GJB2 and autosomal recessive nonsyndromic hearing loss 1A: Despite the extraordinary genetic heterogeneity of nonsyndromic HL, homozygous or compound heterozygous mutations in the GJB2 gene (gap junction protein, β-2, OMIM 121011, 13q12.11) encoding transmembrane protein connexin 26 (Cx26) are the most common cause of nonsyndromic autosomal recessive deafness 1A (DFNB1A, OMIM 220290) in many populations [4].