New method to detect fetal Down syndrome through maternal blood

Researchers from Cyprus Institute of Neurology and Genetics, Mitera Hospital, Greece; Kapodistrian Athens Hospital and the British Institute of the Wellcome Trust Sanger have just announced a successful trial of a blood test for early diagnosis of Down syndrome. Accordingly, pregnant women will be analyzed for blood to detect DNA differences between mother and fetus, thereby correctly diagnosing which fetus has Down syndrome.

Down syndrome is a major genetic cause of mental retardation, with a proportion of 1/700 children born worldwide. It happens when a child has 3 copies of chromosome 21 instead of 2 as usual or 3 corresponding chromosomes 21.

The risk of a baby with Down syndrome will increase when the mother is older. The risk of a baby with Down syndrome in a 40-year-old mother is 16 times higher than a 25-year-old mother.

Currently, pregnant women undergo a series of fetal diagnoses including ultrasound and many blood tests. For example, a method of testing protein levels is called PAPP-A in the mother's blood. Low protein levels are typically indicative of a fetus with Down syndrome.

A test to detect positive often undergoes a complex invasion process including amniotic biopsy (to sample amniotic fluid) or to sample chorionic villus (placental biopsy) at 15 - 16 weeks of pregnancy age to check if the baby is born with Down syndrome. However, both of these tests lead to a high risk of miscarriage (ratio of 1/100). Therefore, scientists have long expected less invasive diagnostic methods for Down disease and other potential genetic problems.

New research to detect fetal Down syndrome through maternal blood (Photo: Daily mail).

Precursor to the new method

The goal of laboratory research is to test the accuracy of a new gene technique for Down syndrome, using blood samples from 80 confirmed pregnant women with Down syndrome through Other methods.

The study found a small amount of DNA from the fetus circulating in the mother's bloodstream during pregnancy . This process is called free fetal DNA . It was this finding that allowed researchers to test non-invasive methods to detect Down's disease and other genetic diseases using the mother's blood test.

The theory behind this study is based on the fact that some areas of the mother and fetus have different levels of metylano, a chemical transition that a methylano group binds to DNA. The researchers said non-invasive methods have been developed to detect ' different methylano-impregnated regions ' (DMR) between the mother's and fetal DNA. However, this method has many limitations.

Accurate and direct method

This method directly detects 3 chromosomes corresponding to number 21 by taking a small amount of blood from the mother during the 11th and 13th week of pregnancy . The researchers then measured the differences in DNA methylation patterns important to the level of gene control between the mother and fetus . Therefore, babies with Down syndrome will contribute more DNA with metylano from this chromosome in the mother's bloodstream . As a result, the DNA rate of metylano is higher than that of uninfected DNA in unborn babies.

From a prospective study of 80 women with blood samples taken between 11.1 and 14.4 weeks of pregnancy, the researchers took the test results by previous invasive methods and compared blood samples. of 40 pregnant women of these (of which 20 are diagnosed with a fetus with Down).

The researchers focused on observing the 12 known DNA regions with metylano levels in fetal DNA higher than the mother's DNA. They used a new technique called ' methylano DNA diffusion immunity ' to attach and separate methylano DNA from methylano-free DNA. They then used a standard technique to compare the proportion of DNA contaminated with methylano and not infected in blood samples.

In a small trial, scientists can correctly diagnose 14 cases of extra copies of chromosomes and 26 normal fetuses. This is the first experiment in the world to show 100% sensitivity and 100% specific determination of all mothers who are normal or pregnant with Down syndrome. According to the researchers, this method has a higher diagnostic sensitivity and is more specific than the method based on genetic information from blood samples and is more accurate than current ultrasound methods using translucency in the nape. (a special type of fetal scan) and biochemical measuring rod. They said this method could be carried out in basic diagnostic laboratories, easy to implement technically and at a lower cost than other genetic engineering technologies. Therefore, it can be used routinely for all pregnant mothers, avoiding the risk of miscarriage.