In a significant breakthrough, scientists at a US-based gene analytics firm claimed that they can decode almost all the DNA of days-old embryos created via in vitro fertilisation (IVF), the Science reported.
According to MyOme, full sequence of both parents’ DNA and resulting “reconstruction” of an embryo’s genome with the help of the data, could make it possible to forecast risk for common diseases including heart conditions, autoimmune diseases, cancer, that can develop later in life. The advance is currently available only for adults.
In a paper, published in the journal Nature Medicine, the MyOme team described creating such scores by first sequencing the genomes of 10 pairs of parents who had already undergone IVF and had babies.
The researchers then used data collected during the IVF process: The couples’ embryos, 110 in all, had undergone limited genetic testing at that time, a sort of spot sequencing of cells, called microarray measurements.
Such analysis can test for an abnormal number of chromosomes, certain genetic diseases, and rearrangements of large chunks of DNA. By combining these patchy embryo data with the more complete parental genome sequences, and applying statistical and population genomics techniques, the researchers could account for the gene shuffling that occurs during reproduction and calculate which chromosomes each parent had passed down to each embryo. In this way, they could predict much of that embryo’s DNA, the report said.
The researchers collected cheek swab samples from the babies and sequenced their full genome, just as they’d done with the parents. They then compared that “true sequence” with the reconstructed genome for the embryo from which the child originated.
The comparison revealed, essentially, a match: For a 3-day-old embryo, at least 96 per cent of the reconstructed genome aligned with the inherited gene variants in the corresponding baby; for a 5-day-old embryo, it was at least 98 per cent, the report said.
Once the embryo genomes were reconstructed, the researchers turned to published data from large genomic studies of adults with or without common chronic diseases and the polygenic risk score models that were derived from that information. Then, they applied those models to the embryos, crunching polygenic risk scores for 12 diseases, including breast cancer, coronary artery disease, and Type 2 diabetes.
The team also experimented with combining the reconstructed embryo sequence of single genes, such as BRCA1 and BRCA2, that are known to dramatically raise risk of certain diseases, with an embryo’s polygenic risk scores for that condition-in this case, breast cancer.
The rise of such complex genetic testing in human embryos is alarming, experts argued in a report in Nature. It is because people undergoing IVF are then offered the chance to select an embryo with a perceived low relative risk of developing such diseases. Further, such tests could trigger the unnecessary destruction of viable embryos or induce women to undergo extra cycles of ovarian stimulation to collect more oocytes.