Mom s blood holds clues to fetal genetics

In October, we discussed the first test to analyze an expectant mother's blood early in pregnancy to detect Down syndrome. This was a boon, since older, invasive tests, such as the conventional methods of amniocentesis or chorionic villus sampling, carry a slight risk of premature labor or miscarriage. Now, another variety of prenatal blood test, called DANSR ¢ (Digital Analysis of Selected Regions), has been developed; used in tandem with the novel FORTE (Fetal-fraction Optimized Risk of Trisomy) alogrithm, it has been shown to improve upon the accuracy of the blood tests currently available. Two evaluations of this new method have just been published in the American Journal of Obstetrics and Gynecology, and the findings are promising.

DANSR ¢ was developed by a team of scientists at Aria Diagnostics in San Jose, Calif.; the test is a more efficient and thus less expensive means of determining whether the genome contains three copies of chromosome 21, which indicates Down syndrome, or three copies of chromosome 18, known as Edwards syndrome. The Aria scientists use the blood test in tandem with the FORTE algorithm, which takes into consideration the age-related risks of the mother and the amount of fetal DNA in the sample to generate an individualized risk score for both genetic disorders.

When Aria scientists tested the combined performances of the prenatal blood test and algorithm on 123 normal pregnancies, as well as 44 Down or Edwards syndrome pregnancies, they were able to correctly identify all of the pregnancies with either syndrome with a greater than 99 percent predictive accuracy.

While these results, as ACSH s Dr. Gilbert Ross observes, are promising, it remains to be seen whether the novel screening method will be as accurate in the general population, given that the maternal blood samples analyzed in these studies were obtained from high-risk pregnancies. Furthermore, if the method were to become a commonly used screening tool, the cost would need to be comparable to that of current available methods.

As we noted in our earlier coverage, knowing whether a child will have a major chromosomal abnormality allows parents to better prepare themselves for the challenges and special needs they may face. With about 83,000 children in the U.S. living with Down syndrome in 2002 and even more now, given that the frequency of Down syndrome births has been steadily increasing having a safe and highly effective test available would be important for many families.