Proposed model for development of sarcoidosis. Individuals inherit a spectrum of genetic polymorphisms that may influence susceptibility to disease, but that are only realized in the context of a relevant exposure. Disease-associated susceptibility genes may influence position on this matrix differentially, depending on the function of the individual gene product, and on the influence of gene-gene interactions. The relevance of environmental exposures may be influenced by their duration, intensity, timing or context. A similar model might also describe disease phenotype.