The major histocompatibility complex (MHC) is an approximately 4 megabase region located
on the short arm of chromosome 6 (6p21); it is also known as the human leukocyte antigen
(HLA) superlocus. MHC encodes the classical and transplantation HLA genes and many
other genes with essential roles for immune function and cellular processes including
genes that are important for nervous system development and function. Although the
MHC represents only a very small part (about .1%) of the human genome its properties
can easily be described as extreme and intricate: most complex, most gene dense, most
polymorphic, second largest contiguous sequence, containing the most disease associations,
and most difficult to analyze. Overall, the MHC contains a minimum of 253 identified
genes: 133 protein coding, 19 gene candidates, 22 noncoding, and 79 pseudogenes. MHC
is historically divided into three regions, and HLA genes are distributed over the
class I and class II regions, which in turn are separated by .7 MB of DNA of class
III region genes, which have no known function in immunity. There are 19 HLA loci
and 19 HLA class 2 loci that both include the classical HLA genes all interspersed
in a complex highly polymorphic genomic sequence in which many loci are in almost
complete linkage disequilibrium, and the region is full of interspersed repeats (
1
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Article info
Publication history
Accepted:
August 4,
2012
Received:
August 3,
2012
Identification
Copyright
© 2012 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
