A new study has brought the step of sequencing foetal genome from the mother's DNA one step closer.
The discovery may offer prospective parents a non-invasive way of testing for any congenital disease.
Scientists in Hong Kong and the United States have mapped hundreds of thousands of DNA code variations spread across the genome of an unborn child in order to determine whether or not it would inherit a rare blood disorder.
The same approach could indicate, months before an infant is born, whether he or she has inherited cystic fibrosis, sickle cell anaemia and other diseases. It could also determine a child's complete genome sequence before birth.
"We're about a factor of 100 away from commercial capability, but that will change," Nature quoted Charles Cantor chief scientific advisor at the genetic testing firm Sequenom, based in San Diego, California, as saying.
Building on the discovery that fragments of foetal DNA are present in a mother's plasma, the company and other scientists are working to develop prenatal DNA tests as an alternative to amniocentesis and other invasive ways of collecting DNA from a developing foetus that raise the risk of miscarriage.
It was easy to see that the father's mutation appeared in the mother's blood, indicating that the foetus had inherited its father's faulty allele.
Dennis Lo, a chemical pathologist at the Chinese University of Hong Kong, and his team developed a way to count how many times each of the mother's healthy and mutated alleles appeared in the blood sample. They found more of the healthy allele, suggesting that the foetus had inherited the correct maternal copy of the gene and would not develop beta-thalassaemia.
Lo's team ended up sequencing 94 percent of the foetal DNA. But because the foetus's sequences were inferred from their parents' gene scans, whole-genome sequences of the parents (rather than a comparison with 900,000 points) are needed to get a complete foetal genome, Lo says.
"I do believe it's possible to sequence most of the foetal genome from maternal blood," agreed Steve Quake, a bioengineer at Stanford University in California.
The work is published online today in Science Translational Medicine.