Down's syndrome is a genetic condition known as trisomy, where a person inherits
an extra copy of one chromosome. People with Down's syndrome have three copies of chromosome 21 rather than two. This additional
genetic material changes the finely tuned balance of the body and results in characteristic physical and intellectual features.
It's still not known why this abnormality occurs, and it affects around one in 1,000 babies born in the UK, that works out
to about 600 babies a year.
There are three types of Down's syndrome:
- Regular trisomy 21
- all the cells
have an extra chromosome 21, this is the most common type
- Translocation
- the extra chromosome
21 material is attached to another chromosome and one of the parent's may carry the translocated chromosome without any signs
of the condition themselves. This accounts for around four per cent of all cases.
- Mosaic
- only some of the cells
have an extra chromosome 21. Around two per cent of people with Down's have this type, which tends to result in milder features.
Characteristics
Most people recognise the typically flat facial profile and eyes of those with Down's
syndrome. Other typical facial features include smaller ears, a flat back of the head and protruding tongue. People with Down's
also tend to be shorter than average with poor muscle tone and have short, broad hands with a single crease across the palm.
Medical Problems
A number of medical problems are more common in people with Down's syndrome. Almost
half of those with have heart defects, some of which can be treated, some of which cannot. Many also have stomach problems,
which can make eating difficult, and thyroid gland problems.
Other physical problems include cataracts, hearing and sight problems and a susceptibility
to infection Most suffer from varying degrees of learning disability, which may range from moderate to severe. In later life
there's also an increased risk of leukaemia.
On a positive note children with Down's syndrome are usually happy and extremely
affectionate. Many live well into adulthood, with the average life expectancy being around 60 years.
Care and treatment
At present there is no cure for Down's, but treatment of any accompanying health
problems and support for learning difficulties allows many people with the syndrome to lead relatively normal (what ever that
means) and semi-independent lives. Others, however, need full-time care.
Increased risk of having Down's child
The risk of having a baby with Down's syndrome increases with the age of the mother,
especially over the age of 35. Having a child with Down's syndrome is more likely if a woman already has a child with the
syndrome, or if a close family member has had an affected child. However, most cases are sporadic (the parents aren't affected)
and the risk of recurrence in further pregnancies is very small. It does not discriminate, Down's syndrome affects people
from all ethnic groups and cultures.
Antenatal screening
It's not possible to prevent the genetic abnormality that causes Down's syndrome,
but in recent years it has become possible to identify more accurately during pregnancy those babies most at risk. In most
antenatal clinics, women are routinely offered a blood screening test (the triple test) from 14 weeks of pregnancy, which
measures the level of specific substances in the blood. The results are combined with a woman's age at her expected date of
delivery to give an estimated level of risk of Down's syndrome.
Another method of screening available in some hospitals is the nuchal translucency
test. This is an ultrasound scan performed between 10 and 13 weeks of pregnancy, which measures the amount of fluid at the
back of the baby's neck. It's important for women to realise that both forms of screening only identify those women who are
at an increased risk of having a baby with Down's; it doesn't tell them whether their baby has Down's or not.
Those women who are found to be at a higher risk of having a baby with Down's syndrome
are offered the opportunity of further tests to establish whether their child has Down's or not. The tests offered may be
amniocentesis or chorionic villus sampling. These do provide a definitive answer.
Screening for Down's syndrome isn't compulsory. Women are offered screening if they
wish to know whether they're at an increased risk of having a baby with Down's syndrome. If they are, they can then decide
whether to have a definitive test. If this test confirms Down's syndrome, women can then make an informed decision about continuing
with their pregnancy or not.
For more information and support,
The Down's Syndrome Association
Tel: 0845 230 0372 Website: www.downs-syndrome.org.uk
