Chronic granulomatous disease (CGD) is characterized by severe, protracted and often fatal infections, which results from a failure of the NADPH oxidase enzyme system in the patient's phagocytes to produce reactive oxygen species (ROS). The NADPH oxidase enzyme is a system composed of a number of interacting cytosol and membrane components. The absence of any of the components causes failure of the system. Mutations in the genes coding various parts of the oxidase system cause CGD.