Genetic Screening During Pregnancy Shows Promise

According to a study published inScience Translational Medicine, researchers at the University of Washington have successfully reconstructed the whole genome sequence of a human fetus by analyzing blood samples from the mother and saliva samples from the father.

The researchers findings open up the possibility of assessing a fetus non-invasively for all single-gene disorders.

Approximately 1% of newborns are born with disorders that are caused by a defect in a single gene. These "Mendelian" disorders include cystic fibrosis, Huntington's disease, and Tay-Sachs disease.

In the future, the new non-invasive technique could help screen for these types of genetic mutations in the fetus without increasing the risk of miscarriage, said Jay Shendure and his team at the University of Washington.

Shendure explained: "This work opens up the possibility that we will be able to scan the whole genome of the fetus for more than 3,000 single-gene disorders through a single, non-invasive test."

At 18.5 weeks gestation, the researchers were able to map the whole genome of a fetus and then reconstructed it using DNA from the mother's blood plasma and saliva from the father.

Although fetal DNA is found in the mother's blood plasma, it can be challenging to distinguish which genetic signature belongs to the fetus and which belongs to the mother. As a result the team used a new technique in order to identify blocks of haplotypes (genetic variation), that could be traced back to the mother's genome.

The researchers were then able to use this information, together with data from the father's saliva sample, to determine which genomes the fetus inherited. The team then conducted a more intensive examination of the mother's DNA sample in order to identify new genetic variations that appeared only in the fetal genome.

To test the accuracy of their genetic predictions, the team collected blood from the baby's umbilical cord at birth and found that they had identified 39 of the baby's 44 new mutations during the genome reconstruction.

The techniques used by the team were able to evaluate many and more subtle variations in the fetus' genome, down to tiny, "one-letter" changes in the DNA code, said Jacob Kitzman, a graduate student in Shendure's lab.

Kitzman explained: "The improved resolution is like going from being able to see that two books are stuck together, to being able to notice one world misspelled on a page."

Written By Grace Rattue

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