Audiological Phenotype of patients showing connexin 26/30 related deafness in a cohort including 628 patients.

Mutations in the GJB2 gene are found to account for approximately 50% of cases of autosomal recessive non-syndromic deafness. A 342-kb deletion truncating the GJB6 gene 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 628 hearing impaired patients who underwent genetic screening for the GJB2/GJB6 genes and received follow-up care at our centre between January 2002 and July 2008. Mutations in GJB2/GJB6 genes were found in over than 30% of cases. Twenty-seven different genotypes causing deafness in more than 25% of patients with either biallelic mutations or digenic inheritance GJB2/GJB6 were identified. The most frequent mutations of the GJB2 were 35delG, L90P, M34T, delE120 and R184P. The 342-kb deletion del(GJB6-D13S1830) was also quite frequent. In more than 14% of cases the cause of deafness was the homozygosis for the most common mutation among European people the 35delG. Although more than 70% of patients with biallelic/digenic inheritance of the Cx30 deletion/Cx26 mutation exhibit a severe to profound hearing loss, mild and moderate impairment were also found. Other clinical data such as course and degree of bilateral involvement were analysed too.