Several significant associations have been found between
HLAs and diseases. In many, but not all, of these disorders,
immunologic abnormalities are evident. The HLA complex is
the most diverse and polymorphic genetic system, with major
functional and medical implications. The human MHC gene
cluster spans a region of about 4000 kb on the short arm of
chromosome 6 in the distal portion of the 6p21.3 band (11).
Data from physical mapping, DNA cloning, and sequencing
of the MHC region showed the presence of 224 gene loci, of
which 128 are predicted to be expressed (12). Numerous
investigators have suspected that chronic diseases of the central
nervous system, including schizophrenia, have genetic,
immunologic, and viral etiology (13,14). Many psychiatric
conditions, such as psychosis, depression, and anxiety, have
been considered in autoimmune disorders (15). More interestingly,
one study showed significantly decreased production of
interferon-gamma in acutely ill patients with paranoid schizophrenia,
thereby indicating the possibility of immunologic
dysfunctions in paranoid disorders (16).