Kv4.2 V404M Mutation Induces Epileptiform Activity and Multiple Behavioral Abnormalities in Heterozygous Knock-in Mice

The KCND2 gene encodes the Kv4.2 voltage-gated potassium channel alpha subunit that underlies the somatodendritic subthreshold A-type current (I SA ) important for membrane excitability and dendritic signal integration and processing. A heterozygous missense mutation in KCND2 (NM_012281.2: c.1210G>A) was identified in patients with early-onset epilepsy, autism, and global developmental delay, producing a conservative replacement of valine 404 to methionine (Lee et al., 2014; Zhang et al., 2021). To investigate the potential pathological role of the Kv4.2 V404M mutation, we generated Kv4.2 (V404M/+) heterozygous knock-in C57BL/6J mice using CRISPR technology and compared features of development, physiology, and behavior of Kv4.2 (V404M/+) mice to age- and sex-matched wild-type (Kv4.2 (+/+) ) littermate controls. Kv4.2 (V404M/+) mice exhibit significant mortality during early development (>50%), poor reproductive behavior, decreased body weight of males (25-30%), altered I SA functional properties, and 4-5 Hz spike-wave epileptiform discharges. These discharges occur frequently during periods of inactivity, with over 80% occurring during NREM sleep. ΔFosB was found to be significantly elevated in the cortex and hippocampus of Kv4.2 (V404M/+) mice. A combination of home-cage measurements and behavioral assays reveal that Kv4.2 (V404M/+) mice exhibit significant alterations in exploratory behavior, social interaction, fear conditioning, and spatial memory. Our results indicate that the Kv4.2 V404M mutation is sufficient to produce a dominant spectrum of physiological and behavioral changes in mice that likely have important implications for understanding the etiology and potential therapeutic approaches for this human channelopathy. Significance statement A V404M point mutation in Kv4.2 has been identified in multiple human patients with autism spectrum disorder and/or global developmental delay with epilepsy. Here, we show in a mouse knock-in model that the heterozygous Kv4.2 (V404M/+) mutation is sufficient to produce a syndrome of epilepsy and aberrant behavioral phenotypes. Based on these results, it is also very likely that many other Kv4.2 subunit mutations found in similar patients are also disease-causing. Our Kv4.2 (V404M/+) mouse model also provides an important new tool to understand how dysfunction of Kv4.2 can lead to neuropathology and to validate targeted therapeutic approaches to treating this disorder.