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The Star Online: Lifestyle: Health

Trisomy 21

Posted: 12 Feb 2014 03:00 PM PST

Down Syndrome or Trisomy 21 is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.

MY new neighbours moved in recently, and I noticed their daughter has Down's Syndrome. What is Down's Syndrome?

Actually, it is called Down Syndrome and not Down's Syndrome.

Down Syndrome is a genetic disorder. It is associated with developmental delays, mental retardation and many other problems.

It is the most common genetic cause of learning disabilities in children, and varies from person to person in severity.

What do you mean by a genetic disorder?

Every one of the cells in your body has a nucleus and cytoplasm. Genetic material – your DNA – is stored in the nucleus in chromosomes, which are rod-like structures that are grouped together.

Each nucleus normally contains 23 pair of chromosomes. Half of these are inherited from your father, and the other half, from your mother.

In Down Syndrome, a person has a full or partial extra copy of chromosome 21. This is called Trisomy 21 (tri = three). This is caused by abnormal division of either the sperm or egg cell.

However, Trisomy 21 is not the only way to get Down Syndrome. It is the reason for 90% of all cases, but there are two other ways, called mosaic Down Syndrome and translocation Down Syndrome.

Is Down Syndrome very common? I heard it is quite common in children of women who get pregnant after 40 years of age.

Down Syndrome is the most common genetic condition in the world. In the United States, the incidence is approximately one out of every 691 babies.

It is true that as you age, having a child becomes more risky for a host of things, including Down Syndrome, to occur.

The risk factors for having a child with Down Syndrome are:

> Having a child when you are older. This is because older eggs carry a greater risk of improper chromosome division. When you are 35 years old, your risk of having a child with Down Syndrome is one in 400. When you are 45 years old, the risk becomes one in 35. It must be said that most Down Syndrome children are born to mothers below age 35 because that group tends to have a lot more children than women over 45.

> If you have a child with Down Syndrome, you are more likely to have another child with Down Syndrome.

Was Down Syndrome discovered by a man named Down?

Down Syndrome probably existed a long time ago, though it was probably not as common then because women tended to have babies very early, and they also tended to die early.

However, it was a man called John Langdon Down who actually published it in 1866. He was a British physician. He described it accurately and as a separate condition, and that is why the syndrome bears his name.

How do I recognise someone with Down Syndrome?

A baby who has Down Syndrome can be of average size at birth. But they tend to grow slowly and remain shorter than other children of similar age. They also hit developmental milestones later too, and start to crawl and sit up later.

A child with Down Syndrome has a distinct facial appearance. It used to be described as "Mongoloid", but that term has now been discarded because of it's derogatory connotations.

These features include:

> Flattened facial features

> Small head

> Protruding tongue

> Short neck

> Upward slanting eyes

> Unusually shaped ears

> Poor muscle tone

> Broad, short hands with only one crease on the palm, unlike a normal palm which has a lot of creases

> Short fingers

> Unusual flexibility

Do people with Down Syndrome tend to die early?

They used to, but modern medicine has made great advances. A century ago, a baby born with Down Syndrome couldn't live past age 10. Now, one can expect to live past 50.

Of course, this depends on how many health problems the person has. Children with Down Syndrome have complications that can become worse when they get older, including:

> Heart defects: happens in half the children. If not treated, this can lead to an early death.

> Leukaemia

> Infectious diseases (these are more likely to develop than in normal children)

> Sleep apnoea

> Obesity

> Dementia

Dr Y.L.M. graduated as a medical doctor and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, e-mail The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.


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