Sarcoidosis develops in genetically predisposed individuals that are exposed to unknown antigens. There is a statistically significant increased risk for the disease among family members of sarcoidosis patients, and the disease differs in different ethnic groups. It is a genetically complex disease, with many genes contributing, both as risk factors but also with an influence on the disease course. The strongest genetic associations with sarcoidosis are found within the major histocompatibility complex (MHC) [human leukocyte antigen (HLA) in humans]-region on chromosome six. This region includes, besides the HLA-class I and class-II genes, a large number of genes important for the immune response and inflammation. The well studied associations between sarcoidosis and HLA-class II molecules indicate specific antigen presentation for T helper cells, which is in agreement with the characteristic finding of lung-accumulated CD4+ T helper cells expressing a limited set of T cell receptors. Strong associations between distinct HLA-DRB1 alleles and the disease phenotype and course have been described, especially so in patient subgroups. Although a large number of genes are associated with sarcoidosis, this review focuses on gene associations and their influence on the disease phenotype, including the disease course.
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