Abstract
The aim of the study was to determine (1) the frequency and type of mutations in the coding region of the GJB2 gene (sequencing), (2) the frequency of splice site mutation IVS1 + 1G > A in the GJB2 gene (multiplex ligation-dependent probe amplification analysis), (3) possible copy number changes in the GJB2, GJB3, GJB6, and WFS1 genes (multiplex ligation-dependent probe amplification analysis), and (4) the frequency of del(GJB6-D13S1830) in the GJB6 gene in 58 unrelated patients with nonsyndromic hearing loss from Croatia. About 44.8% of our patients presented with mutation in the GJB2 gene. We identified seven sequence variations. Six of them had previously been reported as disease related (35delG, W24X, V37I, L90P, 313del14, and IVS1 + 1G > A), and we report here for the first time one novel variant, −24A > C. We detected the greatest frequency of 35delG allele compared to the other alleles (35.3%). Allelic frequencies of other common mutations accounted for 2.6-0.9% of analyzed chromosomes. Neither GJB6 deletion nor copy number changes in the GJB2, GJB3, GJB6, and WFS1 genes were found. The 35delG/35delG genotype was associated with severe to profound hearing loss in 94% of 35delG homozygotes. High mutation rate (44%) indicates that testing of the GJB2 gene will clarify the genetic cause in almost half of the cases of recessive nonsyndromic hearing loss in Croatia.