OFD1 and retinitis pigmentosa 23: Mutations within OFD1 are also responsible for 4 recessive X-linked phenotypes including mental retardation with macrocephaly, Simpson-Golabi-Behmel syndrome type 2, Joubert Syndrome type 10, and Retinitis Pigmentosa 23 [5]. OFD1 gene escapes X-inactivation, which means that it is expressed from both X chromosomes in females (while most genes are expressed from only one X chromosome) [6].