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DOWN'S SYNDROME
Sarah Rutter (Down's Syndrome Association,
UK)
Down's syndrome is the commonest identifiable cause of intellectual
disability, accounting for around 15-20% of the intellectually
disabled population.
It is believed that people with Down's syndrome have always existed.
However, it was not until 1866 that the English doctor, John Langdon
Down, first described the condition, which subsequently took his
name.
Click here to see a related article about the History
of Down's Syndrome
In 1959 Professor Jerome Lejeune, a geneticist in Paris, discovered
that Down's syndrome occurred as a result of a trisomy of chromosome
21. This means that instead of the usual 46 chromosomes in the
cells of the body, there is an extra chromosome 21, making 47
chromosomes in all. Since then, other forms of the condition,
which are much rarer, have been discovered, such as Translocation
and Mosaicism. Approximately 94% of people with Down's syndrome
have standard trisomy 21, 4% have a translocation and 2% mosaic
Down's syndrome.
In the vast majority of cases, Down's syndrome is not hereditary.
Click here to see a related article about the Genetics
of Down's Syndrome.
What causes Down's syndrome?
As yet we do not know what causes the presence of an extra chromosome
21. It can come from either the mother or the father, but most
commonly from the mother. There is no way of predicting whether
a parent is more likely to produce an egg or sperm with 24 chromosomes.
There is a definite link with advanced maternal age for reasons
yet unknown. However, most babies with Down's syndrome are born
to women under the age of 35, as younger women have higher fertility
rates.
Nothing done before or during pregnancy can cause Down's syndrome.
It occurs in all races, social classes and in all countries throughout
the world. It can happen to anyone.
Incidence
For every 1,000 babies born in the UK, one will have Down's syndrome.
This means that about 600 babies are born with Down's syndrome
each year in the UK. Down's syndrome affects people of all ages,
races, religious backgrounds and economic situations. It is estimated
that there are around 60,000 people with Down's syndrome living
in the UK, but since Down's syndrome has never been a notifiable
condition, accurate figures are difficult to obtain.
How is Down's syndrome diagnosed?
The diagnosis of Down's syndrome is usually made soon after the
birth of the baby because of the baby's appearance. There are
many physical characteristics associated with the condition, which
may lead a parent or midwife, or other medical professional, to
suspect that the baby has Down's syndrome.
Some of the features include:
- Reduced muscle tone which results in floppiness (hypotonia);
- A flat facial profile, flat nasal bridge, small nose;
- Eyes that slant upwards and outwards, often with a fold of
skin that runs vertically between the lids at the inner corner
of the eye (epicanthic fold);
- A small mouth which makes the tongue seem slightly large;
- A big space between the first and second toe (sandal gap);
- Broad hands with short fingers and a little finger that curves
inwards. The palm may have only one crease across it (single
palmar crease);
- A below average birth weight and length at birth;
Many of these features are found in the general population. Therefore
a chromosome test (karyotype) would need to be carried out before
a positive diagnosis could be made. This is done by analysing
the chromosomes in the blood cells.
Do people with Down's syndrome have
medical problems?
Certain health problems are more common in people with Down's
syndrome than in the rest of the population. These include:
- 40-50% of babies with Down's syndrome are born with heart
problems, many of which require heart surgery;
- A significant number of people with Down's syndrome will have
hearing and sight problems;
- Thyroid disorder;
- Poor immune system;
- Respiratory problems, coughs and colds;
- Obstructed gastrointestinal tract.
However, with advances and increased access to medical care most
of these problems are treatable. None of these problems is unique
to people with Down's syndrome - they also occur in the rest of
the population.
It is also important to remember that some people with Down's
syndrome do not experience any health problems.
Advances in treatment and increased access to medical care have
also meant that people with Down's syndrome are living much longer.
Life expectancy is now put at 60-65, and many people with Down's
syndrome live even longer.
How does Down's syndrome affect
development?
All people with Down's syndrome will have some degree of intellectual
disability. Children with Down's syndrome do learn to walk, talk
and be toilet trained but in general will meet these developmental
milestones later than their non-disabled peers. There is a wide
variation in ability in people with Down's syndrome just as there
is in the rest of the population.
Early intervention programmes which help in all areas of child
development are now widespread. These programmes can include speech
and physical therapy as well as home teaching programmes for the
child and the family.
Children and adults with Down's syndrome can and do continue
to learn throughout their lives just like the rest of the population.
Fact or fiction?
Children with Down's syndrome are only born to older parents.
Fiction: 80% of children with Down's syndrome are born
to women younger than 35. However, the likelihood of having a
child with Down's syndrome
does increase with the age of the mother.
Children with Down's syndrome are always happy.
Fiction: People with Down's syndrome have the same feelings
and moods as everyone else.
People with Down's syndrome cannot form relationships.
Fiction: People with Down's syndrome are perfectly capable
of forming all types of relationships with people they encounter
in their lives, be it friendship, love or dislike.
People with Down's syndrome cannot have children.
Fiction: Women with Down's syndrome can and have had children.
It has been recorded that two men with Down's syndrome have become
fathers. The information about fertility in people with Down's
syndrome is very outdated and based on research in institutions
where men and women with intellectual disabilities were kept apart.
All people with Down's syndrome will eventually develop Alzheimer's
disease (dementia).
Fiction: Although many people with Down's syndrome do
develop dementia in their later years, this is by no means inevitable.
Research indicates that the incidence of dementia in people with
Down's syndrome is similar to that of the general population only
that it occurs 20-30 years earlier.
Further information can be obtained
from "People with
Down's syndrome at all Ages" by S. Trumble, "The
Genetics of Down's Syndrome" by A. Kessling & M.Sawtell,
and "The
Immune System in Down's Syndrome" by M.A. Kerr on this
site and from the Down's Syndrome Association website www.dsa-uk.com.
We strongly recommend that you view these and the Down's Syndrome
Medical Interest Group website: www.dsmig.org.uk.
This article was first published on the site in 2002.
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