Adult Down Syndrome

UT Southwestern Medical Center researchers are leaders in learning more about Down Syndrome and understanding how to care for persons with the genetic disorder. UT Southwestern and Children’s Health specialists work together in the only Down Syndrome Clinic in North Texas.

Diagnosed in infancy, Down Syndrome is a genetic disorder that includes a combination of birth defects, including some degree of mental retardation, characteristic facial features, and often, heart defects, visual and hearing impairment, and other health problems. The severity of these problems varies.

Down Syndrome is one of the most common genetic birth defects, affecting approximately one in about 800 to 1,000 babies. There are more than 400,000 individuals with Down Syndrome in the United States.

Medical care is focused on treating the health, intellectual, and social challenges associated with the disorder. There is no cure for Down Syndrome.

What Causes Down Syndrome?

Normally in reproduction, the mother’s egg cell and the father’s sperm cell start out with 46 chromosomes. The egg and sperm cells divide and the 46 chromosomes are divided in half, leaving the egg and the sperm cells with 23 chromosomes apiece. When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby ends up with a complete set of 46 chromosomes, half from the father and half from the mother.

Sometimes, an error occurs when the 46 chromosomes divide in half and an egg or sperm cell keeps both copies of the No. 21 chromosome instead of just one copy. If this egg or sperm is fertilized, the baby ends up with three copies of the No. 21 chromosome, which is called trisomy 21 or Down Syndrome. The features of Down Syndrome result from having an extra copy of chromosome 21 in every cell in the body.

Types of Down Syndrome

Ninety-five percent of Down Syndrome results from trisomy 21. Occasionally, the extra chromosome 21 or a portion of it is attached to another chromosome in the egg or sperm. This may result in Translocation Down Syndrome, which occurs in 3 percent to 4 percent of cases. This is the only form of Down Syndrome that may be inherited from a parent.

In 1 percent to 2 percent of cases, a form of the disorder called Mosaic Down Syndrome may occur when an error in cell division occurs after fertilization. These individuals have some cells with an extra chromosome 21 and others with the normal number.

Physical Features

A person with Down Syndrome will have some, but not all, of these features:

• Eyes that slant upward and small ears that may fold over slightly at the top
• Small mouth, making the tongue appear large
• Small nose with flattened nasal bridge
• Short necks, small hands, and short fingers
• One single crease in the palm that goes straight across, and a second crease that curves down by the thumb
• Short in stature with unusually loose joints

Health Problems

Individuals with Down Syndrome have a variety of health problems, including:

• Heart defects: Found in 40 percent to 60 percent of people with Down Syndrome; some minor and treatable with medication; some serious and requiring surgery
  
• High incidence of infection: Greater frequency of colds, bronchitis, sinus infections, and pneumonia
  
• Increased risks: More likely to have thyroid problems or leukemia
  
• Intestinal malformations: Intestinal blockages or other problems that require surgery in about 12 percent of Down Syndrome patients
  
• Loss of mental functioning: Alzheimer-like issues, such as memory loss, more likely with aging
  
• Visual or hearing impairment: Includes crossed eyes, nearsightedness, farsightedness, and cataracts, most correctable
  

Despite their health problems, many adults with Down Syndrome are able to have jobs and live independently. Life expectancy for individuals with Down Syndrome is about 60 years.