The human leucocyte antigens and clinical medicine: an overview.

The Major Histocompatibility Complex (MHC) occupies 4-6 megabases on the short arm of chromosome 6 and is the most intensively studied segment of the human genome. This region was first discovered through its influence on transplantation rejection and on antigen-specific immune responses. The most important genes for managing these functions encode the HLA molecules (human leucocyte antigens) which are highly polymorphic in human populations. HLA typing for these polymorphisms is widely used in clinical medicine when identifying optimal organ donors or recipients and in assessing the risk of diseases such as narcolepsy, hereditary hemochromatosis, ankylosing spondylitis and certain autoimmune disorders. As new genes are identified in the MHC, the clinical impact of this genetic region is likely to assume further importance as outlined in this review.