The overexpression of genes resulting
from trisomy 21 in Down syndrome may be responsible for many of the
abnormalities of the immune system reported in Down syndrome. The level of superoxide disimutase-1, which is coded by a gene on chromosome
21, is on average, 150% of the values found in normal individuals’ blood
as well as other cells. The high enzyme activity results in a high rate
of conversion of superoxides to peroxides, resulting in high levels
of peroxides that may damage DNA and lipids, and in low levels of the
superoxides that are essential for killing microorganisms such as Staphylococcus
aureus and Candida albicans.
Over expression of lymphocyte function associated antigen-1(LFA-1),
which is also coded on chromosome 21, may lead to an abnormal interaction
between cells from the thymus, resulting in aberrant T-cell maturation
and selection. Overexpression of the interferon receptor gene also located
on chromosome 21 is common in Down syndrome and may also contribute
to immune deficiency. Low serum zinc common in Down syndrome, may
also cause weak immunity.
The most significant abnormality
of the immune system in Down syndrome is a 30-fold increase in the
incidence of acute leukemia and a 200-fold increase in acute megakaryocytic
leukemia. 30% of adults with Down syndrome are deficient in
IgG-2 and/or IgG-4 and these deficiencies are also common in children
with Down syndrome. Elevations of IgG-1 and IgG-3 are common in persons
with Down syndrome. In children with the abnormal immunoglobulin pattern,
selenium supplementation at a dose of 10 mcg/kg (4.54 mcg/lb.) body
weight for six months significantly increased IgG-2 and IgG-4 levels
and reduced the number of infections.
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