I didn’t build in quite enough buffer time to get started on my next reader-initiated travel blog (it’s a secret – I’m not telling until I get there). I’m going to shoot out of the door in this next break. There may be a cat picture for my 3:30pm post. Just to warn you.
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We haven’t had any science yet. How about this cool story?
Invasive fetal (or prenatal) testing is serious business. Chorionic villus testing and amniocentesis can be used to help detect chromosomal abnormalities or disorders, but there is a small but noted risk of miscarriage with these procedures. On June 6th the Los Angeles Times reported on research being performed that would allow much less risky sequencing of fetal DNA:
To set about their task, Shendure’s team started by sequencing the genome of an anonymous pregnant woman, using a complete sample of her DNA obtained from her blood cells. They also sequenced free-floating DNA fragments extracted from her blood plasma, repeating their work until they had decoded every part of the human genome 80 times.
That plasma contained a mix of 10% fetal DNA and 90% maternal DNA, all in tiny fragments. The scientists needed to be able to tell which pieces were from the mother and which belonged to the fetus.
To solve that problem, the scientists relied on the fact that genetic material is inherited in long strands of DNA, called chromosomes — and that tiny genetic variations on the same chromosome are usually inherited together, in blocks known as haplotypes. If a given haplotype was present in the fetus as well as in the mother, it would be detected in the plasma in extra amounts.
The scientists also sequenced the father’s DNA, which was extracted from saliva. This allowed the team to figure out whether genetic variations in the fetus that didn’t match the mother were inherited from the father or were new mutations. On average, about 50 new mutations show up in a fetus.
The scientists checked their results against a blood sample taken from the baby’s umbilical cord after birth. Their calculations were more than 98% correct, they found, and they had detected 39 out of the 44 new mutations. None of those mutations had known medical consequences, the researchers said.
This approach could be used to devise a single test to screen for the 3,000 known disorders that are caused by mistakes in single genes. Individually, they are rare, but together they affect about 1% of births.