DNA test for Down syndrome improved

DNA test for Down syndrome improved

A new test will improve detection of Down syndrome.

A new DNA blood test offers pregnant women a safe and much more accurate way to screen for Down syndrome.

According to a recent study from the Mother Infant Research Institute at Tufts Medical Center in Boston, the test has 10 times better results compared to previous methods, and can be taken as early as the 10th week of pregnancy.

The new test is safe because all it requires is a blood sample from the mother.  New high-speed genetic sequencing is then used to analyze tiny bits of DNA from the baby that float in a woman’s blood when she’s pregnant.

“The blood test is counting sections of DNA, and if there is more DNA than would be expected, it suggests that the baby has an abnormality,” says Diana Bianchi, a pediatric geneticist who led the study.

Down syndrome is a chromosomal disorder caused by an error in cell division that results in an extra 21st chromosome.

Presently it is recommended that all pregnant women be offered a pair of tests – a blood test and an ultrasound to look for fluid at the base of the fetus’ neck – to screen for Down syndrome. These tests yield a large number of false positives, leading to risky invasive tests that sample cells from the fetus.  One of these tests, chorionic villus sampling, has a miscarriage rate of 1 in 200.  The other, amniocentesis, causes miscarriages 1 out of 600 times.

Invasive tests would still be needed to confirm positives from the DNA tests, but they’d be used far less often due to fewer inaccurate results on preliminary tests.  The new DNA test has a false positive rate of only 0.3 percent, while the standard test shows 3.6 percent false positives.

The new DNA test raises some controversy, as pregnant women will be able to decide whether to keep a fetus that shows positive test results for Down syndrome.

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