Reengineering Life

Scientists Edited Human Embryos in the Lab, and It Was a Disaster

The experiment raises major safety concerns for gene-edited babies

Emily Mullin
Published in
5 min readJun 16, 2020


Photo illustration, sources: Wellcome Trust, ZEPHYR/Science Photo Library/Getty Images

Reengineering Life is a column from OneZero about the astonishing ways genetic technology is changing humanity and the world around us.

A team of scientists has used the gene-editing technique CRISPR to create genetically altered human embryos in a London lab, and the results of the experiment do not bode well for the prospect of gene-edited babies.

Biologist Kathy Niakan and her team at the Francis Crick Institute wanted to better understand the role of a particular gene in the earliest stages of human development. So, using CRISPR, they deleted that gene in human embryos that had been donated for research. When they analyzed the edited embryos and compared them to ones that hadn’t been edited, they found something troubling: Around half of the edited embryos contained major unintended edits.

“There’s no sugarcoating this,” says Fyodor Urnov, a gene-editing expert and professor of molecular and cell biology at the University of California, Berkeley. “This is a restraining order for all genome editors to stay the living daylights away from embryo editing.”



Emily Mullin

Former staff writer at Medium, where I covered biotech, genetics, and Covid-19 for OneZero, Future Human, Elemental, and the Coronavirus Blog.