Retinitis Pigmentosa (RP) is a group of heterogeneous genetic disorders with a worldwide prevalence of 1 in 4000 individuals . RP can be inherited in autosomal, X-linked or mitochondrial format. X-linked RP (XLRP) is one of the most severe forms of retinopathies, accounting for about 10-20% of all RP cases. Mutations in the Retinitis Pigmentosa Gtpase Regulator (RPGR) gene are the major cause of XLRP, accounting for 70 to 80% of affected XLRP cases . The initially identified RPGR (RPGRex1-19) contains 19 exons and encodes for a predicted 90 KDa protein. A subsequent study identified a large C-terminal exon, called ORF15, in the major functional form (RPGRORF15). The exon ORF15 encodes a repetitive glycine and glutamic acid-rich domain with a evolutionary conserved basic C-terminal domain, and harbors a high frequency of reading-frameshift and premature stop mutations, producing truncated proteins of varying length. More than 300 RPGR mutations have been reported, most causing XLRP, a few causing human cone-rod, cone, or macular dystrophies, or syndromal forms of XLRP with primary ciliary dyskinesia and hearing loss.
RPGR is predominantly expressed in connecting cilia of photoreceptors, but expression has been reported in photoreceptor outer segments in some species. In mammalian and non-mammalian cell lines, RPGR localizes in centrosome of non-ciliated cells, and in basal body of ciliated cells. Knock-down of RPGR in human retinal pigmented epithelium hTERT-RPE1 cell line caused defects in cilia genesis, suggesting RPGR has a role in the initial steps of cilia formation and/or stability
(Xinhua Shu: Gene Therapy for X-Linked Retinitis Pigmentosa)
Last date updated on June, 2014