February 2, 2007 / 12:07 AM / 12 years ago

New Down's test eliminates miscarriage risk

LONDON (Reuters) - A new non-invasive test that examines fetal DNA can pick up genetic abnormalities such as Down’s syndrome, researchers said on Friday.

A pregnant woman is seen in a 2004 file photo. A new non-invasive test that examines fetal DNA can pick up genetic abnormalities such as Down's syndrome, researchers said on Friday. REUTERS/Mykhailo Markiv

Unlike more intrusive tests that may raise the risk of miscarriage, the new diagnostic tool developed by the US company Ravgen poses no threat to the mother or fetus.

It uses fetal DNA extracted from blood samples taken from the mother to screen for chromosomal abnormalities. In a preliminary study of 60 pregnant women reported online by The Lancet medical journal the test produced promising results.

“Right now in the market there is no test available that can reliably do what we do in this study which is, without needing any invasive procedure, to determine whether a baby has an abnormality or not,” said Ravinder Dhallan, lead author of the study and the head of Ravgen.

The blood test correctly diagnosed Down’s syndrome, one of the most common genetic abnormalities, in two cases. It also produced a false positive and a false negative.

Down’s Syndrome occurs when a baby inherits three copies of chromosome 21 instead of two. The risk of having a Down’s baby increases with maternal age.

Dhallan said the test can be adapted to look for abnormalities in any chromosome or single gene disorders.

“In this paper we show proof of principle of how this technology works,” he told Reuters.

Women 35 years and older have been advised to have genetic testing for Down’s syndrome and other disorders. But recently the American College of Obstetricians and Gynaecologists has recommended that all women be given the option of having genetic testing.

Standard tests to detect Down’s syndrome include chorionic villus sampling (CVS) and amniocentesis. CVS, which is performed in the first 13 weeks of pregnancy, analyses placenta cells to detect any genetic abnormalities.

Amniocentesis is usually done at about 16 weeks and involves inserting a needle to withdraw a small amount of amniotic fluid.

The new test detects genetic abnormalities in the fetus by looking at single nucleotide polymorphisms, or SNPs, which are tiny variations in DNA.

Dhallan said he envisions the new test being used along with other tests. Results are available in two to four days.

In a commentary in The Lancet, French doctors said the results are encouraging but larger studies need to be done.

“Dhallan’s test is promising and opens a new era in prenatal diagnosis but to be optimally used as a routine prenatal screening or diagnostic test, their findings need to be replicated in a large-scale multicenter setting,” said Alexandra Benachi, of the Hospital Necker-Enfants Malades in Paris and Jean-Marc Costa, of the American Hospital of Paris.

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