What Is Down Syndrome?
Down syndrome is the term for a set of cognitive and physical symptoms that can result from having an extra copy or part of a copy of chromosome 21.
Down syndrome is the most frequent chromosomal cause of mild to moderate intellectual disability, and it occurs in all ethnic and economic groups.
The degree of intellectual disability in people with Down syndrome varies but is usually mild to moderate. Generally, children with Down syndrome reach key developmental milestones later than other children.
According to the Centers for Disease Control and Prevention, approximately 6,000 babies are born in the United States each year with Down syndrome, or approximately 1 out of every 691 live births.
In recent decades, thanks to appropriate support and treatment, life expectancy for people with Down syndrome has increased dramatically: from 25 years in 1983 to more than 60 years today.
What Causes Down Syndrome?
Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21.
Usually, when one cell divides in two, all pairs of chromosomes are split so that one of the pair goes to one cell, and the other goes to the other cell. But in rare cases, both chromosomes from a pair go together into one cell.
Most of the time, the error occurs at random during the formation of an egg or sperm. No action by parents or environmental factor is known to cause Down syndrome.
After much research on these cell division errors, researchers know that:
- In more than 90 percent of cases, the extra copy of chromosome 21 comes from the mother in the egg.
- In about 4 percent of cases, the father provides the extra copy of chromosome 21 through the sperm.
- In the remaining cases, the error occurs after fertilization, as the embryo grows.
Researchers also know some, but not all, of the risk factors for Down syndrome. For example, parents who have a child with Down syndrome or another chromosomal disorder, or who have a chromosomal disorder themselves, are more likely to have a child with Down syndrome.
In addition, the likelihood that an egg will contain an extra copy of chromosome 21 increases significantly as a woman ages. Therefore, older women are much more likely than younger women to give birth to an infant with Down syndrome.
Still, about 60 percent of babies with Down syndrome are born to women under age 35.
What Are Some Symptoms Related to Down Syndrome?
Symptoms of Down syndrome vary from person to person. Common physical symptoms include:
- Decreased or poor muscle tone
- Short neck, with excess skin at the back of the neck
- Flattened facial profile and nose
- Small head, ears and mouth
- Upward slanting eyes, often with a skin fold that comes out from the upper eyelid and covers the inner corner of the eye
- Single crease across the palm of the hand
- Deep groove between the first and second toes
Physical development in children with Down syndrome is often slower than development of children without Down syndrome. For example, because of poor muscle tone, a child with Down syndrome may be slow to learn to turn over, sit, stand, and walk.
Despite these delays, children with Down syndrome can learn to participate in physical exercise and similar activities like other children. It may take children with Down syndrome longer than other children to reach developmental milestones, but they will eventually meet all or many of them.
Intellectual and Developmental Symptoms
Cognitive impairment—which means problems with thinking and learning—is common in people with Down syndrome and usually ranges from mild to moderate. Down syndrome is only rarely associated with severe cognitive impairment.
Common cognitive and behavioral problems may include:
- Short attention span
- Poor judgment
- Impulsive behavior
- Slow learning
- Delayed language and speech development
In addition, people with Down syndrome are at increased risk for a range of other health conditions, including Autism Spectrum Disorders, problems with hormones and glands, hearing loss, vision problems, and heart abnormalities.
From Weak to Strong
When Andy was little, he didn’t have a lot of muscle control. So his mother decided to try exercising and playing with Andy in the water in an effort to strengthen him. Within four weeks, his muscles got strong, then stronger. Andy started pulling himself up and began to crawl.
At age 6, Andy started training for Special Olympics and has been a part of Special Olympics for more than 20 years. His skills and speed have earned him plenty of medals and recognition at Special Olympics events as well as in other swimming competitions. For example, Andy has competed in U.S. Masters Swimming (USMS) Competitions—alongside International Swimming Hall of Fame members, International Masters Swimming Hall of Fame members, and USMS national and world record holders.
As Andy puts it, “Down syndrome doesn’t matter to me at all.”
Fighting Low Expectations
When Nandi was born, doctors told her parents their child would probably never talk, walk or even be toilet-trained. She is legally blind and has Down syndrome.
Born in the United Arab Emirates, Nandi joined Special Olympics at the age of 9 after the family moved to the U.S. It opened up a whole new world. As she wrote in her journal, “After I came to Special Olympics, I don’t feel lonely any more.”
As Nandi trained in various sports and developed a range of skills, she also developed confidence as she was able to accomplish more and more, event by event, including track and field, roller skating, sailing, ice skating, hockey and even basketball. “She can shoot a mean basketball,” reports her mom. “I don’t know how she does it.”
Nandi's many accomplishments—including having her own business—are helping to change attitudes and educate others about people with Down syndrome. Special Olympics has also encouraged Nandi to become a public speaker—and she makes a special effort to reach out to families of children with intellectual disabilities. Her mom says Nandi has an inspiring way of talking to families who had been told the worst, who now see positive possibilities ahead. Her mother says, “I can hear her talking to them, ‘Don’t cry: My mom says I’m a blessing—and your child will be a blessing, too.’”
Sources: The Eunice Kennedy Shriver National Institute of Child Health and Human Development/National Institutes of Health, the American Association of Intellectual and Developmental Disabilities, and the Centers for Disease Control and Prevention, and Special Olympics.