US researchers develop new Down syndrome test

WASHINGTON - A prenatal blood test can be used to determine if an unborn baby has Down syndrome without the small risk to the fetus posed by invasive testing methods such as amniocentesis, US researchers said yesterday.

Researchers led by Stephen Quake of Stanford University created a way to look for the extra chromosomes that cause the condition and similar birth defects 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 inserted into the uterus, and can be done earlier in a pregnancy.

Down syndrome, which causes mental retardation and other problems, is caused when a child has three copies instead of 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 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," Quake said by telephone.

Blood tests for pregnant women like the alpha-fetoprotein test can find potential signs of a chromosomal disorder such as Down syndrome, but cannot diagnose it with certainty.

Quake said such tests serve as only "indirect and weak predictors of what's going on."