Down syndrome
Introduction
Down syndrome is a genetic disorder that causes mental retardation and other problems. The condition varies in severity, so developmental problems may range from mild to serious. It's named after John Langdon Down, the doctor who first identified the syndrome.
Down syndrome is the most common genetic cause of severe learning disabilities in children, occurring in one in every 800 infants. Every year, as many as 5,000 babies are born with Down syndrome in the United States.
There's no medical cure for this condition. But increased understanding of Down syndrome and early interventions are making a big difference in the lives of both children and adults with Down syndrome.
Signs and Symptoms
Children with Down syndrome have a distinct facial appearance. Though not all children with Down syndrome have the same features, some of the more common features are:
- Flattened facial features
- Protruding tongue
- Small head
- Upward slanting eyes, unusual for the child's ethnic group
- Unusually shaped ears
- Poor muscle tone
- Broad, short hands with a single crease in the palm
- Relatively short fingers
- Excessive flexibility
Causes
Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
Down syndrome is caused by three types of abnormal cell division involving the 21st chromosome. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The three genetic variations that can cause Down syndrome include:
- Trisomy 21. More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells. This form of Down syndrome is caused by abnormal cell division during the development of the sperm cell or the egg cell.
- Mosaic Down syndrome. In this rare form of Down syndrome, children have some cells with an extra copy of chromosome 21, but not all. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
- Translocation Down syndrome. Down syndrome can also occur when part of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 stuck to the translocated chromosome. This form of Down syndrome is uncommon.
Complications
Children with Down syndrome can have a range of complications. These include:
- Heart defects. Approximately 50 percent of children with Down syndrome are born with some type of heart defect. These heart problems can be life-threatening and may require surgery in early infancy.
- Leukemia. Young children with Down syndrome are more likely to develop leukemia than are children who don't have Down syndrome.
- Infectious diseases. Because of abnormalities in their immune systems, kids with Down syndrome are much more susceptible to infectious diseases. For example, their risk of contracting pneumonia is much higher than that of children without this disorder.
- Dementia. Later in life, people with Down syndrome have a greatly increased risk of dementia. Signs and symptoms of dementia often appear before age 40 in people with Down syndrome.
- Other problems. Down syndrome may also be associated with a variety of other health conditions, including gastrointestinal blockage, thyroid problems, hearing loss or poor vision.
Treatment
There's no medical cure for Down syndrome. But children with Down syndrome do benefit from medical help and early interventions, starting in infancy.
If your child has Down syndrome, you'll likely become acquainted with a team of doctors that may include a pediatric cardiologist, a gastroenterologist, a developmental pediatrician and other specialists. These doctors can detect and treat complications of Down syndrome, such as heart defects, gastrointestinal problems and hearing problems.
Your child's care team may also include a physical therapist, speech pathologist, occupational therapist and others. These specialists can help your child develop skills as fully as possible. For example, babies with Down syndrome don't have good muscle tone, so a physical therapist can help your baby learn to roll over, sit up and walk. Meanwhile, a speech pathologist or occupational therapist may help with feeding, hand coordination and language skills.
Ask your doctor about early intervention programs in your area. These specialized programs — in which children with Down syndrome are stimulated at an early age with appropriate sensory, motor and cognitive activities — are available in most states. Programs vary from location to location, but they usually involve therapists and special educators whose goal is to help your baby develop motor skills, language, social skills and self-help skills.
In general, children with Down syndrome usually meet developmental milestones, but it usually takes them a little longer than it does for children without Down syndrome. For example, children with Down syndrome may take twice as long to sit, crawl, walk or say a first word. However, early intervention programs, started as soon as possible, seem to give kids with Down syndrome the best chance of success.
Prevention
There's no way to prevent Down syndrome. However, if you are at high risk of having a child with Down syndrome or you already have one child with Down syndrome, you may wish to consult a genetic counselor before becoming pregnant.
A genetic counselor can help you understand your chances of having a child with Down syndrome. He or she can also explain the prenatal tests you will be offered and help you figure out the pros and cons of testing for your particular situation.
Informations obtained from National Institute of Health.