A team from Columbia University, led by geneticist Dieter Egli, has managed to edit genes in human embryos with unprecedented precision using a technique known as base editing. The advance, published as a preprint and currently under peer review, represents a qualitative leap over conventional CRISPR, which in previous studies by the same group had shown “catastrophic” results when trying to modify embryonic DNA.
Unlike traditional CRISPR, which cuts both strands of DNA as if they were molecular scissors —and which in human embryos caused the complete destruction of the chromosome in roughly half of cases—, base editing makes a small nick in a single strand and uses a chemical enzyme to convert one DNA letter into another. The result is a much cleaner modification, without the extensive chromosomal damage that made the previous approach unviable.
The researchers managed to successfully modify two different genes in early human embryos: the PCSK9 gene, whose mutations raise the risk of heart disease by increasing LDL cholesterol in the blood, and the HBG gene, which controls the production of fetal hemoglobin. In some experiments, they managed to edit both genes simultaneously in the same embryo, opening the door to correcting multiple inherited mutations in a single procedure.
However, the study is not without limitations and controversy. The scientists detected that some embryos showed a mosaic pattern, that is, cells where the editing did not occur and which retained the original version of the gene. In addition, the work has rekindled intense bioethical debates about the limits of gene editing in human embryos, especially after the scandal of Chinese scientist He Jiankui, who in 2018 used CRISPR to create the first genetically modified babies and was sentenced to three years in prison.
Dieter Egli has been cautious in assessing the results: “We are not saying this is going to be used in clinics tomorrow,” he said. “As a scientist, you can provide the data for the debate, but then basically you stop there and let others continue”. The embryos used in the experiment were donated by parents undergoing fertility treatments and none was implanted for development.
The study has received funding from Nucleus Genomics, a company that analyzes in vitro fertilization embryos, which has added more fuel to the ethical debate. Critical voices such as geneticist Fyodor Urnov (UC Berkeley) warn that this type of research could provide “an instruction manual for baby designers to push beyond the ethical limit”. For now, the scientific community awaits the peer review to confirm the validity and reproducibility of the finding.
