Abstracts

Rationale: Pathogenic variants in KCNB1 are responsible for epileptic encephalopathy (EE). To gain insight into the mechanisms underlying KCNB1 encephalopathy by examining the electrophysiologic properties and expression efficiency of mutant Kv2.1 channels. Methods: Detailed clinical data were collected from two EE patients with KCNB1 variants in China. Whole-cell patch clamp was performed to record the electrophysiological activity of Kv2.1 channels. Protein expression of wild KCNB1 and mutant KCNB1 was detected Western blotting. Results: We identified two novel KCNB1 variant (G379V, P408S) by whole exome sequencing of patients which both started with psychomotor developmental delay at infancy stage, then presented with intractable epilepsy. Their EEG results showed continuous or multiple discharges, brain MRI scans didn’t show abnormality. The two mutants both fall in the conserved domain of Kv2.1, voltage clamp analysis showed no detectable potassium current in a heterologous expression system expressing the KCNB1- G379V/ KCNB1- P408S variant. Furthermore, western blotting demonstrated apparent reduction in the amount of KCNB1- G379V and KCNB1-P408S at the level of total protein and cell surface compared to wildtype. Conclusions: De novo loss-of-function KCNB1 mutations are involved in EE which has its own clinical features including proceeding with intellectual disabilities before intractable epilepsy. Other than decreased channel functional properties reported before, the reduced protein expression or deficient trafficking to the plasma membrane is the possible pathogenesis of KCNB1 related EE which is firstly disclosed in the study. Funding: This work was supported by the National Key Research and Development Program of China (Grant Nos. 2016YFC1306202 and 2016YFC0904400) and the National Natural Science Foundation of China (Grant Nos. 81771409, 81771408, 81701541, and 81671297).