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HLA Genetics (3) There is another important issue related to HLA-typing
of which families should be aware. Because HLA types play a role in our
immune systems' responses, diseases known to have immune dysfunction as
a component can be associated with certain HLA types. The reasons for
these HLA/disease associations are not well understood but are well established
for certain diseases. Specific HLA types have been shown to be risk factors
associated with certain diseases. An example of a different type of disease-associated
risk factor is high blood pressure, which is a risk factor for heart disease.
In HLA-associated disease, other, non-HLA factors may play a role in the
development of disease. For example, individuals that carry HLA-DR3 or
HLA-DR4 allele are about 6-7 times more likely to develop insulin-dependent
diabetes than people in the general population. Environmental factors
(diet, certain infections) and other genes (known or uncharacterized)
play a role in individuals who actually go on to develop diabetes. There
are other HLA types that are even more strongly associated with other
diseases. For example, HLA-B27 carriers are approximately 150 times more
likely to develop ankylosing spondylitis, a degenerative arthritic condition.
Since ankylosing spondylitis is rare (about 0.14% of the population is
estimated to be affected), carriers of HLA-B27 have an averaged 20% chance
of developing the condition. It is important that individuals and family
members who are being HLA-typed for possible bone marrow transplantation
are made aware of the possibility that typing will identify the presence
of a disease-predisposing type. An individual with an HLA type associated
with disease susceptibility should be provided genetic counseling. A genetic
counselor can provide support, explain the significance of the HLA type,
assess family history and other risk factors, offer available information
about prevention or medical follow-up, and discuss the implications for
other family members. <back> |
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