WASHINGTON Oct 6 A prenatal blood test can be
used to determine if an unborn baby has Down's syndrome without
the small risk to the fetus posed by invasive testing methods
such as amniocentesis, U.S. researchers said on Monday.
Researchers led by Stephen Quake of Stanford University in
California created a way to look for the extra chromosomes that
cause Down's and similar birth detects in the tiny amounts of
fetal DNA that circulate in the mother's blood.
The test, which requires a small blood sample from the
mother, is safer than amniocentesis, in which a needle is stuck
into the uterus, and can be done earlier in a pregnancy.
Down's syndrome, which causes mental retardation and other
problems, is caused when a child has three copies instead of
the normal two of chromosome 21.
The test also detects other chromosomal conditions such as
Edward syndrome, which kills half of babies in the first week
of life and Patau syndrome, which kills more than 80 percent of
children in infancy.
Quake's team demonstrated the accuracy of the new genetic
test in a small study involving 18 women.
It accurately identified the nine women with a Down's
syndrome pregnancy and three others with fetuses with different
chromosomal disorders, the researchers wrote in the journal
Proceedings of the National Academy of Sciences.
"It's the first universal, noninvasive test for Down
syndrome. So this should be the first step in putting an end to
invasive testing procedures like amniocentesis and chorionic
villus sampling," Quake said in a telephone interview.
Blood tests for pregnant women like the alpha-fetoprotein
test can find potential signs of a chromosomal disorder such as
Down's, but cannot diagnose it with certainty.
Quake said such tests serve as only "indirect and weak
predictors of what's going on."
For a definitive determination, women must have an invasive
diagnostic procedure such as amniocentesis or chorionic villus
sampling. This is done typically after the 15th week of
These procedures carry a small risk -- roughly 1 percent --
of causing a miscarriage or birth defects.
Because of that, their routine use has been mostly by women
age 35 and older at higher risk for having Down's syndrome
babies. Scientists have been working for years to devise safer,
noninvasive tests suitable for any pregnant woman.
Quake said the new test also could be administered much
earlier in a pregnancy than amniocentesis or CVS -- potentially
as early as five weeks after conception. And the results are
back within a couple of days, instead of two to three weeks.
Some women terminate the pregnancy when they learn the
fetus has Down's syndrome but others, including Republican U.S.
vice presidential candidate Sarah Palin, do not.
Quake said the new test could be widely available in two or
three years, and could become a routine prenatal test of a
baby's health. Quake said the next step is a larger study
involving hundreds of women.
Stanford University has filed a patent on the test and two
companies are negotiating for the licensing rights, Quake said.
He said he is has been hired as a consultant for both
companies, which he declined to identify.
San Diego-based Sequenom Inc SQNM.O is also working on a
Down's syndrome blood test using a different approach.
(Editing by Maggie Fox and Eric Walsh)