RPGR and Retinal dystrophy: Following the exclusion of coding variants in X-linked genes known to cause retinal dystrophy (RPGR and RP2), the IRDF-1 locus was mapped by haplotype analysis to a 3.5 Mb region on Xq26.3–27.2 between markers DXS1062 and DXS1227 (Figures 1 and S2).