Researchers in the US have mapped the genome of an unborn fetus, the breakthrough marks a significant advance in prenatal and genetic medicine, but also one that raises profound ethical issues. As a result, researchers at the University of Washington say they will be able to screen a foetus that is only eight weeks old for thousands of genetic disorders with an accuracy of 98 per cent.
Currently, the common procedure for pregnant women who want to check their baby for genetic, chromosomal abnormalities is Amniotic Fluid Test – AFT – or Amniocentesis, it’s a risky procedure in which a small amount of amniotic fluid, which contains foetal tissue is sampled – via a very large needle – from the amnionic sac surrounding the fetus.
Researchers were able to map the genomes of two fetus’ via non-invasive maternal blood and paternal saliva samples taken from two pregnant women halfway into their second trimester at 18 weeks gestation. The samples contained enough information to accurately interpret the babies DNA ::::
Researcher Jacob Kitzman says in addition to sequencing those pieces of DNA, researchers were able to sequence each of the parents to pull together the genome sequence of the child.
“We think it’s a huge improvement. Many genetic screens that are done today require an invasive procedure,” Kitzman said. “If you think of the genome as a book with multiple chapters, those current tests can detect if an entire chapter is missing or if there’s an extra copy of an entire chapter. But what we’ve shown is that this can go down to the level of looking for a single typo.”
Scientists have long known that a pregnant woman’s blood plasma contains cell-free DNA from her developing fetus. Fetal 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 fetus.
Based on this phenomenon, other research labs are designing maternal blood tests for major aberrations in the fetus’s 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 congenital abnormalities. For example, a test targeted for Down syndrome would look for evidence of three copies of chromosome 21.
There are more than 3,000 single gene disorders which this method may be able to detect, one day. Kitzman says proving it is possible to detect the multitude of gene disorders is the next step.
“If one had the full genome sequence of an unborn foetus, these disorders could be diagnosed comprehensively,” Kitzman said. “In the studies we had two families where the baby was born and apparently healthy. So this would need to be refined and replicated and shown that it can actually detect a disease. But in principle, as with other genome sequences approaches, this would be very much useful for that purpose.”
The University of Washington research is published in the journal Science Translational Medicine.
source: medical x press