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 DIABETES is a chronic metabolic disorder
that adversely affects the body's ability to manufacture and use
insulin, a hormone necessary for the conversion of food into energy. The
disease greatly increases the risk of blindness, heart disease, kidney
failure, neurological disease and other conditions for the approximately
16 million Americans who are affected by it. Type I, or juvenile onset
diabetes, is the more severe form of the illness.
Type I diabetes is what is known as a 'complex trait', which
means that mutations in several genes likely contribute to the disease.
For example, it is now known that the insulin-dependent diabetes
mellitus (IDDM1) locus on chromosome 6 may harbor at least one
susceptibility gene for Type I diabetes. Exactly how a mutation at this
locus adds to patient risk is not clear, although a gene maps to the
region of chromosome 6 that also has genes for antigens (the molecules
that normally tell the immune system not to attack itself). In Type I
diabetes, the body's immune system mounts an immunological assault on
its own insulin and the pancreatic cells that manufacture it. However,
the mechanism of how this happens is not yet understood.
About 10 loci in the human genome have now been found that
seem to confer susceptibility to Type I diabetes. Among these are (1) a
gene at the locus IDDM2 on chromosome 11 and (2) the gene for
glucokinase (GCK), an enzyme that is key to glucose metabolism which
helps modulate insulin secretion, on chromosome 7.
Conscientious patient care and daily insulin dosages can
keep patients comparatively healthy. But in order to prevent the
immunoresponses that often cause diabetes, we will need to experiment
further with mouse models of the disease, and advance our understanding
of how genes on other chromosomes might add to a patient's risk of
diabetes.
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