GJB2 and Hearing impairment: Many studies aimed to highlight the specific roles of each domain of Cx26 protein reviewing the pathogenic effects of different mutations associated with nonsyndromic or syndromic hearing impairments in GJB2 gene and, as the different members of the connexin protein family are very similar in their topological organization, in other connexin genes [4,17,28,44,71,72,73,74,75,76,77].