Mutations in the RPGR gene are the major cause of RP, accounting for more than 70% of XLRP and over 20% of nonsyndromic RP in North American families [24, 25]. RPGR mutations are responsible for 8.8% of Japanese RP patients [26] and 4.26% of Chinese patients with cone-rod dystrophy [27]. This evidence concerns the gene RPGR and cone-rod dystrophy.