A novel variant c.1185_1196dup (p.(Gly396_Ser399dup)) in the SLC26A4 gene associated with recessive hearing loss

Pathogenic variants in the SLC26A4 gene (solute carrier family 26, member 4) are a common cause of inherited hearing loss. The SLC26A4 gene encodes the transmembrane protein pendrin, a member of the SLC26 anion transporter family, with predominant expression in the inner ear, thyroid, and kidney tissues. Pathogenic SLC26A4 variants cause nonsyndromic recessive hearing loss (DFNB4) and Pendred syndrome (sensorineural hearing loss and thyroid dysfunction). In many studies analyzing the SLC26A4 gene, along with patients who have two recessive pathogenic SLC26A4 variants (M2 patients) and an accurate molecular genetic diagnosis can be made, a group of patients with only one pathogenic SLC26A4 variant (M1 patients) is often identified, which creates a diagnostic problem. The presence of M1 patients may reflect copy number variations (CNVs, deletions/duplications) in the SLC26A4 gene that are not detected by routine diagnostic methods. The aim of the study is to search for deletions/duplications in the SLC26A4 gene using the MLPA (Multiplex Ligation-dependent Probe Amplification) method in thirteen patients belonging to the indigenous people of the Tyva Republic (Southern Siberia), in whom only one pathogenic SLC26A4 variant (M1 patients) was identified during the study of the etiology of hereditary hearing loss. As a result of MLPA analysis and molecular cloning in DNA samples of three M1 patients from two related Tuvinian families, a novel variant was revealed – tandem duplication of twelve nucleotides (c.1185_1196dup) in exon 10 of the SLC26A4 gene. This variant is an in-frame insertion resulting in the inclusion of four additional amino acid residues Gly-Phe-Phe-Ser (p.(Gly396_Ser399dup)) in a highly conserved region of the pendrin protein. Most predictive programs predict the damaging effect of the c.1185_1196dup variant on the structure and function of the pendrin protein. The pathogenicity of the c.1185_1196dup variant is supported by its segregation with hearing pathology in the pedigree of patients in whom it was found in a compound heterozygous state with pathogenic SLC26A4 variants, as well as its absence in a control sample of Tuvinians and in the world genomic databases. Functional in vitro studies are needed to confirm the potentially deleterious effects of the novel c.1185_1196dup (p.(Gly396_Ser399dup)) variant and its association with hearing pathology. 

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