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
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
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
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
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
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
-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
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
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...