Scientists for the first time have successfully edited genes in human embryos to repair a common and serious disease-causing mutation, producing apparently healthy embryos, according to a study published on Wednesday.
The researchers averted two important safety problems: They produced embryos in which all cells – not just some – were mutation-free, and they avoided creating unwanted extra mutations.
In these embryos, the sperm cell’s mutant gene ignored that template and instead copied the healthy DNA sequence from the egg cell.
Some embryos had cells that did not get repaired – a phenomenon called mosaicism that could result in the mutation being passed on – as well as unplanned mutations that could cause other health problems.
For these parents, gene editing could help by repairing mutant embryos so that more disease-free embryos would be available for implantation. Another 13 embryos also emerged without the mutation, but not in every cell.
The remaining 16 embryos had unwanted additions or deletions of DNA. Dr. Mitalipov said he believed fine-tuning the process would make at least 90 percent of embryos mutation-free.