RPGR and cone-rod dystrophy: The retinitis pigmentosa GTPase regulator (RPGR) is an alternatively spliced gene, producing both constitutive (RPGR1–19) and retinal specific (RPGRORF15) isoforms that function to regulate outer segment disc turnover, with pathogenic mutations causing a spectrum of retinal disease, from RP to cone-rod dystrophy to cone dystrophy7.