ABCA4 and retinitis pigmentosa: Variants in the ABCA4 gene are responsible for STGD1 (Allikmets, 1997), retinitis pigmentosa (RP) (Cremers et al., 1998; Rozet et al., 1999), cone–rod dystrophy (CRD) (Cremers et al., 1998; Maugeri et al., 2000), and retinal dystrophy (Singh et al., 2006).