From superoxide, other ROS, such as hydrogen peroxide, can be generated. The exact mechanism of pathogen killing within the phagosome is not known. From the killing defect seen in CGD phagocytes, it is clear that ROS play an important role, but whether this is a direct role through formation of hypochlorous acid from hydrogen

peroxide and chloride, catalysed by myeloperoxidase, or an indirect role through facilitating the release of proteolytic enzymes from the granules in the phagocytes [2], or a combination of these mechanisms, remains to be established. Most CGD pathogens share the property ATM inhibitor of producing catalase; as such, they degrade the hydrogen peroxide that they themselves generate. It has therefore Palbociclib been suggested that catalase-negative organisms, by supplying the CGD phagocytes with microbial hydrogen peroxide, might complement the hydrogen peroxide deficit in CGD phagocytes, thus inducing killing of the microbes themselves. Catalase production was thus thought

to be an important microbial pathogenicity factor in CGD. However, this hypothesis must be viewed in the context that the majority of all pathogens contain catalase (with the important exception of streptococci). This view has been challenged further by the retained virulence of Aspergillus and staphylococci rendered genetically deficient for catalase production [3, 4]. In addition, individuals with the quite common deficiency of myeloperoxidase do not suffer from CGD-like symptoms. The genes encoding the five NADPH oxidase components are CYBB (located on the X chromosome)

for gp91phox, and the autosomal genes CYBA for p22phox, NCF1 for p47phox, NCF2 for p67phox and NCF4 for p40phox (Table 1). About 70% of the CGD patients have a mutation in CYBB (most of them hemizygous males, 4-Aminobutyrate aminotransferase but a few heterozygous females with skewed expression of their mutation are also known). The remainder of the patients have a mutation in NCF1 (about 20%), in CYBA (about 5%) or in NCF2 (about 5%). Only one patient is known with a mutation in NCF4. A mutation in any of these five genes can cause CGD. If the mutation leaves some residual NADPH oxidase activity intact, the clinical expression of the disease is less serious [5] and the chance of survival of the patient is larger [6] than in the case of total oxidase deficiency. This depends upon the gene mutated, the type of mutation and the position of the mutation within the gene. In general, mutations in NCF1 lead to a milder form of CGD (later presentation, milder clinical expression, better chance of survival) than mutations in any of the other genes. For genetic counselling and prenatal diagnosis, mutation analysis of the CGD genes is mandatory. Treatment should be started immediately after CGD has been definitely diagnosed, or even before.