Heritability versus the role of the environment in autoimmunity.

The higher concordant occurrence of autoimmune diseases in monozygotic twins compared to dizygotic or sibling pairs supports the role for genetic susceptibility. For most conditions, however, concordance rates are considerably below 100% and lead to the estimate of the weight of genetics coined "heritability". In the group of autoimmune diseases heritability ranges between 0.008 and 1 with median values of approximately 0.60. A complementary term coined "environmentability" represents the environmental influence on individual phenotype, and can include dietary habits, chemicals, or hygienic conditions. Genome-wide association data in complex diseases confirmed a role for the environment in disease etiology as significantly associated polymorphisms were found only in subgroups of patients and controls. Environmental links to autoimmunity range from anecdotal associations or case series to largely investigated experimental and epidemiological studies. A bibliographic analysis reveals that the number of publications dedicated to environmental factors in autoimmunity has grown on average by 7% every year since 1997. 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, confidences, and critical knowledge gaps in this area. The results of the workshop discussion are summarized in the articles found in this issue of the Journal of Autoimmunity.