Explaining racial disparity in systemic lupus erythematosus: Environmental and genetic risk factors in the carolina lupus study

PURPOSE: Systemic lupus erythematosus (SLE) is an autoimmune disease that disproportionately affects women and minorities. The incidence and prevalence of SLE are at least 3 times higher in African-Americans than in whites, but the reasons for this disparity are unclear. METHODS: Here we summarize the racial distribution of genetic and environmental risk factors for SLE in a population-based case-control study in the southeastern United States. Cases were SLE patients (n = 265; 90% female, diagnosed 1/95–7/99) in 60 contiguous counties of North Carolina and South Carolina. Controls (n = 355) were randomly selected from driverʹs license registries and frequency-matched to cases on age, sex, and state. More cases were African-American (60%), compared to controls (28%). Reproductive, hormonal, occupational, and medical histories were collected by in-person interview. Blood for DNA analyses was provided by 92% of cases and 85% of controls. RESULTS: Most of the statistically significant associations were observed in both African-Americans and whites, including hormonal or reproductive risk factors (i.e., not breastfeeding, pre-eclampsia), occupational exposures (i.e., silica, mercury), medication allergy, and herpes zoster, and differences by race were not statistically significant. Transfusions were uniquely associated with SLE in African-Americans, perhaps due to the low prevalence of transfusions among African-American controls. Various polymorphisms in immune system and metabolism genes showed modest associations with SLE, some in both races, some in African-Americans only and some in whites only. The frequency of most observed risk factors did not substantially differ in African-Americans compared with the frequency in whites. CONCLUSIONS: The increased risk of SLE in African-Americans did not appear to be explained by the strength of associations or prevalence of the risk factors we observed. Future analyses are planned to examine the role of personal and social stressors (e.g., racism and poverty) that could contribute to the racial disparity in risk of SLE.