Down syndrome, Trisomy 21

Down syndrome is a congenital chromosomal abnormality that affects about one in 1,000 babies. It is caused by the presence in the affected person's cells of an extra chromosome number 21. It is the most common syndrome involving chromosomal trisomy.

Children with Down syndrome have very characteristic features. The face is flat, and the eyes have an upward slant with prominent folds of skin at the upper inner corners (epicanthal fold). Their hands are short and broad, with a shortened 5th finger and a distinctive single palm crease that traverses the hand (simian crease). Infants with Down syndrome are often noticeably hypotonic (lesser than normal muscle tone).

Children with Down syndrome have varying degrees of mental and growth retardation. They are much more prone to have heart malformations - 30 to 40% of infants with Down syndrome have a heart defect at birth. Intestinal malformations (intestinal atresia - total blockage) are also more common in children with Down syndrome. Leukemia and, in later life, Alzheimer's disease occur more frequently than expected for the general population in persons with Down syndrome.

The incidence of Down syndrome is strongly influenced by maternal age at the time of conception. A 20-year-old mother's risk of having a child with Down syndrome is 0.6 per 1000 live births, a 30-year-old mother's risk is 1.1 per 1000 live births, a 35-year-old mother's risk is 2.65 per 1000 live births, and a 45-year-old mother's risk is 33 per 1,000 live births (that is, about 1 in 30 babies born to 45 year old mothers will have Down syndrome). However, as Dr. Leshin points out, "Advancing maternal age is the only risk factor known to date, but almost half of all babies with Down syndrome are born to mothers under 35 years of age, so there's something else going on we don't about yet."

Most children with Down syndrome have mild to moderate mental retardation (IQ 30 to 60). Persons with Down syndrome at the upper end of the IQ range might attain 4th to 6th grade reading skills. Persons with Down syndrome can provide for basic self-help needs, and have varying degrees of educational achievement and social and occupational skills. They need special education, training facilities, and frequently sheltered living and work situations.

This is just a brief overview of Down syndrome, written for those who do not have a Down child but wish to know a little more about the condition. Many resources exist on the web for parents of Down syndrome children. I suggest you first stop by the website of my friend and former colleague, H. Len Leshin, M.D.

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