CHM and Usher syndrome: In Usher syndrome (Liu et al., 1998; Liu et al., 1999) and X-linked choroideremia (MacDonald et al., 1998; Seabra, 1996), which also involve defects in melanosome movement into the apical processes due to loss of function of myosin VIIa and Rep1, respectively, the photoreceptors also gradually degenerate.