May 27, 2012

Bay State likely to see new test for Down syndrome

A fetal DNA test that could replace invasive screening may be offered to pregnant women in Worcester County.

The Associated Press

WORCESTER, Mass. - A simple blood test done on maternal serum early in the first trimester of pregnancy to determine if a baby has Down syndrome or more severe genetic disorders will likely be offered to pregnant women in Worcester County later this year.

The test, which analyzes fetal DNA in the mother's blood, underwent a clinical trial last year at the University of Massachusetts Medical School, with the research study published this month in Obstetrics & Gynecology.

It went on the market a few months ago under the name Verifi, made by California-based Verinata Health, and can detect with nearly complete accuracy the three most common genetic syndromes in infants: Down syndrome (Trisomy 21), Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome).

It can also detect Turner syndrome, a treatable condition in which girl babies are missing all or part of the X chromosome and face various health problems, including infertility.

The disorders are usually not inherited, but are the result of random events during early cell division.

Most importantly, the test could replace older prenatal blood screening that is unreliable at predicting Down syndrome and other chromosomal abnormalities -- there are a lot of false positives -- and often require further invasive tests such as amniocentesis, which carry a small risk of miscarriage.

The Verifi genomic test, first developed at Stanford University, uses fast gene sequencing instruments combined with algorithms to analyze the mother's blood using a cell-free method that looks at DNA left over in blood samples in which cells have died. About 20 percent to 25 percent of the DNA is from the fetus, which gives analyzers much more DNA to work with.

Previous tests looked for a few fetal blood cells, perhaps 10 out of 200 billion in the sample, and those were fragile.

Dr. Tiffany A. Moore Simas, assistant professor and director of obstetrical and gynecological research at the medical school and a gynecologist and obstetrician at the UMass Memorial Medical Center, is a researcher who led the study at the medical school.

The upcoming availability of the new test, which she said will likely be offered to expectant mothers this fall or winter, will give women more choices.

It should also make the current plethora of tests less confusing.

"It has potential to change things," she said.

The traditional alpha-fetoprotein maternal blood test now routinely used is first checked at 11 to 13 weeks of pregnancy. If alpha-fetoprotein levels are elevated, an ultrasound is done (to rule out multiple fetuses and check for anatomical abnormalities).

This is followed by another blood test after 16 weeks and possible amniocentesis or chorionic villus sampling, another invasive procedure with a risk of miscarriage.

There are various components of the test, which can check for open neural tube defects such as spina bifida as well as Down syndrome and Trisomy 18.

"With those (traditional) blood tests, they never come back with a result of completely risk-free," Moore Simas said.

"They are always followed with discussion on age, risk, an ultrasound and genetic counseling. The process as it exists now is confusing. There is no very succinct way to explain options -- and one of those options may be no testing at all."

Moore Simas is listed as an author in the study, which took place from August 2010 to July 2011.

UMass Medical School was one of 60 testing sites in the U.S. Blood samples were collected from a total of 2,882 women in their first and second trimesters who were considered high-risk pregnancies and who underwent diagnostic procedures such as amniocentesis. Moore Simas said they were asked to be in the study, which required getting a vial of blood drawn from the arm. The cell-free DNA genomic tests results were then compared with amniocentesis results, considered the gold standard.

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