"This is the first example in which CRISPR-Cas9 is injected directly into the bloodstream — in other words systemic administration — where we use it as a way to reach a tissue that's far away from the site of injection and very specifically use it to edit disease-causing genes," says John Leonard, the CEO of Intellia Therapeutics, which is sponsoring the study.

Doctors infused billions of microscopic structures known as nanoparticles carrying genetic instructions for the CRISPR gene-editor into four patients in London and two in New Zealand. The nanoparticles were absorbed by their livers, where they unleashed armies of CRISPR gene-editors. The CRISPR editor honed in on the target gene in the liver and sliced it, disabling production of the destructive protein.

Within weeks, the levels of protein causing the disease plummeted. Researchers reported at the Peripheral Nerve Society Annual Meeting and in a paper published in The New England Journal of Medicine.