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.
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.downs-syndrome.org.uk/ 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. Reviewed in 2019, content continues to be relevant.