POU3F4 and hearing loss disorder: To date, according to the Hereditary Hearing Loss website (http://hereditaryhearingloss.org), six loci (DFNX1–6) and five causative genes have been identified in X-linked hearing loss: PRPS1 (OMIM 311850) for DFNX1, POU3F4 (OMIM 300039) for DFNX2, SMPX (OMIM 300226) for DFNX4, AIFM1 (OMIM 300169) for DFNX5, and COL4L6 (OMIM 303631) for DFNX6.