A new method for non-invasive prenatal testing is described in an Online Article published today (Friday February 2, 2007) by The Lancet.
Currently, available tests for prenatal diagnosis of chromosomal abnormalities—eg, trisomy 21, which causes Down's syndrome—are limited by several factors. Screening tests, such as ultrasound, are non-invasive, but diagnosis requires further invasive testing. Invasive diagnostic tests, such as amniocentesis and chorionic villus sampling, are associated with risks to the pregnancy. Development of non-invasive tests that yield diagnostic results would be an important advancement in prenatal care.
Ravinder Dhallan (Ravgen Inc, Columbia, MD, USA) and colleagues took blood samples from 60 pregnant women and extracted fetal DNA from these samples. The investigators examined the samples of fetal DNA for chromosomal abnormalities by analysing an array of single nucleotide polymorphisms (SNPs, pronounced "snips")—tiny variations in the DNA sequence of individuals. The researchers established the ratio of SNPs on different chromosomes, which enabled them to determine whether the fetus had chromosomal abnormalities. Of the 60 samples tested, the technique identified the number of chromosomes correctly in 58, including two cases of trisomy 21. Although one case of trisomy 21 was not identified, and one normal sample was incorrectly identified as being trisomy 21, the researchers stress that this is a preliminary study, and that further trials are needed to fine tune the technique.
The authors state that "[blood samples] are done routinely in clinical settings and present little risk to the mother and fetus", and conclude that, "with further refinement, a prenatal diagnostic test based on the methods [that we have developed] could be a useful complement to currently available prenatal tests."
Embargo: 6:30pm ET Thursday February 1, 2007 in North America.
See accompanying Comment Dr Ravinder Dhallan, Ravgen Inc, Columbia, MD, USA. T) Cell phone: +410 340 8125 Office phone: +410 715 2111 ext. 104 rdhallan@ravgen.com
Journal
The Lancet