Double heterozygous mice for both Gjb2 and Gjb6 mutations (Gjb2+/− Gjb6+/− double heterozygotes) exhibit a moderate hearing impairment and reduced endocochlear potential compared with single heterozygotes [84], in contrast with the phenotype observed in humans, wherein most double heterozygotes for del(GJB6-D13S1830) and a GJB2 mutation have severe or profound hearing impairment [82,83,85-89]. The gene discussed is GJB2; the disease is hearing loss disorder.