CGD is characterised by four major clinical features, reviewed in [1,2,11,24,25,26,27,28,29]: (1) predisposition to infection by a classically described subset of catalase-positive bacteria and fungi; (2) development of tissue granulomas in respiratory, gastrointestinal and genitourinary tracts, which may lead to local complications; (3) predisposition to inflammatory bowel disease (IBD), which may be very early in onset and severe; and (4) other autoinflammatory or autoimmune complications. Here, CAT is linked to chronic granulomatous disease.