Abstract
<jats:p> G protein-gated inwardly rectifying potassium (GIRK2) channels regulate neuronal excitability and are implicated in neurodevelopmental disorders. A rare KCNJ6 variant, G154C (hGIRK2 <jats:sub>G154C</jats:sub> ), was identified in a patient with mild Keppen-Lubinsky syndrome features, contrasting with severe phenotypes linked to other selectivity filter mutations. Here we combined molecular dynamics simulations and patch-clamp electrophysiology to characterize the hGIRK2 <jats:sub>G154C</jats:sub> mutant, revealing a widened selectivity filter that resulted in loss of potassium selectivity, aberrant sodium permeation, and loss of inward rectification, indicating a severe gain-of-function phenotype. An in silico and electrophysiological drug screen identified FDA-approved compounds, including nefazodone and eletriptan, that potently inhibited GIRK2 and GIRK2 <jats:sub>G154C</jats:sub> through distinct blocking mechanisms. These findings elucidate the structural and functional impact of the G154C mutation and highlight potential pharmacological tools and therapeutic candidates for the treatment of GIRK2 channelopathies. </jats:p>