GJB2 and hereditary disease: On the other hand, mutations in the skin-expressed connexin genes GJB2 (connexin 26), GJB3, GJB4 (connexin 31 and 30.3), GJB6 (connexin 30), and Gap Junction Alpha 1 (connexin 43) have been linked to human hereditary diseases affecting both the epidermis and cochlea [7].