Using a novel non-invasive technique, scientists for the first time have successfully sequenced the genome of a foetus without tapping its protective fluid sac. Maternal blood sampled at about 18 weeks into the pregnancy and a paternal saliva specimen had enough information for the scientists to map the foetus’ DNA.
This method was later repeated for another expectant couple closer to the start of pregnancy. The researchers checked the accuracy of their genetic predictions using umbilical cord blood collected at birth, the journal Science Translational Medicine reports. Jacob Kitzman and Matthew Snyder, working in the lab of Jay Shendure, associate professor of genome sciences at the University of Washington, US, led the study. Scientists have long known that a pregnant woman’s blood plasma contains cell-free DNA from her developing foetus, according to a Washington statement.
Foetal DNA appears in the mother’s plasma a few weeks after conception. It rises during gestation and normally vanishes after the baby arrives. While the concentration varies among individuals, about 10 percent of the cell-free DNA in a pregnant woman’s blood plasma comes from her foetus. Based on this phenomenon, other research labs are designing maternal blood tests for major aberrations in the foetus’ genetic makeup. The tests are considered a safer substitute for the more invasive sampling of fluid from the uterus, a common procedure in obstetrical practice.
These new tests search for just a few genetic disorders or specific birth abnormalities. For example, a test targeted for Down Syndrome would look for evidence of three copies of chromosome 21. Kitzman explained what distinguishes his team’s latest methods is the ability to assess many and more subtle variations in the foetus’ genome, down to a minute, one-letter change in the DNA code. ”The improved resolution is like going from being able to see that two books are stuck together to being able to notice one word misspelled on a page,” said Kitzman.