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