FMO5 and chronic granulomatous disease: Being a monogenic disorder, the rationale for gene therapy of CGD patients lacking a HLA-matched donor is well-established on the following grounds—a) all the genes affecting NADPH oxidase subunits have been cloned, and b) data from healthy X-CGD carriers have revealed that significant functional correction of a minor fraction of neutrophils (approximately 10%) can benefit the patient considerably.