A would-be mom worried Down syndrome faces an unpleasant choice: undergo an invasive test that can kill the fetus, or forego a definitive answer until after birth. But a new method that involves tracing the differences between DNA and the mother of his baby could provide physicians with a safe and inexpensive way to diagnose the disease, a practice enough to become part of routine prenatal care.
Down syndrome is the most common genetic disease worldwide, affecting about one in 700 live births. Babies with the disease carry an extra copy of chromosome 21, which causes cognitive disorders, heart defects and other problems. Although certain markers in the blood of a mother can tip off doctors that the fetus is at risk for Down syndrome, only invasive and costly procedures such as amniocentesis, which requires poking a needle into the uterus to obtain a sample fluid may give an 99% accurate answer. But these invasive tests are risky: they can cause miscarriage in 1% to 2% of cases.
In an attempt to find a safer alternative, researchers have turned to the blood of the mother. In a recent study, scientists ferreted the fetal DNA fragments leaking into the bloodstream of the mother, and then sequenced genomes to check both additional copies of chromosome 21. These attempts were successful, but they were long and necessary DNA specialized and expensive equipment that would -sequencing the process out of reach for most people.
Philippos Patsalis wanted something more accessible. A geneticist at the Cyprus Institute of Neurology and Genetics in Nicosia Patsalis provided prenatal diagnostic tests for 20 years and has long lamented that women who want accurate testing face a higher risk and expense .
The first step was to find a simpler way of isolating fetal DNA from the blood stream of the mother. Instead of sequencing entire genomes, like the previous researchers did, Patsalis and colleagues focused on a process called DNA methylation. Here, called methyl groups attach chemicals to DNA regions and, as a volume knob on a stereo, turn up the activity of a gene or down. Fetus have methylation patterns that are different from their mothers, which allowed the group Patsalis easily distinguish the DNA of both in the blood of the mother.
Once the researchers had isolated fetal DNA, they began to look down syndrome signs. They have multiple copies of the DNA, then sought additional versions of chromosome 21. Again, methylation patterns simplified the process. Chromosome 21 has its own pattern of DNA methylation, which helped the team to find Patsalis additional copies easily.
The approach worked. Among 80 women who were pregnant 11-14 weeks the method was 100% accurate, using only standard equipment available in Basic Diagnosis Laboratory, Patsalis said. The findings, published online today in Nature Medicine "could blow the prenatal screening method in progress," says Joris Vermeesch geneticist from the University of Leuven in Belgium, which has not participated in the study. "This is the holy grail of prenatal diagnosis."
Patsalis's team has plans for large-scale clinical trials in the coming months. the simplicity, low cost and the potential of their method to identify other genetic conditions that makes them confident, Patsalis said the method "could be introduced in a clinical setting within 2 years."
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