Prenatal test spots genetic anomalies linked to miscarriage
A blood test can scan a fetus’s entire genome for chromosomal abnormalities at 10 weeks of pregnancy. An extension of the non-invasive prenatal test (NIPT) for Down’s syndrome, the test could identify pregnancies that should be monitored more closely as they are at a higher risk of miscarriage or complications.
Chromosomal abnormalities occur in around 1 in 300 births. The most common are Down’s syndrome, Edwards’ syndrome and Patau syndrome, which are caused by carrying an extra copy of a chromosome – chromosome 21 in the case of Down’s. These can all be detected by the form of NIPT currently offered by private clinics in the UK, US and Australia. This test is also set to be offered by the UK National Health Service from next year.
NIPT works by detecting DNA fragments from the fetus that are circulating in the maternal blood. Now several teams around the world have developed whole-genome versions of the test that can detect rarer chromosomal anomalies, such as mosaic trisomy 22. This occurs when some cells have an extra copy of chromosome 22, and can cause learning difficulties, short stature and webbing of the neck.
Between 2000 and 2006, just over 1000 babies were born with rare chromosomal abnormalities in Europe and the UK. However, only about 50 per cent of fetuses with rare chromosomal abnormalities survive to birth, because the genetic anomalies can cause miscarriage.
Mark Pertile at Victorian Clinical Genetic Services (VCGS) in Melbourne, Australia, and his colleagues are one of the first teams to use whole-genome NIPT, and recently completed 30,000 tests of the technique. Of the 90 cases of rare chromosomal abnormalities they identified, 70 per cent were associated with serious pregnancy complications, including miscarriage.
The test was highly accurate – whenever follow-up invasive tests like amniocentesis were used, they confirmed the chromosomal abnormality that had been detected by whole-genome NIPT. Pertile’s team plan to publish detailed results from their tests of the technique soon.
The idea is that, when a rare abnormality is detected, parents can make an informed choice about how to proceed. This may include further tests, such as amniocentesis, or counselling to help them decide if they want a termination, or to prepare them for possible miscarriage or looking after a child with disabilities. “Obstetricians have told us this information is useful so they can prepare themselves and their patients,” says Pertile.
In some cases, the findings can also reduce subsequent parental guilt, says Trent Burgess at VCGS. “It’s not uncommon for people who have a miscarriage to start wondering what they did wrong – they might worry it was that one glass of wine they had,” he says. “So knowing there’s actually a genetic cause can be reassuring.”
Another form of NIPT is being developed that can detect genetic disorders like cystic fibrosis and sickle cell anaemia.
As the list of conditions that NIPT can detect increases, groups like Don’t Screen Us Out in the UK have raised concerns that the test may enable a kind of informal eugenics. Their argument is that early prenatal detection of more genetic disorders is likely to encourage additional abortions and reduce society’s tolerance of disabled people. The UK’s Nuffield Council on Bioethics has expressed concerns that NIPT could lead to sex-selective abortions, since it also allows to find out the sex of their baby as early as seven weeks into pregnancy.
But Andrew McLennan at Royal North Shore Hospital in Sydney, Australia, disagrees that such tests enable eugenics. “NIPT is not aimed at trying to make perfect humans, it simply aims to provide interested people with relevant information that allows reproductive choice.”
Whole-genome NIPT is only available at a handful of research institutes in Australia, Europe and the US, but McLennan believes it will spread. “I think moving towards whole-genome testing is a natural progression of this technology,” he says. “As long as the accuracy of the test is high, the clinical benefits could be valuable.”
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July 18, 2017 at 07:24AM