RPGR and retinitis pigmentosa 1: Previous studies have shown that patients with X-linked RP due to mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene have faster rates of change for VA than patients with dominant RP due to mutations in the rhodopsin (RHO) gene or than patients with autosomal recessive USH2A gene (Usher syndrome type II) [77].