Fionn Mulrooney, a cheerful 11-month-old, in Plymouth, Massachusetts, has no idea he has a life-threatening genetic disease. Nor does he seem fazed by the daily subcutaneous injections his parents have learned how to give him. And little does he know that cells from his bone marrow are helping scientists develop an innovative gene-editing approach that could someday correct his disease, known as severe congenital neutropenia, or SCN. Daniel Bauer, MD, PhD, is experimenting with editing the DNA of stem cells from patients’ own bone marrow to enable the cells to make neutrophils. The edited stem cells would then be returned to the patient’s body, going back to the bone marrow. Like many patients with SCN, Fionn has a mutation in a gene called ELANE. Hundreds of ELANE mutations are known, and all disrupt formation of neutrophils by altering the structure of a protein called elastase. The mutated elastase can’t fold into its proper configuration, causing the precursors of neutrophils to die rather than maturing into functional neutrophils.
