They’re going to CRISPR people. What could possibly go wrong?

Now that a federal biosafety and bioethics committee has approved what would be the first use of the trailblazing genome-editing technology CRISPR-Cas9 in people, the obvious question arises: Could anything go wrong?

The purpose of such a Phase 1 clinical trial is to assess safety, so problems wouldn’t come as a total shock. The fact that the trial in cancer patients (which still needs OKs from the Food and Drug Administration, among others) would be funded by the new cancer institute founded this year by tech mogul Sean Parker adds a wild card. Four potential snafus:

1. CRISPR edits DNA it isn’t supposed to

Soon after scientists reported in 2012 that CRISPR can edit DNA, experts raised concerns about “off-target effects,” meaning genes that scientists didn’t intend to change inadvertently got deleted or altered. That can happen because one molecule in the CRISPR system acts as a molecular bloodhound, sniffing around the genome until it finds a match to its own sequence of A’s, T’s, C’s, and G’s; unfortunately, in the 6 billion such letters of the human genome, there can...