For example, mutations in CRX cause both early-onset Leber congenital amaurosis (LCA) and progressive CRD or RP, where disease progresses over time (Freund et al., 1997; Rivolta et al., 2001; Sohocki et al., 1998; Swaroop et al., 1999). Here, CRX is linked to Leber congenital amaurosis.