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Fetal genome sequenced using only a blood sample from the mother

9 July 2012
Appeared in BioNews 664

US researchers have for the first time sequenced the genome of a fetus using only a blood sample from the mother. It is hoped this new form of non-invasive sampling could allow doctors to screen for a range of genetic conditions prenatally, with minimal risk to the fetus.

'We are interested in identifying conditions that can be treated before birth, or immediately after. Without such diagnoses, newborns with treatable metabolic or immune system disorders suffer until their symptoms become noticeable and the causes are determined', said Professor Stephen Quake of Stanford University, California, who led the study.

The prenatal detection of genetic conditions allows for treatments to begin immediately after birth. However, current methods for detection, such as CVS and amniocentesis, require invasive procedures that can endanger the pregnancy.

New research demonstrates how non-invasive procedures involving blood samples can avoid these risks. As a mother's blood is known to contain both maternal and fetal DNA, samples can be used to identify genetic conditions prenatally. Non-invasive tests for some chromosomal abnormalities, such as Down's syndrome, are currently available and research published last month demonstrated that a fetus' genome could be sequenced using blood samples taken from both the mother and father, allowing doctors to screen for other genetic conditions.

This latest advance, however, negates the need for a paternal DNA sample, allowing the entire genome of the fetus to be sequenced, even in cases where the paternity is unknown or the father is not available to provide a DNA sample.

As fetal DNA contains DNA from both the mother and father, the new study demonstrates how paternal sequences can be inferred from the maternal blood sample. The researchers were able to sequence the entire fetal genome with 99.8 percent accuracy.

A potentially cheaper procedure was also developed, whereby only the fetal exome was sequenced (the portion of the fetal genome that codes for proteins). Over the course of pregnancy increasing amounts of fetal DNA pass across the placenta and into the mother's bloodstream, such that by the final trimester researchers were able to successfully sequence 90 percent of the fetal exome.

The authors of the study state that the techniques developed offer 'a gateway to comprehensive non-invasive prenatal diagnosis of genetic disease', which would be of particular significance to those diseases where patients would benefit from immediate postnatal treatment, such as severe immunodeficiency. Further research and development is required before the techniques can be trialled in clinics, however.

The study was published in the journal Nature.

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