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Accurate blood test for Down syndrome

Woman having ultrasound scan

Currently, pregnant women undergo a set of screening tests that include ultrasound and blood samples (Source: iStockphoto)

Genetic test Pregnant women may soon be able to have a blood test to predict whether their babies are likely to have Down Syndrome instead of undergoing risky, invasive tests, scientists said on Sunday.

In a study in the Nature Medicine journal researchers from Cyprus say a trial on 40 pregnancies using the test, which involves analysing the woman's blood to detect DNA differences between the mother and the foetus, showed it accurately predicted which foetuses were at risk of developing the syndrome.

Philippos Patsalis, medical director of the Cyprus Institute of Neurology and Genetics, who led the study, says the results are "very exciting".

"We believe we can modify this test and make it much easier and simple... (and then) we can have something ready to be introduced into the clinic," says Patsalis.

Down syndrome is the most common genetic cause of mental retardation, occurring in 1 out of 700 live births worldwide. It occurs when a child has three copies of chromosome 21 instead of the normal two and is known as trisomy 21.

The risk of having a baby with Down syndrome increases sharply as women get older. The risk for a 40-year-old mother is 16 times that for one who is 25.

Currently, pregnant women undergo a set of screening tests that include ultrasound and blood samples. For example, one test measures the level of a protein known as PAPP-A in the mother's blood. Low levels of the protein typically indicate that the foetus has Down syndrome.

A positive screening test usually results in an invasive procedure such as amniocentesis (collecting aminotic fluid) or chorionic villus sampling (biopsy of the placenta) or to check whether a baby is likely to be born with Down syndrome . Both tests carry a risk of miscarriage.

Scientists have been looking for new less invasive ways to test for Down syndrome and other potential genetic problems.

Accurate, direct measure

Patsalis' method directly detects trisomy 21 by taking a small amount of blood from the mother when she is between the 11th and 13th week of her pregnancy. The researchers then measured differences in the DNA methylation patterns, which are important to control levels of genes, between mother and foetus.

In a small trial, Patsalis' team were able to correctly diagnose 14 cases where there were extra copies of the chromosome, and 26 normal foetuses - results they say highlight its clinical potential.

"The test is the first worldwide to demonstrate 100 per cent sensitivity and 100 per cent specificity in all normal and Down syndrome pregnancies examined ," the scientists write.


According to the researchers, the test will soon be trialled in a larger study of about 1000 pregnancies, and could lead to changes in clinical practice within two years.
