A new maternal blood test that can detect thousands of serious genetic conditions in the developing foetus could limit the need for invasive screening during pregnancy, according to scientists.
The test, to be described at the European Society for Human Genetics conference in Gothenburg on Saturday, relies on detecting tiny fragments of a foetus’s DNA that circulate in the mother’s bloodstream during pregnancy. Using advanced sequencing techniques, scientists were able to identify a very high proportion of genetic conditions, such as cystic fibrosis, that are currently only reliably diagnosed using amniocentesis or other invasive tests.
The new technique, known as non-invasive foetal sequencing (NIFS), could be used as a safer, equally accurate screening tool in all pregnancies, according to Dr Christopher Whelan, a senior computational scientist at the Broad Institute of Massachusetts Institute of Technology and Harvard University.
“This test is capable of detecting thousands of serious genetic conditions, including the majority of the conditions that appear on the major newborn sequencing and foetal anomaly panels, such as the over 2,500-gene Genomics England foetal anomalies panel,” he said.
“Examples of conditions we detected in our validation study include Noonan syndrome, Charge syndrome, Stickler syndrome, achondroplasia and dozens of other rare genetic disorders, including many where early diagnosis may change pregnancy, delivery or newborn care.”
Non-invasive blood tests based on foetal DNA have already revolutionised prenatal diagnostics, but until now have been limited to a small number of conditions, such as Down’s syndrome. The latest test, if confirmed as reliable, would expand the list to include almost all genetic conditions on the newborn screening.
“We envision this as a frontline test for cases where the foetus has presented with an anomaly in an ultrasound or another screening test,” said Whelan. “Currently, many women refuse the invasive sequencing methods – amniocentesis and chorionic villus sampling (CVS) – because of the risk to the foetus, related stress, difficulties of access, and cost, even though its diagnostic capacity is high.”
Amniocentesis involves using a thin needle to collect amniotic fluid and is typically conducted between the 15th and 20th weeks of pregnancy. It is highly accurate, but in about one in every 200 pregnancies can lead to miscarriage.
The researchers tested NIFS on 565 pregnancies at an average of 17 weeks of gestation. By sequencing the small fragments of DNA and using advanced computing methods, they were able to identify genetic variants across nearly 23,000 genes in each foetus. Checking their findings against those from either amniocentesis or CVS, they found that their test picked up 95-99% of the genetic variants found by the invasive methods and more than 97% of clinically relevant variants.
Prof Alexandre Reymond of the University of Lausanne, who was not involved in the research, said: “Sequencing the entire genome of a foetus without even getting a sample from that foetus is a tour de force. It immediately opens up treatment and prevention opportunities and means that reproductive medicine will be changed for ever.”
Prof Angus Clarke, a clinical geneticist at Cardiff University, described the work as a “very impressive technical feat” that would be especially helpful in cases where a genetic condition was suspected and where treatment of the foetus could be started prenatally.
However, using the test for exploratory screening could turn up genes of unknown significance, causing huge anxiety for parents and potentially placing babies on an unnecessary path of surveillance and medicalisation, Clarke warned. “You’re putting parents in a really difficult position,” he said. “When you don’t have a problem that you’re looking for an answer to, just coming out with potential answers can cause more problems.”
