Doctors hope the one-time treatment, which involves permanently altering DNA in blood cells with a tool called CRISPR, may treat and possibly cure sickle cell disease and beta thalassemia.
Victoria Gray, the first patient in the sickle cell study, had long suffered severe pain bouts that often sent her to the hospital.
In sickle cell, defective hemoglobin leads to deformed, crescent-shaped blood cells that donโt carry oxygen well.
The treatment involves removing stem cells from the patient's blood, then using CRISPR in a lab to knock out the switching gene.
Williams, who was not involved in Frangoulโs study, said it โvalidates this approachโ of targeting the hemoglobin switching gene to tackle sickle cell.