Base editing in human embryos advances, but mosaicism limits its use
Researchers reported in Nature that they used base editing — a next-generation CRISPR tool that swaps individual DNA letters without cutting the double helix — to edit early human embryos while probing how a gene central to early development functions.
The work also exposed a persistent obstacle. The edits did not take hold consistently in every cell, leaving embryos as a patchwork of altered and unaltered cells, a problem known as mosaicism. A separate study published weeks earlier reported similar results, suggesting the limitation is not a one-off.
The findings sharpen a long-running debate. More precise editing tools raise the theoretical prospect of correcting disease-causing mutations, but the same capabilities feed concerns about trait selection and enhancement. The mosaicism issue, together with safety and ethical questions, means the technique remains far from any use that would produce a pregnancy.