Genetic Testing of Non-familial Deaf Patients for CIB2 and GJB2 Mutations: Phenotype and Genetic Counselling

Abstract

CIB2 and GJB2 genes variants contribute significantly in familial cases of prelingual recessive hearing loss (HL). This study was aimed to determine the CIB2 and GJB2 variants and associated phenotype in 150 non-familial individuals with HL. After getting informed consent, 150 non-familial deaf patients were enrolled and blood samples were obtained for DNA extraction. Pure tone air conduction audiometry was performed. Coding exons of CIB2 and GJB2 genes were Sanger sequenced. A tetra primer ARMS assay was developed for recurrent CIB2 variant. Four bi-allelic GJB2 variants, c.71G>A p.(Trp24*), c.231G>A p.(Trp77*), c.235delC p.(Leu79Cysfs3*) and c.35delG p.(Gly11Leufs24*), were found in nine hearing impaired individuals. We also found four homozygotes and five carriers of c.380G>A p. (Arg127His) variant of controversial clinical significance. CIB2 sequencing revealed single recurrent variant c.272T>C p. (Phe91Ser) segregating with HL in ten individuals. Among our patients, c.71G>A (p.Trp24*) was the most common variant, accounted for 45% of GJB2 variants. Two known GJB2 variants, c.235delC p. (Leu79Cysfs3*) and c.310del14 p. (Lys105Argfs2*), are reported here for the first time in Pakistani population. Our data further support the benign nature of c.380G>A p. (Arg127His) variant. For CIB2, c.272T>C p. (Phe91Ser) is the second common cause of HL among our sporadic cases. Phenotypically, in our patients, individuals homozygous for GJB2 variants had profound HL, whereas CIB2 homozygotes had severe to profound prelingual HL. Our results suggest that GJB2 and CIB2 are common cause of HL in different Pakistani ethnicities.