CYBC1 (cytochrome b-245 chaperone 1) functions as an essential chaperone protein for stable expression of the CYBA (p22phox) and CYBB (gp91phox) subunits of the cytochrome b-245 heterodimer, a critical component of the phagocyte NADPH oxidase complex 1. This enzyme produces reactive oxygen species (ROS), including superoxide and hydrogen peroxide, which are essential for intracellular killing of pathogens by phagocytic leukocytes 2. CYBC1 thus controls the phagocyte respiratory burst and is essential for innate immunity 3. Mutations in CYBC1 cause chr17 granulomatous disease (CGD), autosomal recessive type 5, characterized by loss of respiratory burst and gp91phox expression in phagocytes 4. CYBC1-CGD patients present with severe recurrent bacterial and fungal infections, with inflammatory bowel disease being the most common inflammatory manifestation, occurring at a significantly higher rate than other CGD forms 5. Beyond immune function, CYBC1 drives glioblastoma progression via NOXA1-mediated ROS production and NF-κB pathway activation, with elevated CYBC1 expression correlating with poor patient survival 6. Clinically, CYBC1 deficiency diagnosis utilizes dihydrorhodamine assay testing phagocyte respiratory burst capacity 4. Current treatments include antimicrobial and antifungal prophylaxis, hematopoietic stem cell transplantation (84-90% survival), and emerging gene therapy approaches 4.