For several years, scientists have experimented on human embryos with a powerful genome editing tool called CRISPR to see if they could correct genetic errors or reduce the risk of disease. In September, Kathy Niakan at the Francis Crick Institute in London and her colleagues reported they had used this tool on human embryos for a very different purpose — to better understand human development.
The use of CRISPR (pronounced “crisper”) to modify human embryos has prompted a healthy debate on the ethics of human genetic technologies. This tool is controversial, in part, because changes that are made to the embryo could be passed down to future generations. Niakan’s recent research is novel, and less ethically fraught than some other genome-editing research.
Research labs around the world are using CRISPR to selectively insert, delete or replace DNA with far greater precision and at a lower cost than other genome-editing techniques. Since 2015, five reports have detailed its use in human embryos to correct disease-causing mutations or create resistance to infectious disease.
Scientists have modified the genes responsible for β-thalassemia (an...