S1PR2 and Hearing impairment: Only 3 of these have been identified in humans; ADGRV1, which is an Usher syndrome type II gene [22], DMD, which has been associated with congenital hearing impairment as well as muscular dystrophy [23], and S1PR2, variants in which lead to congenital profound hearing impairment [24], although a point variant in S1pr2 in mice results in early-onset progressive hearing loss [25].