Down syndrome

What is Down syndrome?

Chromosomes contain most of our genetic material. The correct number and arrangement of chromosomes are necessary for the development of a normal individual.

Down syndrome is an abnormality of the chromosomes in which the individual has 3 copies of chromosome 21, rather than the normal 2 copies. For this reason, the condition is also called Trisomy 21.

Children with Down syndrome are born with a characteristic physical appearance that includes slanted eyes, a flat nose on a round head, and abnormalities on the palms of the hands and the soles of the feet. They can have multiple birth defects such as in the bowel and heart and there is a degree of intellectual impairment.

Down syndrome occurs in fewer than one in 1100 births. While older women have a higher risk, women of any age can have a baby with Down syndrome.

Screening tests for Down syndrome

Pregnant women can choose to have antenatal screening tests that identify those at higher risk of having a baby with Down syndrome. It's important to be fully informed since you may be confronted with a decision if the tests come back positive.

Screening testing varies according to when in pregnancy you choose to have it done. Apart from a relatively new genetic test which is highly accurate, but not yet reimbursed in Australia, screening tests give you a percentage chance of carrying a baby with Down syndrome. That helps you and your doctor decide whether to proceed to a diagnostic test such as chorionic villous sampling (CVS) which involves removing some cells from the placenta earlier in pregnancy or, at around 16 weeks, an amniocentesis which samples fluid from around the baby and examines the cells in the fluid. Both these tests carry a small risk of miscarriage.

The screening tests involve a nuchal translucency ultrasound, which measures the width of an area on the back of the neck of the fetus, and maternal blood tests looking at the levels of certain hormones.

Health issues associated with Down syndrome

Down syndrome is often associated with medical problems such as congenital heart disease, hearing loss, hypothyroidism (an under-active thyroid gland), cataracts and obstructive sleep apnoea. In addition, most children with Down syndrome function in the lower range of intellectual abilities.

It is important that children with Down syndrome and their families receive support from their doctor, as well as other health professionals such as physiotherapists and speech therapists.

References

1. Down Syndrome Australia. https://www.downsyndrome.org.au/down_syndrome.html
2. NSW Health. Centre for Genetics Education. Fact Sheet 25: Screening tests during pregnancy. http://www.genetics.edu.au/publications-and-resources/facts-sheets/fact-sheet-25-screening-tests-during-pregnancy/view (updated Jan 2018).
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