Researchers at Reprogenetics have published a study demonstrating the high accuracy of a new technique, called array CGH (aCGH), for analysis and screening of all chromosomes in human embryos. The authors report that errors or potential misdiagnoses occur very rarely with this technique. In the case of individual blastomeres from day-3 embryos, the error rate is only 1.8%, despite complications arising from mosaic embryos; these are embryos with a mix of normal and abnormal cells. They are known to occur frequently in vitro and can cause non-technical diagnostic errors during PGD. Further research at Reprogenetics has shown the accuracy of aCGH for blastocyst (day-5) biopsies to be 100% (unpublished data). This is clearly very encouraging.
The error rate published by Gutierrez and co-workers was obtained through the full analysis of all blastomeres in embryos that were previously analyzed and excluded from transfer based on chromosomal and other abnormalities; the results of the reanalysis were then compared with the original results obtained based on analysis of one (day-3) or a few cells (day-5). The 1.8% error rate indicates that only 2 of every 100 embryos had discordant results, that is, they were classified as abnormal but were not entirely abnormal; none of those classified as normal was found to be abnormal.
Many laboratories do not publish error rates which is problematic because they have no reference point for the results they produce. In our view, reanalysis of embryos using either the same technique or another technique as a quality control measure is critical for genetic testing laboratories. Implementation of such Quality Control/Quality Assurance measures sets Reprogenetics apart from many of its competitors.
“We now think that although mosaicism is very common in human embryos, a majority of mosaic embryos are what we call chaotic mosaics, resulting from a random distribution of chromosomes from cell division to cell division. Analysis of all chromosomes in every cell in these embryos shows that the likelihood of one cell having a normal chromosome count is slim to none. With previous techniques, not all chromosomes were analyzed; some cells appeared to be normal for the chromosomes analyzed, suggesting that mosaic embryos could produce a misdiagnosis.” Comments Santiago Munné, President of Reprogenetics and senior author on the article.
For more information: PubMed
1 Gutierrez-Mateo et al. Fertility and Sterility, 2011, 95:953-958