CGD is a genetically heterogeneous disease with an X-linked recessive (XR-CGD) form caused by mutations in the CYBB (OMIM #300481) gene encoding the gp91(phox) protein, and an autosomal recessive (AR-CGD) form caused by mutations in the CYBA (OMIM #608508), NCF1 (OMIM #608512), NCF2 (OMIM #608515) and NCF4 (OMIM #601488) genes encoding p22(phox), p47(phox), p67(phox) and p40(phox), respectively.