Efficient Molecular Genetic Diagnosis of Enlarged Vestibular Aqueducts in East Asians

Abstract

Context: Enlargement of the vestibular aqueduct (EVA) is a commonly detected inner ear anomaly related to hearing loss and often associated with mutations of SLC26A4 encoding pendrin, a transmembrane exchanger of Cl⁻, I⁻, and HCO₃⁻. Here we describe the phenotypes of 27 Korean EVA subjects and their SLC26A4 genotypes determined by bidirectional nucleotide sequencing. Results: The detected variants include two novel missense substitutions (p.V138L and p.P542R). We characterized the ability of p.V138L and p.P542R pendrin products to traffic to the plasma membrane in COS-7 cells and to transport Cl⁻, I⁻, and HCO₃⁻ in Xenopus oocytes. The results indicate that p.P542R is a benign polymorphic variant, whereas p.V138L is a pathogenic mutation. Since this and other studies of East Asian EVA cohorts show that the majority of SLC26A4 mutations affect either or both of two amplicons (exons 7-8 and 19), we developed a hierarchical protocol that integrates direct sequencing with denaturing high-performance liquid chromatography analyses for detection of SLC26A4 mutations in these populations. We validated the cost efficiency of the integrated protocol by a simulated screen of published East Asian EVA cohorts with known SLC26A4 genotypes. Conclusions: Our study further defines the spectrum of SLC26A4 mutations among East Asians and demonstrates a rapid and efficient protocol for their detection.