CYBB and chronic granulomatous disease: Although there are a number of genes involved in the ROS-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex, the mutation of any of which can result in CGD, the majority of cases (>60%) are due to loss of function of the cytochrome b-245 heavy chain (CYBB) protein (or GP91PHOX) [11].