Obstetricians routinely test for Down’s syndrome by injecting a large needle into an expectant mother’s womb to pull out a small sample of the surrounding fluid or tissue that is then screened for the presence of extra chromosomes. But such invasive procedures, which include amniocentesis and chorionic villus sampling, carry a small but appreciable risk of miscarriage, so researchers have been on the hunt for safer alternatives.
One approach under development involves a simple blood test followed by next-generation DNA sequencing. For example, in January Dennis Lo and his colleagues at the Chinese University of Hong Kong reported that sequencing maternal blood plasma can detect Down’s syndrome with greater than 98% accuracy. But tests like these are expensive, requiring machines not yet available in most hospitals.
Now, in a study published online yesterday in Nature Medicine, a team led by Philippos Patsalis of the Cyprus Institute of Neurology and Genetics unveiled a lower cost alternative that relies on DNA methylation profiling instead of full genome sequencing. In the study, the authors showed that their assay was 100% accurate in diagnosing 14 cases of Down’s syndrome with no false positives associated with 26 healthy fetuses.
The approach “has opened the way for noninvasive prenatal diagnosis of Down’s syndrome to be potentially employed in the routine practice of all diagnostic laboratories and be applicable to all pregnancies.” Patsalis told The Telegraph newspaper.
Patsalis’ test relies on quantitative PCR to compare the levels of methylation in the maternal and fetal DNA — a measure of gene regulation and expression that serves as a good proxy for chromosome number.
Looking ahead, clinical geneticists may be more likely to adopt the methylation-based assay for routine screening because the test is a lot cheaper than those that rely on newer sequencing technologies. In fact, Patsalis expects the test to hit the clinic within the next two years, ScienceNOW reports.
To find out more about the non-invasive blood tests being developed for Down’s syndrome and their impact going forward, check out this month’s Community Corner and the accompanying podcast, which features an interview with Stanford bioengineer Stephen Quake.