CYBB encodes the gp91-phox subunit (also known as NOX2), which serves as the catalytic component of the phagocyte NADPH oxidase complex responsible for generating superoxide anions essential for microbial killing 1. The enzyme transfers electrons from cytosolic NADPH to molecular oxygen, producing superoxide that serves as a precursor for hydrogen peroxide and other reactive oxygen species used by neutrophils and other phagocytes for antimicrobial defense 1. CYBB expression is regulated by NF-κB through a distant upstream binding site located 15 kb from the promoter region 2. Mutations in CYBB cause X-linked chrX granulomatous disease (CGD), the most severe form of this primary immunodeficiency, resulting in greatly increased susceptibility to severe bacterial and fungal infections due to defective phagocyte oxidative metabolism 34. Beyond antimicrobial function, NOX2 plays regulatory roles in various pathological processes, including obesity-mediated atrial fibrillation through oxidative stress mechanisms 5 and sepsis-related organ dysfunction via neutrophil extracellular trap formation 6. Gene editing approaches using CRISPR/Cas9 are being developed as potential curative treatments for CGD patients 7.