The Promise and Peril of Crispr

Tracy Antonelli and her three daughters suffer from thalassemia, a blood disorder that saps their strength, leaves them anemic, and requires them to visit Boston Children’s Hospital every three weeks for transfusions. “We’re lucky we have a treatment regimen that’s available to us, but it’s cumbersome,” Antonelli says.

A technology in development at several drug companies offers some hope for a more effective and convenient treatment for the Antonellis, and patients with other serious genetic conditions, such as sickle cell anemia. The technique is called Crispr, which stands for clustered regularly interspaced short palindromic repeats. Crispr, a method for editing the human genome—the complete set of an individual’s genetic material present in any of her cells—allows scientists to cut out faulty sections of DNA that can lead to serious illnesses and replace them with healthy ones. In the two-part process, first an RNA “guide” molecule locates the part of the DNA that needs to be removed or fixed. Then a Cas9 protein attaches to the DNA and cuts out the mutation. In some cases, scientists can then insert...