Genetics in autoimmune hepatitis.

Current hypotheses suggest that autoimmune hepatitis (AIH) is triggered by an environmental factor in a genetically susceptible host. Multiple genes may interact to produce a "permissive gene pool" that determines both disease risk and phenotype. Studies of type 1 AIH have focused on the major histocompatibility complex (MHC), mapping susceptibility to the DRB1 region. Three different molecular models have been proposed based on histidine at DRbeta13, lysine at DRbeta71, and valine at DRbeta86. Although the lysine-71 model has been adapted to explain data from several other studies, the DRbeta13 and DRbeta86 models are exclusive to their founder populations. It is possible that all three models apply and that the different associations reflect the "molecular footprint" of the common environmental triggers in the different study populations. Studies outside the MHC have identified the CTLA4 A+49G, G allele as a possible second risk allele. There are many neutral polymorphisms in the genome, and further studies are currently needed to identify other disease alleles in type 1 AIH.