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Down syndrome

Alternative Names
trisomy 21

Down syndrome is the name for the pattern of physical features and disorders that usually occur from an extra chromosome twenty one. Chromosomes are the materials that store people's genetic information.

What is going on in the body?
Because people with Down syndrome have an extra chromosome, the body's natural balance is upset. This upset in balance leads to various birth defects and problems of growth and development. Many of the birth defects in people with Down syndrome are like those seen in other children. People with Down syndrome simply have birth defects more often than others.

What are the signs and symptoms of the condition?
Problems start before birth in affected people. The following differences can be seen in people with Down syndrome:
  • smaller physical size. Infants with Down syndrome are smaller than average, as are children and adults with Down syndrome.
  • poor muscle tone, which tends to improve somewhat over time.
  • a small head, the back of which is flatter than average.
  • flat facial profile.
  • upward slant of the eye slits.
  • an extra fold of skin at the inner corners of the eyes.
  • small mouth with a tendency to protrude the tongue.
  • short hands with a single crease across the palms.
  • heart defects.
  • learning disabilities.
  • lower intelligence, as measured by an IQ score. The IQ of people with Down syndrome is rarely higher than 50. Normal IQ, by contrast, is around 100.
  • faster ageing process. People with Down syndrome tend to show diseases of ageing, such as Alzheimer's disease, at a relatively early age.
Other physical defects are also possible.

What are the causes and risks of the condition?
Down syndrome is usually caused by an extra chromosome twenty one. Most people have forty-six chromosomes in each cell of their bodies. These chromosomes exist in pairs, for a total of twenty-three pairs. The pair associated with Down syndrome is called pair twenty-one. Why an extra copy of this chromosome causes the features of the Down syndrome is not known. The genetic material on this chromosome pair directs the formation of compounds that the body needs to perform various functions and for development to be normal. The overload of information caused by the extra copy causes problems and leads to the Down syndrome. Scientists have recently identified 99.7% of the genes on this chromosome. Hopefully, this knowledge will lead to a better understanding of the syndrome and, perhaps, even treatments for some of the symptoms.

Down syndrome occurs in roughly one of every 750 births. There is a strong link between the risk of Down syndrome and the age of the mother. The risk of having a child with Down syndrome is less than 1 in 2,500 among young women. This risk increases to roughly 1 in 350 when women reach 35 years of age. After age 45, the risk is roughly 1 in 25.

What can be done to prevent the condition?
Down syndrome is caused by a chromosome problem that is present when conception occurs. Therefore, there is no way to prevent Down syndrome in a person who has already been conceived. Some women may want to have their child screened for Down syndrome during early pregnancy. If screening detects Down syndrome in the child, some women may elect to have an abortion. Genetic counselling is also useful for the families of affected children.

How is the condition diagnosed?
Down syndrome may be suspected at birth when certain physical features or defects are present. A chromosome analysis, however, confirms the diagnosis. There are also tests that screen for Down syndrome during pregnancy. These tests measure certain chemicals in a pregnant woman's blood, among them alpha-fetoprotein. When the chemicals are out of balance, there is a risk that the foetus has Down syndrome and other tests can be ordered to confirm Down syndrome. These tests analyse the chromosomes of tissue taken from the foetus. These tests include chorionic villus sampling and amniocentesis. Also a newer test called the nuchal translucency test is performed using ultrasound between 11.5 and 13.5 weeks gestation, and can detect about 80% of foetuses with down syndrome.

What are the long-term effects of the condition?
The life span for people with Down syndrome is shorter than average. Heart defects are the leading cause of death in infants. Otherwise, 3 of 4 people with Down syndrome reach 30-35 years of age. Common causes of death in older individuals include lung disease, infections, hepatitis, and leukaemia, a cancer of the blood. Chronic infections of the eyes and nose, tooth disease, and thyroid gland problems and diabetes are common at all ages.

What are the risks to others?
Down syndrome is not contagious. While reproduction is possible for some people with Down syndrome, males have not been known to have children and females rarely do. Therefore, the disorder usually is not passed from one affected person to another.

For what is often thought to be genetic reasons, parents who have had one affected child are at slightly higher risk than others to have another affected child. In some cases, the risk may be much higher if the parents have certain genetic problems. For this reason, genetic counselling for families of people with Down syndrome is advised.

What are the treatments for the condition?
There is no treatment for the Down syndrome itself. Treatment is directed toward whatever health and other problems affected people may have. Educational strategies, occupational and physiotherapy, and early childhood intervention programs may all be helpful.

What are the side effects of the treatments?
Side effects depend upon the treatment used. Heart surgery, for example, has more side effects than treatment of ear infections.

What happens after treatment for the condition?
In general, people with Down syndrome function well in society. With good support systems, most can live fairly normal, productive lives.

How is the condition monitored?
Down syndrome does not get worse, except for the ageing process mentioned earlier. Routine health care for children and adults is recommended.

Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.

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