FDA expands Casgevy gene therapy to children as young as 2 for sickle cell and beta-thalassemia

The U.S. Food and Drug Administration on Tuesday expanded the use of Vertex Pharmaceuticals’ Casgevy to children as young as 2 with sickle cell disease or transfusion-dependent beta-thalassemia, lowering the eligible age from 12 and making it the first gene therapy approved for patients 2 and older with sickle cell disease.

The July 1 supplemental approval gives younger children access to a one-time treatment made from their own gene-edited blood stem cells. The new indication covers patients age 2 and older with sickle cell disease marked by recurrent vaso-occlusive crises — painful episodes caused by blocked blood flow — or with transfusion-dependent beta-thalassemia, a blood disorder that requires regular red blood cell transfusions.

The expansion matters because Casgevy was previously cleared only for patients 12 and older. FDA officials said making the therapy available earlier could open a window to reduce disease burden and the risk of lasting organ damage in children, though the pediatric label expansion was not based on large amounts of direct data in toddlers and preschool-age children.

Instead, the agency relied on results from studies in children ages 5 to under 12 and extrapolated from those findings to support approval down to age 2. In sickle cell disease, the cited trial enrolled 11 children, with eight evaluable for efficacy; all eight met the primary endpoint of having no protocol-defined severe vaso-occlusive crises for at least 12 straight months within the first 24 months after infusion. In transfusion-dependent beta-thalassemia, the cited trial enrolled 15 children, with nine evaluable for efficacy; eight of nine achieved transfusion independence for 12 consecutive months, with a median duration of 20.1 months.

Casgevy is an autologous therapy, meaning it is made from a patient’s own hematopoietic, or blood-forming, stem cells. It uses CRISPR/Cas9 gene editing to modify the BCL11A enhancer, a DNA control region, to raise production of fetal hemoglobin. Higher fetal hemoglobin can reduce the red blood cell sickling that drives sickle cell disease and can reduce or eliminate the need for transfusions in beta-thalassemia.

But the treatment is far from a simple infusion. Patients first undergo stem-cell collection, then receive full myeloablative conditioning — high-intensity chemotherapy designed to wipe out existing bone marrow cells — before getting the edited cells back in a one-time infusion. The therapy is available only at specialized treatment centers authorized by the manufacturer, a constraint that can limit practical access.

FDA said common adverse reactions seen in the pediatric data included mucositis, a painful inflammation and ulceration of the mouth and digestive tract lining, and febrile neutropenia, a dangerous combination of fever and very low infection-fighting white blood cells. In sickle cell disease patients, decreased appetite was also among the common side effects. The prescribing information carries warnings for neutrophil engraftment failure, delayed platelet engraftment, hypersensitivity reactions and the risk of off-target genome editing.

The FDA announcement did not detail serious events beyond the label warnings. But in a December 2025 clinical update, Vertex disclosed that one child in the pediatric program died from pneumonia in the setting of multi-organ failure due to severe veno-occlusive disease related to busulfan conditioning, the chemotherapy used before infusion.

“With today’s decision, pediatric patients as young as 2 years of age can now access a critical additional treatment option to treat these debilitating, life-threatening diseases,” said Karim Mikhail, acting director of the FDA’s Center for Biologics Evaluation and Research.

Casgevy was one of the first CRISPR-based medicines approved in the United States when FDA first cleared it in December 2023. FDA said the latest age-expansion application was completed 53 days after filing under the agency’s Commissioner’s National Priority Voucher pilot program.