Hearing loss features in GJB2 biallelic mutations and GJB2/GJB6 digenic inheritance in a large Italian cohort

The aim of this study was to describe the clinical features of hearing loss due to mutations on connexin 26/30 coding genes (GJB2/GJB6). Mutations in the GJB2 gene are found to account for approximately 50\% of cases of autosomal recessive non-syndromic deafness. Several European studies have estimated that the GJB2 healthy carrier condition involves about 2-4\% of the population, with the 35delG mutations being the most common. A 342-kb deletion truncating the GJB6 gene (encoding connexin-30) has been associated with autosomal recessive non-syndromic deafness, mostly as digenic inheritance of the Cx30 deletion/Cx26 mutation. The following retrospective study describes audiological features and genotypes of a large cohort of 376 Italian hearing-impaired patients who underwent genetic screening for the GJB2/GJB6 genes and received follow-up care at our centre between January 2002 and October 2006. Sixteen different genotypes causing deafness in more than 27\% of patients with either biallelic mutations or digenic inheritance GJB2/GJB6 were identified. The most frequent mutations were 35delG, M34T, L90P, and R184P.