A Flawed Study Shows How Little We Understand Crispr's Effects

BIOTECH HAS BEEN betting big on Crispr, the gene-editing technique that promises to snip away some of humanity’s worst diseases. But last May, a small case study suggested the much-hyped technology might actually be quite dangerous—and pop went the Crispr bubble, briefly tanking shares of Crispr companies like Editas Medicine, Intellia Therapeutics, and Crispr Therapeutics.

It was an overreaction, as so many market spikes and dips turn out to be; the company CEOs were quick to push back, and scientists and journalists soon pointed out flaws in the paper that misconstrued cause and effect. After nearly a year of continued criticisms, and failures to reproduce the results, the authors conceded that the skeptics might be right. Last week, the journal that published the paper, Nature Methods, finally retracted it.

But that doesn’t mean that Crispr has been given the all-clear. The now-retracted paper claimed that Crispr caused nearly 2,000 unexpected mutations—ten times previously observed off-target rates—in two mice that it cured of blindness. But just as that evidence should never have been enough to squash Crispr’s clinical potential, neither...