Current screening strategies for Down syndrome, caused by fetaltrisomy 21 (T21), and Edwards syndrome, caused by fetal trisomy 18(T18), have false positive rates of 2 to 3%, and false negativerates of 5% or higher. Positive screening results must be confirmedby amniocentesis or chorionic villus sampling, which carry a fetal loss rate ofapproximately 1 in 300 procedures. Now an international,multicenter cohort study finds that a genetic test to screen fortrisomy 21 or 18 from a maternal blood sample is almost 100%accurate. The results of the study are published online in the American Journal of Obstetrics and Gynecology. The trial evaluated a novel assay known as Digital Analysis ofSelected Regions (DANSR) that analyzes fetal cell-free DNA, smallDNA fragments which circulate in maternal blood. Unlike similartests that analyze DNA from the entire genome, DANSR analyzes onlythe chromosomes under investigation for a more efficient and lessexpensive process. The results are evaluated with a novel analysisalgorithm, the Fetal-fraction Optimized Risk of Trisomy Evaluation(FORTE), which considers age-related risks and the percentage offetal DNA in the sample to provide an individualized risk score fortrisomy detection. A total of 4,002 pregnant women from the United States, theNetherlands, and Sweden were enrolled in the NICE (Non-InvasiveChromosomal Evaluation) study. The mean maternal age was 34.3 yearsand the cohort was racially and ethnically diverse. Blood sampleswere taken before the women underwent invasive testing for anyindication, and 774 samples were excluded prior to analysis. Of the3,228 samples that underwent analysis, 57 cases were excluded dueto low fetal cfDNA in the sample and 91 samples were excluded dueto failure of the assay. The classification of samples as High Riskor Low Risk using the DANSR and FORTE method was compared with theresults from amniocentesis and CVS. The DANSR and FORTE method identified 100% of the 81 T21 cases asHigh Risk, and there was one false positive among the 2,888 normalcases, for a false-positive rate of 0.03%. Of the 38 T18 cases, 37were classified as High Risk and there were 2 false positives amongthe 2,888 normal cases, for a sensitivity of 97.4% and a falsepositive rate of 0.07%. Prior studies of cfDNA have been case-control studies, comparingdetection in subjects identified with T21 or T18, to a selectedgroup of those with normal karyotypes. The current study included alarge cohort of subjects undergoing invasive prenatal diagnosis.This allowed the researchers to assess the potential impact ofother complex and unusual abnormalities on cfDNA test results.Overall, the presence of other chromosomal variants did notinterfere with the detection of T21 or T18. While the studyincluded primarily high-risk women, all women undergoing invasiveprenatal diagnosis for any indication were eligible, so the cohortrepresents a broader population than reported in previous studies. "The improvement in sequencing efficiency achieved by the DANSRplatform provides a more affordable, scalable approach to cfDNAanalysis with high throughput and potential for widespread clinicalutility," says lead investigator Mary E. Norton, MD, director ofperinatal research, Lucile Packard Children's Hospital at StanfordUniversity. "Cell-free DNA offers high accuracy with a single bloodtest. It is potentially suitable as a replacement for current,relatively inefficient aneuploidy screening." Additional References Citations. We are high quality suppliers, our products such as Floating Desktop Globe , Magnetic Rotating Globe Manufacturer for oversee buyer. To know more, please visits Magnetic Floating Globe.
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