For years, pregnant women have had a choice of undergoing traditional blood tests or more invasive and potentially dangerous procedures to rule out the chance of any chromosomal abnormalities such as Down Syndrome that may afflict their unborn child.
The problem is that while the prenatal blood tests are safe and unlike the more invasive measures like amniocentesis and chorionic villus sampling (DVS) don’t have a risk of miscarriage, they are not that reliable. Or not reliable enough, according to executives at Natera, a San Carlos, California firm that is developing a new prenatal screening test.
“The current blood screening tests will have a false positive rate of about 5 percent,” said Jonathan Sheena, Natera’s chief technology officer. “That doesn’t sound too bad but translates to hundreds of thousands of women going through amniocentesis and [other] invasive procedures that they wouldn’t otherwise need.”
And then there is a 15 percent risk of a false negative – in other words, the results of the blood screens shows that all is well, when in fact there is a chromosomal abnormality in the fetus – Sheena said.
With invasive procedures such as amnio and CVS, the accuracy of the results are not in question, but the safety is. Sheena pointed out that one in 250 amniocentesis procedures can result in a miscarriage.
All of the above led Natera, which makes gene-based tests to help in conception and investigate causes of certain kinds of miscarriage among other products, to come up with a new test. That new DNA-based test would combine the best of the both worlds of the standard blood test and the more invasive screening procedures: It would be a safe and highly accurate test.
How is the test different from prevalent prenatal testing? The current tests look hormone level changes within the mother’s blood that are somewhat correlated to chromosomal health of the fetus, Sheena explained.
Natera, a venture backed company with the support of the likes of Sequoia Capital and Lightspeed Venture Partners, on the other hand was looking for a more reliable marker. And that is the small fragments of fetal DNA floating about in the maternal blood.
“So, what we do is we take blood draws from the mother and we look at a mixture of fetal and maternal DNA and we use our proprietary informatics to detect the chromosomal abnormalities on the five major chromosomes that are leading to birth defects,” he explained.
More specifically, the company looks at DNA SNPs (single nucleotide polymorphisms), which Sheena described as the individual nucleotides where people tend to differ.
That enables Natera to deliver results, on the chromosomes of interest in pregnancy – 13, 18, 21 [3 copies of 21 are linked to Down Syndrome], X and Y with high accuracy, he said.
Natera’s vice president of marketing and business development, Gautam Kollu, said that the company was able to make a call on 90 percent of the 166 blood samples it received, and each of those calls were made accurately. Another trial, with at least 500 samples and a more updated test using a newer version of the company’s technology, will be ready for release shortly, he added. Sheena added that other competitors who are all based in California and using DNA testing mechanisms don’t have as great an accuracy.
Kollu added that Natera’s test can be performed earlier – at nine weeks – compared to both the blood tests and the amniocentesis or CVS tests.
While extolling the accuracy of their diagnostic test, Neither Sheena nor Kollu would talk about pricing. They said that a final decision on how much it will cost has not been made.
“We can talk about cost and look at it, one way or another. Our standard of care right now in order to ascertain whether a fetus has this chromosomal abnormality is to take a big needle and stick it into the mother and hope that nothing goes wrong. That’s totally not OK.,” Kollu contended. “The ultimate value of this technology is that we won’t be unnecessarily losing babies because of unnecessary invasive procedures and I don’t know how you can put an economic value to that.”
[Photo Credit: Obstetrician checking woman from Big Stock Photo]
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