X-linked retinitis pigmentosa (XLRP) is a retinal degeneration disorder. The most common form of XLRP has been localized to the gene locus RP3 by linkage and deletion analysis. RP3 maps to chromosome Xp21.1 between CYBB and OTC. The sushi-repeat-containing protein, x chromosome (SRPX) gene, also designated ETX1, resides within this region and is deleted in XLRP patients. There are at least two splice variants of SRPX, one of which contains a thirty amino acid signal peptide. Both variants contain three complement control protein domains, a hydrophobic region for membrane anchorage, and a cytoplasmic carboxy terminus. SRPX is expressed in retina and heart. SRPX is highly homologous to the drs (downregulated by v-src) human homolog, which suggests a role for SRPX as a tumor suppressor.
