Authors:

Alexander D. Crowell

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Genetic variants in neuronal potassium channel genes are associated with epilepsy and neurodevelopmental disorders. Variants in KCNH1, which encodes the voltage-gated potassium channel K,10.1, cause two closely related neurodevelopmental disorders: Temple-Baraitser syndrome (TBS) and Zimmerman-Laband Syndrome (ZLS). These disorders affect young children with epilepsy, developmental delay, intellectual disability, and other non-neuronal features. Despite this clinical association, the mechanisms by which disease-causing variants alter channel function remain poorly understood. We investigated the functional effects of R357Q, the most recurrent pathogenic KCNH1 variant. Human embryonic kidney (HEK293) cells were transiently transfected with R357Q or wild-type KCNH1 plasmids, and potassium currents were measured using whole-cell voltage clamp electrophysiology. This technique allows precise control of membrane potential while recording ion channel activity. Cells expressing the R357Q variant exhibited markedly faster channel opening (activation kinetics) and a leftward shift in voltage dependence compared with cells expressing wildtype (WT) channels. These findings indicate that the variant channel activates at more negative voltages and therefore opens more readily than the WT channel. We also investigate the hypothesis that strong pre-pulse hyperpolarization preceding channel activation slows channel kinetics in R357Q. We examined this effect using two alternatively spliced KCNH1 isoforms (isoform 1, isoform 2). Hyperpolarized pre-pulses significantly slowed activation of the R357Q variant in both channel isoforms. In WT KCNH1, the effect differed between isoforms; isoform 2 exhibited greater slowing of activation following hyperpolarized pre-pulses compared to isoform 1. Notably, isoform 2 contains a short deletion in the extracellular S3—S4 linker region, suggesting that structural differences in this region may influence voltage-dependent gating behavior. These findings suggest that altered voltage sensitivity and gating behavior contribute to channel dysfunction in TBS and ZLS. Understanding how specific mutations disrupt potassium channel function provides mechanistic insight into epilepsy pathogenesis and may inform future therapeutic strategies targeting channel gating dynamics.

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Northwestern University

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Co-authors:

Alexander D. Crowell