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. The gene discussed is SMPX; the disease is hearing loss disorder.