The U.K.’s medicines regulator, the Medicines and Healthcare Regulatory Agency, has approved the world’s first gene therapy treatment for sickle cell disease. The treatment, called Casgevy, uses the gene editing tool CRISPR to target the problematic gene in a patient’s bone marrow stem cells and allow the body to produce properly functioning hemoglobin. Casgevy was approved for patients aged 12 and over with sickle cell disease and thalassemia. The decision was based on studies showing positive results, with patients reporting no severe pain problems for at least one year after treatment. The treatment is currently being reviewed by the U.S. Food and Drug Administration.