The prevalence of typical RP is estimated at approximately 1 in 3,000 to 1 in 5,000 individuals. RP affects about 1.5 million people worldwide and is the most common inherited retinal degenerations. The highest reported prevalence for RP, 1 in 1878, is among the Navajo Indians (Native American tribe of Northern America). A lifetime risk of developing RP in Denmark has been reported to be 1 in 2500. In Switzerland, the prevalence of RP has been reported to be as low as 1 in 7000. Sexual predilection has not been identified. However, as the expressivity of the X-linked RP is more severe in males, men may be affected slightly more than women. Ethnic preponderance has not been documented, but RP caused by mutations in particular genes may be more frequent in certain isolated or consanguineous populations.