Pathogenic Mechanism of the KCNQ4 Gene Variant in Hearing Loss and Functional Validation in a Zebrafish Model

The KCNQ4 gene is closely associated with autosomal dominant nonsyndromic hearing loss (DFNA2) and encodes a potassium channel crucial for potassium ion circulation in the inner ear. This study identified a novel KCNQ4 variant, c.825G>T (p.Trp275Cys), associated with progressive hereditary hearing loss in a family. In vitro experiments and structural predictions revealed that this mutation did not affect KCNQ4 channel localization, subunit assembly, or pore size. However, the mutation induced longitudinal extension of the channel, reduced protein stability, and impaired potassium ion selectivity, thereby disrupting potassium ion homeostasis in the inner ear and ultimately leading to hearing loss. Zebrafish models further validated the critical role of the kcnq4 gene in inner ear development. We used morpholino to knock down kcnq4 in zebrafish and rescued the phenotype by reintroducing wild-type kcnq4 mRNA. This approach revealed significant changes in otolith morphology, a marked reduction in hair cell numbers, and abnormal motor responses. Additionally, we cloned and completed the coding sequence (CDS) of kcnq4 mRNA from the AB strain of zebrafish, enriching the available database information. Our findings provide new insights into the molecular mechanisms underlying KCNQ4-related hereditary hearing loss and lay the groundwork for developing precision treatments and early intervention strategies.