The incidence of systemic lupus erythematosus in North American Indians.

The annual incidence (AI) of systemic lupus erythematosus (SLE) was determined in 75 highly inbred North American Indian tribes, a total of approximately 800,000 people, during the fiscal years 1971-1975. Seventy-two of the Indian tribes had an AI of SLE which was of similar magnitude to previously published studies from Sweden, Rochester (Minn.), Alabama, New York City, and San Francisco. However, Three tribes, the Crow, Arapahoe, and Sioux Indians, had a markedly elevated AI of SLE. These three tribes share common historical, geographic, and cultural characteristics. Further, they all reside in the northern half of the United States, in states that do not receive intense sun exposure, thereby eliminating photosensitivity as a major determinant of this increased prevalence. Finally, the AI of SLE in the Sioux Indians was highest for "full-blooded" members and lowest for genetic admixtures.