Environment and autoimmunity: Facts and gaps

Autoimmune diseases are comprehensive models of complex conditions in which an individual’s genetic susceptibility is necessary but not sufficient to explain disease onset, perpetuation, and severity. This is well represented by the variable but invariably incomplete concordance rates for all autoimmune diseases in monozygotic twins. In the broad group of autoimmune diseases, heritability ranges between 0.008 and 1 with median values of approximately 0.60. A complementary term coined "environmentability" may well represent the environmental influence on the individual phenotype and can include dietary habits, chemicals, or hygienic conditions via several molecular and epigenetic mechanisms. Numerous environmental factors have been proposed for systemic and organ-specific autoimmune diseases. The National Institute of Environmental Health Sciences (NIEHS) convened an expert panel workshop to review the body of literature examining the role of the environment in the development of autoimmune disease and to identify conclusions, certainties, and critical knowledge gaps in this area. The results of the workshop and the literature illustrate that several kinds of epidemiological, mechanistic, and model evidence support specific chemical and physical factors as well as infectious agents.