The United States to Africa lupus prevalence gradient revisited

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that has a significantly higher prevalence, morbidity and mortality in African Americans compared with Americans of European descent. The pathogenesis of lupus is unclear but appears to be a result of environmental factors interacting with a genetically susceptible host. Despite the high disease load of SLE in African Americans, there is the perception that lupus is relatively rare in Africa. This prevalence gradient suggests that comparative studies of related cohorts from the two continents may provide insight into the genetic/environmental interactions that result in the development of lupus. To define if a lupus gradient exists, we began a study of autoimmunity prevalence utilizing two unique cohorts. The first is the Gullah population of the Sea Islands of South Carolina, who are unique in their low genetic admixture and their known ancestral heritage. The second is the population of young women served by the West Africa Fistula Foundation in Bo, Sierra Leone. Anthropologic studies indicate a direct ancestral link between the Gullah population and Sierra Leoneans. Since it is impossible to perform an epidemiologic study of lupus in Sierra Leone at this time, we assessed the prevalence of lupus serum autoantibodies, serologic evidence of specific infections and levels of serum 25-OH vitamin D in young women in the two cohorts who have no known relatives with lupus. Our results indicate similar prevalence of serum antinuclear antibodies in the two cohorts, though there was a significantly increased prevalence of antiphospholipid and anti-Sm antibodies in the Sierra Leone cohort. Seropositivity to common viral infections was significantly higher in women from Sierra Leone, while serum 25-OH vitamin D levels were markedly lower in the Gullah population. These data suggest that the prevalence of autoimmunity is similar in the two populations, but that there are significant environmental differences that may impact progression to autoimmune disease. Further studies comparing these two cohorts is likely to provide important insight into the impact of environmental factors on development of lupus.