Usually, some degree of off-target activity is unavoidable, which is why every drug on the market carries warnings of side effects—but when it comes to gene editing, side effects could be especially dangerous. After all, the side effects of a medication typically cease once a patient stops taking the drug. With gene editing, however, any off-target DNA sequence, once edited, is irreversibly changed. Not only will unintended edits to the DNA be permanent, they will also be copied into every cell that descends from the first one.
