Gene therapy for x-linked retinitis pigmentosa

Retinitis Pigmentosa (RP) is a group of heterogeneous genetic disorders with a worldwide prevalence of 1 in 4000 individuals [1]. 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 [2]. The initially identified RPGR (RPGRex1-19) contains 19 exons and encodes for a predicted 90 KDa protein [3]. 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 [4]. 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 [5].