S1PR2 and Profound hearing impairment: Only 3 of these have been identified in humans; ADGRV1, which is an Usher syndrome type II gene (Weston et al. 2004), DMD, which has been associated with congenital hearing impairment as well as muscular dystrophy (Pfister et al. 1998), and S1PR2, mutations in which lead to congenital profound hearing impairment (Santos-Cortez et al. 2016), although a point mutation in S1pr2 in mice results in early-onset progressive hearing loss (Ingham et al. 2016).