Chronic granulomatous disease (CGD) is a primary immunodeficiency condition that is characterized by recurrent bacterial and fungal infections caused by an impaired phagocyte immune function. In patients with CGD, the production of reactive oxygen species, which is critical to phagocyte function, is defective, owing to a deficiency of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. The NADPH oxidase complex comprises subunits gp91-phox and p22-phox bound to the cell membrane, and cytoplasmic proteins p40-phox, p47-phox, p67-phox, and Ras-related C3 botulinum toxin substrate 2. The most common mutation in patients with CGD, accounting for almost 70% of all cases, is in the CYBB gene, located at chromosome Xp21.1, encoding gp91phox and transmitted in an X-linked pattern. However, numerous unique mutations in the other subunits have been described with varying frequencies.