For that reason, the authors of the report lay out exactly how many and what kind of off-target effects might be acceptable. They put that threshold at no more than the average rate of new mutations an embryo spontaneously acquires. DNA replication isn’t perfect, and most people are born with a few dozen mutations that don’t exist in either of their biological parents’ genomes. Gene editing shouldn’t introduce any more genetic variations than occur naturally, the authors concluded, and the types of changes should be carefully studied in the lab to make sure they don’t lead to adverse outcomes.
The trouble is, though, that right now there aren’t any good methods for assessing off-target effects in embryos. Doing so requires collecting large amounts of DNA, which can only be done by sacrificing a number of cells from the embryo for genetic sequencing. In addition to being unreliable, these methods harm