GJB2 and Hearing impairment: In addition, 4 subjects with noise-induced hearing impairment had an explicit noise exposure history and classic noise-induced hearing loss audiograms indicating that the hearing threshold at 4 kHz was affected, and had no GJB2 mutations; one patient (IV:22) showed much more severe hearing loss and compound heterozygosity for GJB2 (c.524C > A/235delC).