Today's NYT describes a new strategy for Down Syndrome screening. The new test, developed by a company called Sequenom, screens the mother's blood sample for fragments of RNA produced from fetal chromosomes.
Dr. Lo looked for genes on Chromosome 21 that were active in the fetus but not in the mother. That means that any such RNA found in the mother's bloodstream comes from the fetus. The Sequenom test then looks at spots where the version of those genes inherited by the fetus from the father might differ from the version inherited from the mother. If the baby has the normal two copies of Chromosome 21, the amount of RNA from the mother's version and the father's version should be the same. If the baby has an extra copy of the chromosome, one version would be twice as abundant as the other.
Although it's still in trials, Sequenom's test might eventually be used as early as ten weeks into the pregnancy. But its real promise lies in the potential to eventually replace amniocentesis and chorionic villus sampling (CVS), invasive tests which carry a small but significant risk of miscarriage. This would be a huge relief for pregnant women who have ambiguous results on preliminary tests. Such a woman must currently accept the risk of miscarriage from the invasive tests, or spend the entire pregnancy uncertain whether her child has Down syndrome. One of my friends had to make that choice a few years ago (she chose not to have amnio), and although she handled it gracefully, I was shocked that medicine hasn't yet come up with a better way.
It looks like there will be a better way soon - Sequenom isn't the only group working on the problem. Another maternal blood test, which identifies extra copies of chromosome 21 by shotgun sequencing fetal DNA in the mother's blood, has been developed by researchers at Stanford and is described in a PNAS paper published today. The study is preliminary - it only involved 18 women - but it serves as proof of concept.
According to a webmd article, the lead author of the Stanford study, Stephen Quake, had personal motivation to develop a noninvasive test: his wife underwent amniocentesis and then CVS during her first two pregnancies: "It was nerve-wracking for all of us, and I can only imagine how the fetus felt." (source).
I am unsurprised, but disappointed, to see that team "ignorance is good; because it keeps you from doing what we don't want you to" managed to worm their way into the story. They can think that aborting downs fetuses is wicked and wrong if they must; but opposition to a medical technique that reduces invasiveness and risk of miscarriage seems a bit much. Probably spend the rest of their time whining about how people wouldn't need HPV vaccines if they weren't so loose.
You know, when I first read the story, I missed that part entirely. I'd like to say it wasn't there in the original story - but probably I just saw "Sarah Palin" and my eyes glazed over. Anyway, as far as I'm concerned, accurate information beats ignorance or partial, possibly misleading information every time.