New York: 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.
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