Epilepsy and neurobehavioral abnormalities in mice with a KCNB1 pathogenic variant that alters conducting and non-conducting functions of K V 2.1

Developmental and epileptic encephalopathies (DEE) are a group of severe epilepsies that usually present with intractable seizures, developmental delay and are at a higher risk for premature mortality. Numerous genes have been identified as a monogenic cause of DEE, including . The voltage-gated potassium channel K2.1, encoded by , is primarily responsible for delayed rectifier potassium currents that are important regulators of excitability in electrically excitable cells, including neurons and cardiomyocytes. The pathogenic variant -p.G379R was identified in an infant with epileptic spasms, atonic, focal and tonic-clonic seizures that were refractory to treatment with standard antiepileptic drugs. Previous work demonstrated deficits in potassium conductance, but did not assess non-conducting functions. To determine if the G379R variant affected clustering at endoplasmic reticulum-plasma membrane junctions K2.1-G379R was expressed in HEK293T cells. K2.1-G379R expression did not induce formation of endoplasmic reticulum-plasma membrane junctions, and co-expression of K2.1-G379R with K2.1-WT lowered induction of these structures relative to K2.1-WT alone, suggesting a dominant negative effect. To model this variant , we introduced into mice using CRISPR/Cas9 genome editing. We characterized neurological and neurobehavioral phenotypes of () and () mice, and screened for cardiac abnormalities. Immunohistochemistry studies on brains from (WT) and mice revealed genotype-dependent differences in the levels and subcellular localization of K2.1, with reduced plasma membrane expression of the K2.1-G379R protein, consistent with data. and mice displayed profound hyperactivity, repetitive behaviors, impulsivity and reduced anxiety. In addition, both and mice exhibited abnormal interictal EEG abnormalities, including isolated spike and slow waves. Spontaneous seizure events were observed in mice during exposure to novel environments and/or handling, while both and mutants were more susceptible to induced seizures. and mice exhibited prolonged rate-corrected QT interval on surface ECG recording. Overall, the mice recapitulate many features observed in individuals with DEE due to pathogenic variants in . This new mouse model of associated DEE will be valuable for improving the understanding of the underlying pathophysiology and will provide a valuable tool for the development of therapies to treat this pharmacoresistant DEE.