Down Syndrome

Down syndrome is a congenital (present at birth) disorder characterized by varying degrees of mental retardation and a variety of physical abnormalities.

Cause

Normally, each cell in the human body has 46 chromosomes; the cells in someone with Down syndrome, however, have 47. In ways not yet known, the presence of the extra chromosome causes all of the unusual characteristics of Down syndrome. In 95 percent of cases, the condition is called trisomy 21 (because the extra chromosome is attached to the 21st pair of chromosomes), and the mistake in genetic coding is one that apparently could happen to anyone.

Symptoms

Down syndrome is marked by a number of physical characteristics: somewhat slanted eyes in small sockets (which is why it used to be called mongolism); a small, short head, flattened in back and front; a nose flattened at the bridge; a thick tongue; short hands, feet, neck, trunk, arms, and legs; a single, rather than a double, crease across the top of the palm; flabby arms and legs with poor muscle tone; a wide gap between the first and second toes; and generally retarded physical development.

A child with Down syndrome may have a poorly functioning thyroid gland (which regulates metabolism, the rate at which the body uses energy) and pituitary gland (which regulates other glands, including those responsible for growth, maturation, and reproduction). Children with Down syndrome are at much higher risk of developing leukemia, and approximately one-third of them are also especially susceptible to infection.

Education

Characteristically slower than other children to walk, talk, and learn, youngsters with Down syndrome benefit from "early intervention" programs designed to help them develop their abilities as much as possible. Such programs are frequently available from the time the mother and baby leave the hospital after the birth. A number of organizations exist to promote such programs and assist parents in developing their child's potential.

The degree of retardation that accompanies Down syndrome ranges from mild to severe (the average IQ is about 50), and the extent to which a person will be affected cannot be predicted at birth. Some children with the syndrome attend special education classes in public schools; others attend special schools for the mentally retarded. As adults, some may be able to live independently and work in the community. Depending on the degree of retardation that is present, others will require more supervised living arrangements and may be able to hold simple, routine jobs.

Prevention

Prospective parents can reduce their chances of having a child with Down syndrome by starting their families early. At age 20 a woman's risk of giving birth to a child with Down syndrome is only 1 in 2,000 live births, but at age 35 the risk is 1 in 300, at age 40 it is 1 in 100, and at age 45 it is 1 in 40 live births. The age of the father also has some bearing on the risk, but not as much as the age of the mother. Diagnosis of Down syndrome can be made between weeks 16 and 18 of pregnancy through a procedure called amniocentesis. During amniocentesis, the doctor will insert a needle through the mother's abdominal wall and into the uterus. A sample of the amniotic fluid is then drawn into a syringe, grown on a special culture plate, and analyzed to see if there are abnormal chromosomes.

A technique used to check the chromosomes of the growing fetus is called chorionic villus sampling. This procedure, performed during the eighth or ninth week of pregnancy, involves the removal of a small portion of the placenta by a small instrument that is inserted through the woman's cervix. Tissue that is obtained can be immediately evaluated for the presence of chromosome abnormalities.