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.