<i>KCNH1</i> variants associated with neurodevelopmental disorders exhibit prominent gain-of-function

Pathogenic variants in KCNH1 , encoding the human ether-á-go-go voltage-gated potassium channel (EAG1, K V 10.1), are associated with the neurodevelopmental disorders Temple-Baraitser syndrome (TBS), Zimmermann-Laband syndrome (ZLS), and epileptic encephalopathy. Investigating the functional consequences of KCNH1 variants can provide information about molecular and cellular pathophysiological mechanisms, and help guide therapeutic directions. In this study, we determined the functional properties of 26 disease-associated KCNH1 variants including three recurrent and five that were previously unpublished. Findings were compared to the wildtype (WT) channel along with six rare population variants. Our approach used automated patch clamp recording of heterologously expressed KCNH1 variants in both the homozygous state (variant alone) and the clinically-relevant heterozygous state (variant co-expressed with WT channels). We also examined the impact of alternative splice isoforms on functional consequences of specific variants. We demonstrated that the majority of disease-associated KCNH1 variants exhibit features consistent with gain-of-function including hyperpolarized voltage-dependence of activation, accelerated activation kinetics, or both that promote hyperpolarization of the resting membrane potential. By contrast, one unique variant discovered previously in an autism cohort had a depolarized voltage-dependence of activation and was associated with a depolarized resting potential in cells. Pharmacological testing of KCNH1 variants demonstrated differences in potency for channel block by imipramine and an investigational non-selective potassium channel blocker (LY97241) for specific variants. Collectively, our findings support gain-of-function as the most common, albeit not exclusive, molecular mechanism underlying KCNH1 -related disorders and suggest opportunities for potential therapeutic drug repurposing strategies for these conditions.