Epidemiology of sarcoidosis: recent advances and future prospects.

Sarcoidosis is by definition a disease of "unknown causes," but recent epidemiologic advances suggest that the long-standing definition of sarcoidosis may soon need to be amended. The recently completed ACCESS (A Case-Control Etiologic Study of Sarcoidosis) study was not able to definitively identify the "cause" of sarcoidosis, but yielded important findings regarding familial and environmental risks that have advanced our understanding of this disease. The HLA-DRB1 associations reported in ACCESS along with the results of two recently completed genome scans of sarcoidosis in German Caucasians and African-Americans, respectively, have further defined the genetics of sarcoidosis. These studies suggest genetic heterogeneity of sarcoidosis risk between Caucasians and African-Americans and multiple susceptibility genes that interact together and with environmental factors in the disease pathogenesis. Genes that influence sarcoidosis clinical phenotypes may also be largely separate from sarcoidosis susceptibility genes. Although genetic studies of sarcoidosis in African-American populations are confounded by Caucasian admixture, this same admixture may be useful in identifying sarcoidosis genes linked with African ancestry. Case-only methods may be useful in identifying recent acute exposures linked to disease, genetic variants of risk, and gene-environment interactions. In summary, the epidemiology of sarcoidosis has a promising future that should eventually provide the answers to the etiologic origins of this complex disease.