Vertex Pharmaceuticals and CRISPR Therapeutics said the FDA has expanded the approved age range for Casgevy, the CRISPR/Cas9 gene-edited cell therapy known chemically as exagamglogene autotemcel, to include children as young as two years old with severe sickle cell disease (SCD) or transfusion-dependent beta thalassemia (TDT). The decision, announced this week, marks the first time a CRISPR-based medicine has been cleared for use in toddlers.

The approval rests on data from an expanded pediatric cohort within the ongoing CLIMB studies, the same trial framework that supported Casgevy’s original 2023 clearance in patients twelve and older. In the SCD portion of the pediatric extension, all eight evaluable patients remained free of vaso-occlusive crises for at least twelve consecutive months following a single infusion, a bar the original adolescent and adult cohorts also cleared at high rates. Vaso-occlusive crises, the painful blockages of blood flow that define sickle cell disease and frequently land patients in the emergency room, are the primary driver of morbidity in the condition and the endpoint regulators have consistently anchored to across the sickle cell gene therapy class.

Casgevy works by editing the BCL11A gene in a patient’s own hematopoietic stem cells, removing a genetic brake that normally suppresses production of fetal hemoglobin after infancy. Once reinfused, the edited cells produce fetal hemoglobin at levels high enough to compensate for the defective adult hemoglobin that causes red blood cells to sickle. The one-time procedure requires myeloablative conditioning chemotherapy beforehand, a regimen that has limited uptake in very young patients until now, given concerns about fertility and long-term development in a population still years from puberty.

Extending eligibility downward matters commercially and clinically. Sickle cell disease is typically diagnosed at birth through newborn screening, and clinicians have long argued that intervening before cumulative organ damage from repeated crises sets in offers the best chance at durable benefit. Vertex has priced Casgevy at $2.2 million per patient in the U.S., and payer negotiations for pediatric coverage will likely follow a similar outcomes-based reimbursement structure to the one Vertex established for the adolescent and adult population.

The competitive backdrop remains crowded. Bluebird bio’s Lyfgenia, a lentiviral gene therapy for SCD, and a growing list of earlier-stage editing approaches from companies including Beam Therapeutics continue to vie for the same patient pool, though none has yet secured pediatric clearance at this age threshold. For clinical operations teams running rare disease pediatric studies, the pediatric extension also underscores how regulators are increasingly willing to accept small, single-arm cohorts with durable biomarker follow-up as sufficient evidence, a pattern that mirrors the pragmatic trial designs favored by contract research organizations managing rare disease programs across multiple sites, including in the Asia-Pacific region where patient identification and screening infrastructure for hemoglobinopathies continues to mature.

Vertex said it expects the first pediatric infusions under the expanded label to begin within the next quarter, pending completion of authorized treatment center certification for the younger age group.