Another hiPSC line has been created by Dykxhoorn and co-workers from a patient with a mutation in the Small Muscle Protein X-linked (SMPX) gene that may serve as a model of X-linked deafness 4 (DFNX4) [92]; increased susceptibility to loud noise and progressive HL have been observed in Smpx KO mice, associated with progressive degeneration of stereocilia in the OHC bundles [99]. The gene discussed is SMPX; the disease is hearing loss, X-linked 4.