Patau syndrome is associated with severe mental retardation, small eyes that may exhibit a split in the iris (coloboma), a cleft lip and/or palate, weak muscle tone (hypotonia), an increased risk of heart defects, skeletal abnormalities, and other medical problems. Affected individuals rarely live past infancy because of the life threatening medical problems associated with this condition. Patau syndrome affects approximately 1 in 10,000 live births. The risk of having a child with Patau syndrome increases as a woman gets older.

People with Patau syndrome have additional DNA from chromosome 13 in some or all of their cells. The extra material disrupts the normal course of development, causing the characteristic features of Patau syndrome.

Most cases of Patau syndrome result from trisomy 13, which means each cell in the body has three copies of chromosome 13 instead of the usual two copies. A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome 13, resulting in a mixed population of cells with a differing number of chromosomes, such cases are called mosaic Patau syndrome.

Patau syndrome can also occur when part of chromosome 13 becomes attached to another chromosome (translocated) before or at conception. Affected people have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 13 and often the physical signs of the syndrome differ from the typical Patau syndrome.

Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome 13. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each of the body's cells.

Mosaic Patau syndrome is also not inherited. It occurs as a random error during cell division early in fetal development. As a result, some of the body's cells have the usual two copies of chromosome 13, and other cells have three copies of the chromosome.

Patau syndrome due to a translocation can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 13. Although they do not have signs of Patau syndrome, people who carry this type of balanced translocation are at an increased risk of having children with the condition.

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Health test for babies just five weeks into pregnancy
From Evening Standard (London), 7/15/03 by MARK PRIGG

PARENTS could soon be able to genetically screen their unborn child for abnormalities and discover its sex just five weeks into pregnancy.

Based on the same technique as a smear test, which is used to check women for cancer, the new test could be performed by a GP - with results available in less than 24 hours.

It will mean that women will be able to reassure themselves their child is healthy almost as soon as they realise they are pregnant. Currently most expectant mothers must wait until 16 weeks into the pregnancy before they can have a definitive test, and then wait a further three weeks for the result.

During the new test a swab is used to take cell samples from within the womb. DNA testing is then used to isolate the cells of the foetus, which can be screened for a wide range of abnormalities, including Down's Syndrome and cystic

fibrosis.

Parents will, if they wish, also be able to find out the sex of their unborn child.

According to Dr Ian Findlay, a senior scientist at the Australian Genome Research Facility in Brisbane, who has spent the past five years developing the test, its key advantage is that it opens up genetic testing to everyone, not just those in high-risk groups.

"The problem with current tests, apart from the length of time they take, is that often it's only high-risk groups that have them," Dr Findlay said.

"What we can do is make sure, through the ease of use and low cost of our test, that everyone can have access to genetic screening, and have it far earlier than before - which, should there be any problems, is far easier on the parents."

If further clinical trials designed to prove the accuracy of the new test progress well, GPs could begin administering the test within two to three years.

At present, at 11 weeks it is possible to test for Down's, Edwards's and Patau's syndromes by insertinga needle into the womb to take a sample of the placenta.

However, because of the risk of miscarriage, it is usual to wait until the 12-week stage, when a scan can show whether there is a chance the child has Down's or other syndromes. This test is safe and fast but not 100 per cent accurate. Doctors can also tell the sex of the unborn child at this stage.

If there is a risk of the child having an abnormality then, at 16 weeks, the definitive amniocentesis test can be performed. Close examination of the fluid in which the unborn baby floats allows doctors to check all the child's chromosomes. However, using a needle to remove the fluid creates the small risk of a miscarriage and full results take about three weeks.

Rosie Barnes, chief executive of the Cystic Fibrosis Trust, believes the new test could be a godsend for parents. "We would wholeheartedly support any new test which meant more parents have the option to screen their children, especially at an early stage. It could make a big difference to parents' decisions."

However, some doctors have warned that the new test could be too early. Dr Donald Gibb, of the Birth Company in Harley Street, warned that many pregnancies miscarry in weeks five to eight. "I can see this test being very valuable if it is proved to be reliable. However, after week eight you are much more assured of the development of the foetus, and that would seem a more sensible timeframe for testing."

For information and support about prenatal testing call the Antenatal Results and Choices (ARC) helpline on 020 7631 0285.

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