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One of the most frequent causes of
mild to moderate mental retardation is Down syndrome. It occurs in
about 1 in 900 births, resulting in about 350,000 people with Down
syndrome in the United States. Down syndrome is sometimes called
trisomy 21 because it is usually caused by the presence of a partial
or complete third chromosome at position 21 in the human genome,
when only two are supposed to be there. In about 95% of the cases,
the mother is the source of the extra chromosome, and in the
remaining 5% the father is the source. Down syndrome used to be
called mongolism because of the typical facial characteristics of
those with the syndrome, but that term should no longer be used.
The likelihood of
conceiving a
child with Down syndrome increases with the age of the parents,
especially of the mother. It starts low in women under 35 at about 1
in 400 and increases gradually to 1 in 45 in women over 45. The
reason that these probabilities are much higher than the rate of
births of children with Down syndrome is that many pregnancies of
fetuses with Down syndrome end in miscarriage. It is possible to
test whether a fetus has Down syndrome as early as 8 weeks after
conception. The tests carry only a small risk. If
no test of the fetus is undertaken, but Down syndrome is suspected
in the newborn, several symptoms can be checked. They include low
muscle tone, small nose with a depressed nasal bridge, an upward eye
slant, a single deep crease across the palm, and several other
features with which medical personnel should be familiar. There is
no cure for Down syndrome, but children with the syndrome can
benefit from being treated with care and respect, just as can other
children. They are likely to have a variety of medical problems,
including heart and respiratory problems, but these problems can be
managed. The life expectancy of people with
Down syndrome has increased from 8 or 9 years early in the 20th
century to 55 years at the beginning of the 21st century.
Many people with Down syndrome are able to hold jobs, and some are
able to live independently. All of them deserve a chance to realize
the limit of their potential. Most people with Down syndrome are
alert, responsive, and loving. In most cases they adjust well,
although more slowly than most people. The National Down Syndrome Society
maintains an informative and helpful web site that can be reached by
clicking here. Last updated 12/19/03 |
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