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Down's syndrome blood test more accurate than existing screening

13 April 2015

By Kirsty Oswald

Appeared in BioNews 797

Research shows that a new prenatal blood test for Down's syndrome outperforms current methods of screening.

The test, developed by the Roche-owned Ariosa Diagnostics, correctly identified all instances of Down's syndrome in the study, with a false-positive rate a fraction of that seen with the existing first trimester combined test.

The researchers say that the accuracy of the test could mean fewer pregnant women have to undergo amniocentesis, which carries a one in 100 risk of miscarriage.

The team, from the University of California, San Francisco, studied over 15,000 women who underwent standard screening for Down's syndrome at weeks 10 to 14 gestation, as well as the new cell-free DNA (cfDNA) test.

They report in the New England Journal of Medicine that the cfDNA test identified all 38 cases of Down's syndrome that were later confirmed by diagnostic genetic testing or examination at birth, giving a 100 percent sensitivity. This compared with the detection of 30 cases, and a sensitivity of 78.9 percent, with standard testing.

Furthermore, cfDNA testing produced a false-positive rate nearly 100 times lower than that of standard screening; there were only nine false-positives compared with 854 with standard screening.

The cfDNA test also detected nine of the 10 cases of Edward's syndrome (trisomy 18) and both cases of Patau's syndrome (trisomy 13) in the study sample.

Current screening procedures for Down's syndrome and other aneuploidies consist of blood biochemistry and ultrasound to assess nuchal translucency. However, when a positive result is found, amniocentesis is needed to confirm the diagnosis.

The new test, marketed as Harmony, analyses the small percentage of fetal DNA that is found floating in a pregnant woman's plasma. Increased quantities of DNA from certain chromosomes, such as 21 in the case of Down's syndrome, can indicate chromosomal abnormality.

Last month, Great Ormond Street Hospital in London announced that it would begin offering a non-invasive prenatal test for Down's syndrome and other trisomies, developed through the NHS's RAPID (Reliable Accurate Prenatal Non-Invasive Diagnosis) Project.

Discussing the new research findings, Professor Lyn Chitty from the Hospital told the BBC: 'These are really exciting times; this cell-free DNA is changing prenatal care dramatically.

'I think it broadens access to testing. Really, a number of women will decline invasive testing because of the risk of miscarriage and they may well take up non-invasive prenatal testing.'

Both tests are to be assessed by the UK's national Down's syndrome screening programme and a decision over whether they are rolled out nationally in the NHS is due in June.


03 October 2016 - by Victoria Woodham 
The introduction of non-invasive prenatal testing in the NHS screening programme for pregnant women may seem like a no-brainer, but it is based on outdated ideas of what life is like for people with Down's syndrome and their families...
04 April 2016 - by Helen Robertson 
The presence of genetic abnormalities in cells taken from the placenta at the early stages of pregnancy does not necessarily mean that a baby will be born with a genetic disorder, a study in mice suggests....
18 January 2016 - by Lone Hørlyck 
A new blood test for Down’s syndrome in high-risk women has been recommended for use on the NHS....
20 July 2015 - by Ceri Durham 
Abnormal results from a non-invasive prenatal test for fetal chromosome abnormality may indicate the presence of previously undetected cancers in some mothers....
22 June 2015 - by Jane Fisher 
There has been much recent media interest in non-invasive prenatal testing for Down's syndrome, and this coincides with deliberations by the UK National Screening Committee on its potential inclusion in the NHS Down's syndrome screening programme...

22 September 2014 - by Siobhan Chan 
Women are confident in and value a new non-invasive prenatal test for Down syndrome that is being trialled across a number of maternity clinics in the UK, a study reports...
10 March 2014 - by Dr Victoria Burchell 
A test using a simple blood sample from the expectant mother should soon be the primary screening method for Down's syndrome, according to a report from the Royal College of Obstetricians and Gynaecologists (RCOG)...
25 November 2013 - by Dr Felicity Boardman 
I was struck by a recent article that pushed to free Down's syndrome from inappropriate, negative language - that of 'disease', of 'risk' and of 'defect'...
10 June 2013 - by James Brooks 
A test using only a blood sample taken from a pregnant woman is more reliable than current checks in indicating the likelihood of Down's syndrome, say researchers...
28 May 2013 - by David O'Rourke 
Medical genetics has changed how we think about diagnosis and treatment in almost every field of medicine. At an evening event hosted by the Royal Society of Medicine (RSM), medical genetics teamed up with obstetrics and gynaecology to explore the impact of genetics on the diagnosis of ovarian and breast cancer....

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