Epidemiology, demographics, and genetics of sarcoidosis.

Epidemiological knowledge of sarcoidosis is based mainly on studies performed more than 30 years ago. These early case-control studies produced some interesting risk factor-disease associations, but a clear causative mechanism in sarcoidosis remains unknown. Studies in military and veteran populations showed a clear preponderance of sarcoidosis in African Americans compared with Caucasians. Our recent sarcoidosis incidence study in a racially heterogeneous population found African Americans at three- to fourfold greater risk, which was less than the 10 to 17 times greater risk previously reported. Females are consistently found at greater risk than males, although the relative risk difference generally does not exceed two. The striking racial differences and numerous reports of familial clustering suggest genetic susceptibility. We have found that familial sarcoidosis is almost three times more common in African-American (17%) than Caucasian cases (6%). Future genetic studies can benefit from the extensive catalog of candidate genes that is emerging from the human genome project. The epidemiological evidence to date strongly suggests that studies seeking causes for sarcoidosis need to consider both environmental and genetic risk factors to be successful because the two likely interact with each other to produce disease.