairment, but no episode of epilepsy until the lastly examined age of 6 years old. Furthermore, she showed neuropsychiatric symptoms including hyperactivity with irritability, heteroaggressiveness, psychomotor instability and agitation. Our observation might expand the phenotypic spectrum of KCNB1-related phenotypes and raises the issue of the occurrence of the epileptic phenotype.