The U.S. Food and Drug Administration recently approved the first gene editing treatments for sickle cell disease. Co-developed by Vertex Pharmaceuticals and CRISPR Therapeutics, the exa-cel treatment uses new technology to modify a gene involved in red blood cell shape and function. It is too early to say whether the treatment will be permanent and without side effects, as only about 100 people have undergone the procedure, and they have been followed for less than two years.

According to the National Institutes of Health, sickle cell disease is a group of genetic disorders that affect hemoglobin, the protein that carries oxygen to the body. In sickle-cell patients, red blood cells are crescent-shaped and do not bend, instead of being disc-shaped and flexible. This anomaly can block blood flow to the body, leading to strokes, eye problems, infections, fatigue and severe pain. Until now, a bone marrow transplant was the only cure. 

CRISPR technology—short for clustered regularly interspaced short palindromic repeats—allows scientists to strategically modify the DNA of organisms. The exa-cel treatment involves removing a patient’s bone marrow stem cells, editing them using the CRISPR technology, destroying the untreated bone marrow and re-infusing the modified cells to replicate and repopulate the body.