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Down syndrome or trisomy 21 (usually Down's Syndrome in British
English) is a genetic disorder caused by the presence of all or
part of an extra 21st chromosome. It is named after John Langdon
Down, the British doctor who described it in 1866. The condition is
characterized by a combination of major and minor differences in
body structure. Often Down syndrome is associated with some
impairment of cognitive ability and physical growth as well as
facial appearance. Down syndrome is usually identified at
birth.
Individuals with Down syndrome can have a lower than average
cognitive ability, often ranging from mild to moderate mental
retardation. Developmental disabilities often manifest as a
tendency toward concrete thinking or naïveté. A small number have
severe to profound mental retardation. The incidence of Down
syndrome is estimated at 1 per 800 to 1,000 births.
Many of the common physical features of Down syndrome also appear
in people with a standard set of chromosomes. They include a single
transverse palmar crease (a single instead of a double crease
across one or both palms), an almond shape to the eyes caused by an
epicanthic fold of the eyelid, shorter limbs, poor muscle tone, and
protruding tongue. Health concerns for individuals with Down
syndrome include a higher risk for congenital heart defects,
gastroesophageal reflux disease, recurrent ear infections,
obstructive sleep apnea, and thyroid dysfunctions.
Early childhood intervention, screening for common problems,
medical treatment where indicated, a conducive family environment,
and vocational training can improve the overall development of
children with Down syndrome. Although some of the physical genetic
limitations of Down syndrome cannot be overcome, education and
proper care will improve quality of life.
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