ABCA4 and retinitis pigmentosa: Furthermore, although biallelic mutations in ABCA4 are found in most patients with autosomal recessive STGD, there are studies which have shown that mutations in the ABCA4 gene are responsible for a wide variety of other retinal dystrophy phenotypes, such as cone-rod dystrophy (CRD), and retinitis pigmentosa (RP) [5], [6].