It’s the most common birth defect, and the image of cognitive impairment for a lot of people. Down syndrome, or trisomy 21, affects more than one in every 700 babies born in the United States each year. Most people have two copies of each of the 23 chromosomes that make up the human genetic library. A third copy of most chromosomes results in a miscarriage, but the 21st is an exception; however, the presence of a third copy during fetal development typically leads to Down syndrome.
Perhaps the best-known risk factor for Down syndrome is maternal age. When a woman turns 35, the odds that her next child will have Down syndrome increases more than tenfold. If a woman of any age has had a child with Down syndrome, that itself seems to increase the risk of other children having it as well.
Extra chromosomes can be found in utero through prenatal testing. This testing is now routine in prenatal care. That allows expectant parents who know their child will have the condition can have a head start in making whatever preparations they deem necessary—and also to prepare themselves psychologically for the challenge unique to raising a child in these circumstances.
Life expectancy for people with Down syndrome has improved dramatically in a short time. A child born with Down syndrome in 1983 could expect to live, on average, 25 years; by the time that child turned 25, however, babies with Down syndrome could reasonably expect to have a lifespan nearly typical of the general population. However, people with Down syndrome tend to have, in addition to sometimes profound cognitive disability, certain physical characteristics. These include a flat face, a creased palm, poor muscle tone, and small hands and feet.
In addition, children with Down syndrome often have certain atypical medical needs. Down syndrome brings with it an increased risk of medical conditions including Alzheimer’s, trouble breathing, hearing impairment, leukemia, and even heart defects. It’s important to watch for these conditions and start treatment immediately if they do crop up.