On December 8, 2023, the U.S. Food and Drug Administration (FDA) approved Casgevy , the first gene therapy utilizing clustered, regularly interspaced short palindromic repeats (CRISPR) for the treatment of sickle cell disease in patients 12 years and older. Mimicking a protective mutation that causes fetal hemoglobin (HbF) to persist into adulthood, Casgevy uses the CRISPR-Cas9 enzyme to edit a patient’s own blood stem cells to intentionally disable a DNA “brake” on HbF production. The modified stem cells are transplanted back to the patient and result in the production of high levels of HbF, preventing the sickling of red blood cells and eliminating or greatly reducing future painful vaso-occlusive (VOC) crises. In an ongoing single-arm trial— initial results were published in 2020 —29 out of 31 treated patients had no severe VOC episodes for at least 12 consecutive months during the 24-month follow-up period. The approval of Casgevy, which has a list price of $2.2 million for the s