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What is Down syndrome?
Down syndrome is the most frequent chromosomal anomaly - it occurs in one in every 546 live births in Ireland.
For some unknown reason, an error in cell development results in 47 chromosomes rather than the usual 46. This extra gene material changes the orderly development of the body and brain.
Down syndrome is one of the most common known causes of intellectual disability.
Each person with Down syndrome is an individual, with a unique appearance, personality and abilities.
Children with Down syndrome benefit from the same care, attention and inclusion in community life that helps every child develop. As with all children, quality education in neighborhood schools, preschools, special schools or at home is important to provide the opportunities that are needed to develop strong social and academic skills.
Children with Down syndrome are creative and imaginative in play and mischief and have the same emotions and attitudes as other children. Many children with Down syndrome may grow up to live independent lives with varying degrees of support and accommodation needed, while others may require ongoing support and more sheltered living accommodation.
Where does the term 'Down syndrome' originate?
Dr John Langdon Down, a physician in London, was the first person to accurately describe the condition in 1866. As a result, the condition today bears his name. He originally named the syndrome 'mongolism' because the upward slant of the eyes was similar to that of people living in Mongolia.
In 1960, Asian genetic researchers objected to the use of the word 'mongoloid'. As a result of this, the name 'Down syndrome' was given to the condition. It is now known as this throughout the world.
What causes Down syndrome?
Down syndrome is caused by an extra copy of the 21st chromosome usually in each cell in the body.
It was in 1959 that Professor Jerome Lejeune in Paris identified the extra chromosome as being the cause of Down syndrome. It is now well understood at the chromosomal level, however the factors responsible for generating chromosome abnormalities are largely unknown.
A baby with down syndrome can be born to any family, to parents of any age, to any race, religion or social background. It is a chromosomal accident, not caused by anything the parents may have done before or during pregnancy.
What are chromosomes?
Chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell in the body and carry the messages or genes which guide the development of a foetus.
They are normally grouped together in 23 pairs i.e. 46 in total. Down syndrome is usually caused by an extra chromosome 21 in either the sperm or the egg. When the affected egg or sperm join to produce the first cell, they will make a cell with 47 chromosomes, three of number 21 instead of two. This is why the usual form of Down syndrome is called 'Trisomy 21'.
The additional chromosome is the result of an error in cell division and the medical term for this accident is 'nondisjunction'. As the baby develops, all the cells grow from this first cell and so all have the extra chromosome.
Are there different types of Down syndrome?
There are three major types of Down syndrome. Your baby will most likely have Trisomy 21 (three of number 21 instead of two). About 95% of people with Down syndrome have Trisomy 21.
About 4% have Translocation, where the extra chromosome 21 broke off and became attached to another chromosome. About 1% have Mosaic type Down syndrome, where only some cells have Trisomy 21.
When a child with Down syndrome is born, one of the first needs of the parents is up to date information about the condition. Down syndrome Ireland has an information folder available in all maternity hospitals for new parents to help meet this need. All parents are welcome to avail of the services of Down Syndrome Ireland. More information is available at...
How is it recognized?
Down syndrome is recognisable at birth because of some typical physical characteristics. Diagnosis is then confirmed by chromosome analysis.
While people with Down syndrome do have features in common, they also closely resemble their parents and family. Each person is an individual with a unique appearance, personality and abilities. The extent to which each child shows the physical characteristics of the syndrome is no indication of his or her intellectual capacity.
The main characteristic physical features include:
-Small differences in the shape and size of the head.
-Almond shaped upward slanting eyes.
-Nasal bridge may be slightly flattened.
-The tongue may be prominent.
-Sometimes there is an extra fold (epicanthal fold) of skin at the inner corner of the eye which tends to disappear in the teen years.
-The hands tend to be short and often have a single crease in the palm. There may also be a wide gap between 1st and 2nd toes.
Does Down syndrome increase the risk of any other conditions?
Several treatable medical complications are more common in some babies with Down syndrome. Heart abnormalities are common, affecting between 40-48% of babies. Sometimes surgical correction is required. For most children, surgery corrects the problem and they go on to lead active lives. However some less common heart conditions are not treatable and do reduce the child's life span.
There is an increased risk of gastrointestinal abnormalities in approximately 12% of babies (tracheo-oesophageal fistula, pyloric and duodenal atresia and stenosis, imperforate anus and Hirschsprung's disease). Almost all of these abnormalities can be corrected surgically.
The most common physical problems which occur in early childhood are hypotonia (floppy muscle tone) and respiratory infections (colds, coughs, ear and throat infections). These may require additional medical care.
Children with Down syndrome are at an increased risk of having hearing and visual impairments in early childhood. Early diagnosis and appropriate interventions will help avoid any serious effects on their developmental progress.
There is an increased risk of thyroid and coeliac disease, diabetes, orthopaedic problems, dental problems (gum disease), leukaemia, obstructive sleep apnoea and epilepsy throughout their life. As a result, screening and ongoing medical management may be necessary.
Overweight and obesity is not inevitable in people with Down syndrome. However like anyone, they will benefit from increased enjoyable daily exercise and a diet rich in fibre and low in calories and fat.
People with Down syndrome are now living into their 70s in Ireland, therefore some may develop Alzheimer's disease. It appears that people with Down syndrome may develop Alzheimer's at an earlier age than the general population (usually after the age of 50 years).
Irish research by Dr. Jeannette Tyrell has shown that several other treatable conditions may mimic dementia. Untreated hypothyroidism, a deficiency of vitamin B12 or folate, high levels of calcium in the blood, sensory loss (particularly visual or hearing loss), bereavement or abuse may lead to regression in skills. Therefore proper assessments for dementia are required to exclude untreated medical or social distress. Many symptoms may be helped by environmental, behavioural and medical intervention (Tyrrell J. 2001).
What are the risk factors?
Nobody knows why some babies are born with Down syndrome. One of the factors known to increase the risk of having a baby with Down syndrome is increasing maternal age. However 80% of babies with Down syndrome are born to mothers under the age of 35.
The chance of having a baby with Down syndrome is one in 1,841 at age 15-19 years, compared to one in 26 at age 45 years or older (Irish study Johnson, Z. 1996).
At age 30, the risk is one in 900. At age 35, it is one in 350 and at age 40, it is one in 100.
The general risk of having a child with Down syndrome in Ireland is one in 546 live births (Johnson, Z. 1996).
Can it be prevented?
Having a child with Down syndrome cannot be prevented. It is important to remember that you are not to blame for your baby having this condition. Nothing you did before or during pregnancy has caused it. It occurs in all races, in all social classes and in all countries throughout the world. It can happen to anyone.
Can a baby with Down syndrome be detected in the womb?
The diagnosis of Down syndrome is made by chromosome analysis. There are four tests available which can help detect if a foetus has Down syndrome. These tests can be discussed with your family doctor or your obstetrician.
Early ultrasound and maternal serum screening are screening tests only. They may show that a pregnancy is at an increased risk, but they are not diagnostic.
Amniocentesis and chorionic villus sampling are accurate diagnostic tests, however, they are invasive tests. This is because they involve taking a sample of cells from the placenta or fluid around the foetus (amniotic fluid). There is a small risk of miscarriage involved with these invasive procedures.
Recently it has been found that early ultrasound at ten to fourteen weeks of pregnancy can give clues as to whether a foetus may have Down syndrome. These clues include a thickening of skin over the neck ('nuchal translucency'). However this does not always indicate that a child has Down syndrome. Because this is not diagnostic, ultrasound is usually followed by the accurate tests of amniocentesis or chorionic villus sampling (CVS).
What is the future for Children with Down syndrome?
Children and adults with Down syndrome greatly contribute to their family and society. Maximisation of every support in development, education and health should be available to enable them to progress to their full potential.
Many learn in regular classrooms and young adults with Down syndrome are beginning to hold diverse jobs, making significant contributions to their communities every day.
Those working in the community are constantly breaking down perceived social barriers.
For more information on Down syndrome, contact Down Syndrome Ireland at 1890 374 374 or click on...
Reviewed: July 10, 2006
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Last Reviewed: 10th July 2006