Around 25% of all RP cases are caused by mutations in the rhodopsin gene (RHO) (Hartong et al., 2006), with a proline to histidine change at codon 23 (P23H) in RHO being the first RP mutation identified in human patients (Dryja et al., 1990a; Dryja et al., 1990b). The gene discussed is RHO; the disease is retinitis pigmentosa 1.