Getting fetus’ genetic makeup from a blood test

Scientists have announced that a simple blood test, rather than more invasive tests such as amniocentesis, can determine a fetus’s genetic make-up, identifying mutations causing any of about 3,000 inherited disorders that arise from a glitch in a single gene, such as cystic fibrosis.

This  procedure  can be done without knowing who the father is, much less obtaining a sample of his DNA. The father-free method promises to make fetal DNA sequencing possible in every pregnancy, if hurdles including cost and accuracy are overcome.

 “You’ll be able to detect any kind of abnormality early, quickly, without distress and safely. This is the way of the future.”

Determining a fetus’s genome might give women more reasons to end a pregnancy. But it would also let physicians identify conditions that can be treated before birth or immediately after. “The way it’s done now, parents wait until a newborn gets sick and suffers in the first weeks of life, and only then does the doctor start figuring out the baby has a metabolic or immune disorder.”

With prenatal genetic testing, in contrast, the parents would know by the end of the first trimester (12 to 13 weeks) if the fetus has a genetic or chromosomal defect. That way, they can be ready if the baby has special needs, which can be as simple as a certain diet.

DNA IN THE BLOOD

The new study is based on the fact that a pregnant woman’s blood contains millions of DNA fragments. Most are from her own cells. But early in pregnancy, 5 to 10% are from her fetus. Unfortunately, it’s not possible to tell directly which is the mother’s DNA and which is the baby’s.

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 Using sequencing machines from Illumina, they deduced the fetal genome sequence by counting the relative proportions of different DNA variants, knowing that the most common ones had to be mom’s because the mix of DNA contained her own as well as that the fetus inherited from her.

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