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Genetic screening breakthrough

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Genetic disorders could be screened for more safely through a technique that uses tiny samples of a baby’s DNA gleaned from the mother’s blood.

In a recent study, a new test used the mother’s blood while the baby was still in the womb and scanned its genetic code.

Researchers believe the new test, which is shown to work in principle, could eliminate the need for invasive and dangerous surgery such as amniocentesis.

Free-floating foetal DNA was first discovered in maternal blood in 1997, although finding it is said to be akin to trying to find a needle in a haystack because the DNA of the baby makes up only 10% of the total genetic mixture of the blood.

Scientists in China now believe they have overcome this obstacle.

Researchers led by Dr Dennis Lo, from the Chinese University of Hong Kong, tested the technique in a couple being screened for an inherited form of anaemia called beta-thalassaemia.

The complex procedure involved working out the chemical pattern sequences of almost four billion DNA molecules taken from the pregnant mother’s blood.

Next the team looked for foetal genetic signatures buried deep within the sequenced DNA.

The process was guided by genetic maps of the mother and father, which highlighted places where DNA inherited from both parents differed in the foetus.

The scientists were then able to piece together a genetic jigsaw of DNA elements from the unborn baby.

Finally, the completed foetal genetic map was scanned for key mutations. The testing showed that in this case, the baby had inherited the beta-thalassaemia genetic defect from its father and a corresponding “normal” gene from its mother. As a result, it could be seen that the unborn baby carried the disease.

In their research paper, published in the journal Science Translational Medicine, the scientists conclude: “Our study suggests the feasibility of using genome-wide scanning to diagnose foetal genetic disorders pre-natally in a non-invasive way.”

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