Down Syndrome :: Blood test for Down’s syndrome developed

Ravgen publishes study in the Lancet describing a non-invasive test for prenatal diagnosis based on fetal DNA in maternal blood.

Ravgen, a privately held company dedicated to revolutionizing diagnosis and treatment of human diseases through innovative new technologies, announced today the publication of a study using genetic markers on fetal DNA recovered from maternal blood as the basis for a non-invasive prenatal test. The study being published in early release online in the medical journal The Lancet, by Dhallan et al, relied on common genetic variants in the human genome called single nucleotide polymorphisms (SNPs) to determine potential chromosomal abnormalities in the fetuses.

According to the National Center for Health Statistics, there has been a steady increase in pregnancies in women over age 35. Since advanced maternal age is a risk factor for genetic abnormalities, prenatal testing will be necessary for more and more women. Also, in a recent bulletin, the American College of Obstetricians and Gynecologists (ACOG) recommended that all women, irrespective of maternal age, be offered genetic screening.

It has long been known that some fetal cells circulate in the maternal blood during pregnancy so research has focused on trying to develop a blood- based prenatal test. However, such tests have remained elusive given the difficulty in separating the small number of fetal cells from the maternal blood. Ravgen scientists have perfected the ability to detect fetal DNA from an easily obtained maternal blood sample. With the availability of human genome sequence data, which provides enhanced understanding of genetic variations such as SNPs, Ravgen scientists are making significant advances toward a DNA-based, non-invasive prenatal test.

The results of the study showed that the Ravgen methods enabled the direct detection of fetal DNA in the mixture of maternal and fetal DNA, which is normally present in the maternal bloodstream during pregnancy (the average percentage of fetal DNA identified was 34.0%). Genetic abnormalities can be identified by measuring the number of copies of SNPs on different chromosomes. Of the 60 samples analyzed, Ravgen scientists identified three trisomy 21 samples, and 57 with a normal copy number of chromosomes 13 and 21. By comparing these results to amniocentesis or newborn reports from the clinical sites, it was shown that Ravgen scientists were correct in two of the three trisomy 21 cases and were correct in 56 of the 57 normal cases (one sample was a false negative and one sample a false positive).

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