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Not Yet Perfection

As non-invasive prenatal tests for genetic abnormalities are adopted in the clinic, the Wall Street Journal says that there may be confusion among doctors and patients regarding what the results of those tests mean. In fact, the Journal points out, the American College of Genetics and Genomics is working on a statement urging such tests to be called "screens" to emphasize that they predict risk rather than give definitive results. Four US companies, Ariosa Diagnostics, Natera, Sequenom, and Verinata Health, which is part of llumina, offer such tests.

Non-invasive screens appeal to many pregnant women as they avoid the small miscarriage risk associated with amniocentesis. Jeff Chapa, the head of obstetrics and maternal-fetal medicine at the Cleveland Clinic, tells the Journal that doctors there perform half as many invasive tests.

"All patients want to hear that you don't need to have something invasive," says Laura Limone, genetic-counseling supervisor New Jersey Perinatal Associates in Livingston and a member of Sequenom's speakers bureau. "Those who understand the technology find it very promising, but we also know it isn't perfect yet."

Indeed, the screens can yield false-positive or false-negative results, and positive results should be followed up on with invasive procedures, the Journal says. Athena Cherry, who heads the cytogenetics lab at Stanford University Medical Center, tells the Journal that case studies like one of a patient who terminated a pregnancy after only the screening — and the fetus was subsequently found to be normal — indicate that the message to follow up on positive results may not be "driven home enough."

False-negative results also may occur, as one instance was recounted at the ACMG annual meeting last month, as our sister publication GenomeWeb Daily News reported. The test, from Verinata, indicated that the fetus did not have Down syndrome but an amniocentesis performed after unusual ultrasound findings found that the fetus did have Down syndrome — the company's test had boasted a 100 percent sensitivity for detecting the syndrome; it now indicates a sensitivity greater than 99.9 percent, the Journal adds.

"Noninvasive prenatal [testing] as a whole has the potential to someday replace invasive procedures," says Jonathan Sheena, Natera's chief technology, adding that "the field has taken a giant leap forward … but we believe it is important to understand they don't replace invasive tests yet."