For example, partial or complete loss of ABCA4 functions cause many blinding diseases in humans including retinitis pigmentosa, cone-rod dystrophy and Stargdardt macular dystrophy, but ABCA4 KO in mice does not cause blindness unless combined with a deletion of other genes such as RDH8 [39]–[41]. Here, RDH8 is linked to retinitis pigmentosa.