Functional Screening of Kv7.5 Channel Variants Associated with Neuronal Dysfunction

The KCNQ5 gene encodes Kv7.5 channels, which contribute to the regulation of neuronal excitability. Kv7.5 genetic variants associated with neurological dysfunction have been reported, but functional characterization of Kv7.5 variants is limited and causal links to pathogenicity are lacking. We have conducted the first automated patch clamp functional screen of a panel of heterozygous Kv7.5/Kv7.3 channel variants. We tested nine mutations located in diverse locations throughout the Kv7.5 channel and identified some variants with gain-of-function effects (L341I+/-, G347S+/-, P369R+/-, R497C+/-), some with loss-of-function effects (V145G+/-, W303C+/-), and others with no apparent effect (A131V+/-, R359H+/-, R491H+/-). Variants produced a gain of function by left-shifting the voltage-dependence of channel activation alone or in combination with increasing current density. Loss of function occurred as a result of reduced current density. Using these findings, we initiated the first z-score classification to guide understanding of Kv7.5 variant pathogenicity, which can be refined as more variants are functionally characterized and new variants are discovered. Lastly, we observed higher sensitivity to channel block by XE991 in L341I+/-, G347S+/-, P369R+/- gain-of-function variants indicating potential for targeted pharmacogenetic approaches to restore normal Kv7.5 channel function.