Occurrence of del(GIB6-D13S1830) mutation in Italian non-syndromic hearing loss patients carrying a single GJB2 mutated allele.

Molecular screening for GJB2 (connexin 26) mutations represents the standard diagnostic approach for the genotype definition of non-syndromic deafness. Nevertheless, a single GJB2 pathogenic mutation is detectable in a relevant number of cases, therefore failing to explain the phenotype. We aimed at assessing the occurrence of the recently described del(GIB6-D13S1830) mutation, occurring in the connexin 30 gene, in a group of Italian hearing-impaired patients carrying a single GJB2 mutated allele. A total of 59 non-syndromic hearing loss (NSHL) patients were screened for GJB2 mutations. Among these, nine NSHL patients were found to be heterozygous for a single GJB2 mutation. These patients, heterozygotes for different GJB2 mutated alleles (35delG, L90P, M34T, V153I), together with 11 additional 35delG/neg cases previously described, were studied for the presence of the del(GIB6-D13S1830) mutation. Two double heterozygotes del(GIB6-D13S1830)/35delG were identified. In both cases the degree of hearing loss was profound. Furthermore, GJB2 molecular screening led to the identification of a novel change (T55G) occurring in compound heterozygosity with the V37I mutation. In conclusion, our data suggest a significant frequency of del(GIB6-D13S1830) mutation in Italian hearing-impaired subjects (10% of unexplained GJB2 heterozygotes) similar to that reported in other European countries.