ABCA4 and retinitis pigmentosa 1: However, as Case 5a illustrates, this is not always present, and, in fact, peripapillary sparing has been reported to be absent in about 2 to 7% of cases [25]; (4) pigment in ABCA4-RD is typically more prevalent in larger round clumps, whereas, in RP, it is usually more elongated and bony spicule-like; (5) if the pedigree suggests an inheritance pattern other than AR, this points away from ABCA4-RD, though one should always keep in mind the possibility of pseudo-dominant inheritance.