Conversely, a reduction in Nox2 oxidase activity due to mutations in the genes that encode Nox2 (Cybb), or any one of the three NADPH oxidase regulatory subunits, p22phox, p47phox or p67phox, underpins the condition known as chronic granulomatous disease (CGD), characterised by an inability of phagocytes to mount a respiratory burst to kill ingested pathogens, and leading to severe life-threatening infections by opportunistic bacteria and fungi [15], [16]. This evidence concerns the gene FMO5 and chronic granulomatous disease.