Individuals with Down syndrome tend to have a lower-than-average cognitive ability, often ranging from mild to moderate disabilities. A small number have severe to profound mental disability. The average IQ of children with Down syndrome is around 50, compared to normal children with an IQ of 100.
[3] The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although it is statistically much more common with older mothers. Other factors may also play a role.
Many of the common physical features of Down syndrome may also appear in people with a standard set of chromosomes, including
microgenia (an abnormally small chin),
[4] an unusually round face,
macroglossia[5] (protruding or oversized tongue), an almond shape to the eyes caused by an
epicanthic fold of the eyelid, upslanting
palpebral fissures (the separation between the upper and lower eyelids), shorter limbs, a
single transverse palmar crease (a single instead of a double crease across one or both palms, also called the Simian crease),
poor muscle tone, and a larger than normal space between the big and second toes. 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.
[6]