CYBB and chronic granulomatous disease: Additionally, mutations in the Cytochrome b-245 heavy chain (CYBB) gene encoding nicotinamide adenine dinucleotide phosphate (NADPH) oxidase catalytic gp91phox subunit causing X-linked chronic granulomatous disease (XCGD; a life-threatening primary immunodeficiency disorder16) can be functionally reconstituted in CYBB-null PLB (XCGD) cells17 engineered to express patient-specific CYBB mutations.