A prenatal test that analyzes a mother’s blood and father’s saliva may one day be all it takes to check a fetus for genetic illnesses, replacing one that requires drawing fluid from the uterus, a study suggests.
Scientists have sequenced the DNA of a fetus at 18 weeks of pregnancy using the technique. Their analysis found 39 of the baby’s 44 brand-new mutations, not shared with either parent, according to the study published today in Science Translational Medicine.
Scientists compared their method with a traditional gene sequence from the umbilical cord once the baby was born and found the experimental method was 98 percent accurate. The results may point to a new way to scan a fetus’s genome for mutations that can cause illness, such as Huntington’s disease and Down syndrome, without inserting a needle into a pregnant woman’s uterus to draw amniotic fluid, the current practice.
“Part of what this study does is expand thinking about how genomics can be relevant,” said Jay Shendure, one of the study authors and an associate professor of genome sciences at the University of Washington in Seattle, in a telephone interview. “The main advantage is that it’s not invasive.”
The current testing method, called amniocentesis, carries a risk of miscarriage. Even with no additional risk, though, most women probably would want a less-invasive test, Shendure said.
About 10 percent of cell-free DNA in a pregnant woman’s blood comes from her fetus, Shendure said. He and fellow researchers compared groups of the mother’s genes that reside on the same chromosome. Using these groupings, the researchers were able to pick out which genes were new to the baby.
To determine what role the father played, the researchers used DNA from a saliva sample. Anything that wasn’t the same as the mother’s was compared to the father’s.
“The fetal plasma DNA is contaminated with mom’s DNA, so any time we see a variant that corresponds to something from dad, we can infer that was transmitted,” he said.
Additionally, his group was able to find so-called de novo mutations, which didn’t occur in either parent. Those gene variants are important because they underlie a number of illnesses where only one variant is required to sicken a person.
Shendure’s group showed that the idea was possible, and he expects cheaper, better sequencing will be available in the future, he said. The project was funded by the National Human Genome Research Institute and the Washington Research Foundation.