Test for Genetic Abnormalities

Test for Genetic Abnormalities A new non-invasive test that examines foetal DNA can pick up genetic abnormalities such as Down's syndrome, say researchers.

Unlike more intrusive tests that might raise the risk of miscarriage, the new diagnostic tool developed by the United States company Ravgen posed no threat to the mother or foetus.

It used foetal 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.

Ravinder Dhallan, lead author of the study and the head of Ravgen, said: "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."

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 takes place when a baby inherits three copies of chromosome 21 instead of two. The risk of having a Down's baby increased with maternal age.

Dhallan said the test could be adapted to look for abnormalities in any chromosome or single gene disorders. He said: "In this paper, we show proof of principle of how this technology works."

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

Standard tests to detect Down's syndrome included chorionic villus sampling (CVS) and amniocentesis. CVS, which was performed in the first 13 weeks of pregnancy, analysed placenta cells to detect any genetic abnormalities.

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

The new test detected genetic abnormalities in the foetus by looking at single nucleotide polymorphisms, or SNPs, which were tiny variations in DNA.

Dhallan said he envisioned the new test being used along with other tests. Results were available in two to four days. In a commentary in The Lancet, French doctors said the results were encouraging, but larger studies needed to be done.

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