By the time many couple’s get to the point of an IVF pregnancy, they have already had extensive medical testing and often unpleasant medical procedures, often at a considerable cost. For this reason, prenatal and preimplantation tests to ensure the maximum chance of a healthy pregnancy are popular in this group of prospective parents.
Polygenic risk scores for the purposes of embryo testing have been available for a couple of years in the U.S. and New Jersey-based biotech Genomic Prediction specializes in helping couples pick the right embryo for implantation purposes.
The technique to sample and sequence cells from an embryo at the preimplantation stage is not technically very difficult, and very accurate, according to Shai Carmi, an associate professor in statistical and population genetics at the Hebrew University of Jerusalem, who has recently published a paper analyzing the accuracy of polygenic risk scores like those used by Genomic Prediction for embryo selection.
“In a sense it’s kind of revolutionized the way preimplantation genetic diagnosis is performed, because instead of doing a separate test for mutation and a separate test for aneuploidy you can just do whole genome sequencing of embryos,” said Carmi. “You can do a very low coverage, very cheaply and get all the information that you need.”
Carmi’s recent paper, published in eLife, evaluated using polygenic risk scores to predict the risk for diseases such as schizophrenia and Crohn’s disease to assess the risk for later development of these conditions linked to each embryo.
“If they have just one embryo, it’s pointless to do this, but let’s say there is a young couple, and they have five embryos, they can compute the polygenic risk score for any disease they want in any of their embryos. And then they can compare the embryos and pick the embryo that is the best according to their criteria,” explained Carmi.
He and his colleagues found that picking the embryo with the lowest score for a given disease did appear to reduce future risk for that condition, although notably carrier risk from the parents did not seem to influence an embryo’s future disease risk to a great degree.
Although Carmi acknowledged that the predictive accuracy of such testing is unclear, as no IVF babies born using this technology have yet lived to an age they might experience these common diseases being tested for, he thinks it still has merit as a selection method.
“Right now, the practice is to select the embryo just based on the way it looks under the microscope and it’s kind of arbitrary. If you say, ‘okay, let’s look at the genetics and pick the embryo with better genetics,’ maybe it’s not something very radical that we’re doing here.”
He added that in the future, when the accuracy of these tests improves, “we may even get to a situation where clinicians in the U.S. will have to offer this or they will be at risk of lawsuits if they don’t offer it.”