In an effort to repair a gene that causes blindness, researchers using a CRISPR DNA-cutting machine accidentally got rid of entire chromosomes, or large chunks of them, according to a study published Thursday in the journal Cell.
For the study, researchers at an undisclosed lab collected sperm from a man with hereditary blindness to create 40 embryos.
They then used a CRISPR-Cas9 tool — which functions like a microscopic scalpel — to cut out the gene mutation they wanted to correct in 37 of the embryos. The remaining three were serving as controls.
But about half of the embryos lost an entire chromosome, or large swaths of it, on the gene where the mutation causing blindness was located, according to the study.
Removed or damaged chromosomes can result in genetic abnormalities that can be passed on to future generations.
“This is a very adverse outcome,” study author Dieter Egli, of Columbia University, told the Wall Street Journal.
The findings also show the “the human embryo seems unique in its poor ability to fix a DNA break,” Egli said, who added that it goes “beyond the debate” over the use of CRISPR in pregnancies.
Scientists have for years debated whether CRISPR is safe and effective enough to use on human embryos that will eventually grow into babies.
Critics point to studies showing the technology can cause cancer, while others argue that it is not yet precise enough.
Other skeptics take issue with the ethics of allowing scientists to “play God.”
Last month, a group sponsored by the US National Academy of Medicine published a report saying the technology isn’t ready to be used on embryos because scientists don’t yet know how to use it without introducing potentially dangerous DNA changes.