Noninvasive Method For Evaluating Down Syndrome Risk Discovered
Scientists at Aria Diagnostics in San Jose, have discovered a new method to detect chromosomal abnormalities . The recent statistical algorithm, DANSR/FORTE assay, can detect 21 and 18 trisomy using a noninvasive test performed on maternal blood. Unlike other genetic screening tests, this assay is more scalable and has the benefit of reducing the number of unnecessary amniocenteses.
Children born with trisomy 18 or trisomy 21 have different physical traits and a certain degree of mental handicap. Even if it can not be treated, children with Down syndrome can lead normal lives if the necessary care benefits are provided.
Aneuploidy or fetal chromosomal abnormalities can be diagnosed with invasive tests such as amniocentesis or chorionic villi sampling. Although accurate, these tests are expensive and, moreover, could induce miscarriage. Another technique, MPSS, massively parallel shotgun sequencing, examines cells without DNA from maternal plasma to detect trisomy 21, or Down syndrome, and trisomy 18, or Edwards syndrome. Even if it can accurately identify these abnormalities, one of the main shortcomings of MPSS is that it requires a lot of DNA sequencing.
Researchers at the Diagnostics area in San Jose, CA have developed a new test that searches only for certain chromosomes. That means it needs 10 times less DNA than MPSS.
With thys study, which will be published in the April issue of the American Journal of Obstetrics & Gynecology (AJOG), researchers have developed a new statistical algorithm, the fetal-fraction Optimized Risk of Trisomy Evaluation (FORTE â¢), which correlates maternal age with the percentage of fetal DNA in the sample, thus obtaining a certain score for trisomy. Dr.Ken Song, MD, explains the idea of this algorithm. “The higher the fraction of fetal cfDNA, the greater the difference in the number of cfDNA fragments originating from trisomic versus disomic [normal] chromosomes and hence the easier it is to detect trisomy.’
To test the accuracy DANSR / STRONG assay, Dr. Song and his colleagues examined a sample of 123 normal pregnancies, 36 of T21 and 8 of T18. All cases were tested using DANSR / STRONG assay for detection of trisomy 18 and trisomy 21. The new testing method was accurate in all 36 cases of T21 and 8 cases of T18.
Kypros H. Nicolaides, MD, senior author of the University of London study draws attention to the fact that all cases tested so far were suspected to have a chromosomal abnormality. He added that it would be necessary to verify the accuracy of cfADN testing on the general population, where the risk of aneuploidy is much smaller.