PTPRQ and deafness: The analyses of mouse deafness mutations have identified several proteins involved in the regulation of hair cell stereocilia length, including espin [30], [31], myosin XVa [32], whirlin [33], [34], [35], and EPS8 [36], [37], whose absence results in shortened stereocilia, and myosin VIIa [38], myosin VI [39], [40] and PTPRQ [41], [42] whose absence results in elongated stereocilia.