Scientists in Britain have announced that they have developed a prenatal DNA test for Down syndrome, which is safer and more effective than what is used today.
The new genetic test (reflex DNA screening), which is less stressful for mothers, takes place around the 11th week of pregnancy and provides fewer false positive results than the existing test.
It can also be used to diagnose two other serious but rarer chromosomal disorders (trisomies), Edwards and Pataw syndromes, caused by the presence of an extra chromosome in fetal cells.
Researchers at the Queen Mary University’s Institute for Preventive Medicine in London, led by Professor Sir Nicholas Wald, published in the journal Genetics in Medicine, tested the test in five obstetric clinics in more than 22 women.
Of these, 11% did the new DNA test. The new test was found to have a 95% diagnostic accuracy in detecting the three chromosomal disorders, compared to 81% of the existing test. The percentage of false-positive results of the new test was only 0.02% or two cases per thousand, compared to 2.42% of the existing test (false-positive results deceive that there is a disease, without it actually happening).
Today, the diagnosis of Down syndrome and the other two chromosomal disorders is made with a combination of blood test and ultrasound examination between the tenth and 14th week of pregnancy. If – taking into account the age of the mother – it is estimated that there is an increased risk to the baby (over a probability of 150), an invasive amniocentesis or trophoblast test is performed to confirm.
The new test in the first phase uses the same combination of blood and ultrasound tests. If the risk is estimated to be more than one in 800, then the pregnant woman’s own blood is sent for DNA analysis.
The British National Health Service, according to the Guardian, intends to introduce the new test from 2018 for those women who are considered at high risk for any of the three chromosomal diseases (also known as trisomies 21, 18, and 13) . Dr Wald said the new test could be adopted by hospitals around the world in the future, as long as they have laboratories that do DNA analysis.