CYBB and chronic granulomatous disease: Chronic granulomatous disease (CGD) is caused by defects in nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) complex subunits (gp91phox (a.k.a. Nox2), p47phox, p67phox, p22phox, p40phox) leading to reduced phagocyte-derived reactive oxygen species production.