The gene-editing technique known as CRISPR (clustered regularly interspaced short palindromic repeats) is only 5 years old, yet it has galvanized biomedical research and raised important ethical questions. What is it, how does it work, and how could it change medical practice?

Biomedical scientists have been “editing” (or, at least, altering) genes for many years. Recombinant DNA technology allowed particular genes to be inserted into a plasmid (a circle of DNA) or into a virus: bacterial and yeast cells now could produce therapeutically useful human proteins, and viral vectors could perform gene therapy in humans. Gene targeting and RNA interference allowed the knockout of particular genes and the insertion of a healthy gene at the site of a defective gene. Zinc finger proteins and transcription activator-like effector nucleases (TALENs) precisely altered specific genes. Then came CRISPR. Compared with these previous technologies, CRISPR is easier, faster, less expensive, and more powerful.