DNA Shed By Embryos Could Offer Non-Invasive Testing
A small pilot study presented at the European Society for Human Reproduction and Embryology 2018, suggest that DNA shed from early embryos could one day provide an alternative way of genetically testing them without having to do a biopsy.
Currently, preimplantation genetic diagnosis (PGS) and preimplantation genetic diagnosis (PGD) involve taking a cell from the in vitro embryo at the blastocyst stage — this cell is biopsied and the DNA examined. As well as being invasive, only one cell is examined so the test cannot identify mosaicism in the embryo.
Although the researchers acknowledged that their study had a limited number of samples, they aimed to explore whether DNA shed by the embryo into its culture medium could be used instead — similar to the way NIPT works, where fetal DNA can be isolated from the mother’s bloodstream.
“The question is whether this external DNA is detectable from the spent culture media,” said Dr. Carmen Rubio of Igenomix.
“Is embryo cell-free DNA in the media representative if the chromosomal constitution of the blastocyst?”, she asked.
Dr. Rubio and her team carried out a pilot study that looked at 115 blastocysts from 39 PGT-A cycles, a form of PGS which analyses the chromosomal content of a single cell taken from the blastocyst aiming to identify chromosomally normal embryos for implantation.
“The results are really, really very similar,” she said of the comparison between the test methods.
Previous smaller studies that compared cell-free DNA from the embryo and DNA obtained from cell biopsy found that the two methods returned the same results in 80% of samples.
The main challenges in the culture medium approach are maternal DNA contamination and the possibility of embryo mosaicism.
“If we can improve this technique, in the future it may be a replacement for biopsy,” Dr. Rubio added.
However, experts have previously argued that this approach may lead to viable embryos being discarded unnecessarily.