What is the pathophysiology of chronic granulomatous disease (CGD)?

Updated: Jul 29, 2019
  • Author: Roman J Nowicki, MD, PhD; Chief Editor: Dirk M Elston, MD  more...
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Answer

Chronic granulomatous disease (CGD) is a genetically heterogeneous immunodeficiency disorder resulting from the inability of phagocytes to kill microbes they have ingested. This impairment in killing is caused by any of several defects in the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme complex, which generates the microbicidal respiratory burst. In CGD, phagocytes ingest bacteria normally, but they cannot kill them. [3]

Patients with CGD are susceptible to severe and recurrent infections due to catalase-positive organisms and organisms resistant to nonoxidative killing. Catalase-negative bacteria, such as streptococci and pneumococci that have the capacity to generate hydrogen peroxide, are killed as they usually are. The intracellular survival of ingested bacteria leads to the development of granulomata in the lymph nodes, skin, lungs, liver, gastrointestinal tract, and/or bones.

CGD is usually inherited in an X-linked recessive fashion. Most patients (approximately 80%) are males, who have hemizygous mutations on the X-linked gene coding for gp91phox. The gene responsible for this form of the disease has been mapped to the p21.1 region of the X chromosome. [4] However, among chronic granulomatous disease subtypes, the autosomal recessive (AR) forms may be associated with milder disease. The extent to which environmental and secondary genetic factors influence phenotypic expression of disease is unknown. A wide variety of molecular defects have been described in the genes for the gp91phox component, the p22phox component, [5] and the p67phox component. These defects include frame shifts; deletions; and nonsense, missense, splice-region, and regulatory-region mutations. [6, 7, 8]

In contrast, a GT deletion at the beginning of exon 2 accounts for the defective genetic function in almost all patients with p47phox deficiency. [9] Another protein, p40phox, has been implicated in the regulation of the NADPH oxidase, but no individual with a mutation in the protein has been found to date. A new variant of CGD has been described; this form is caused by an inhibitory mutation in Rac2, which regulates activity of the neutrophil respiratory burst and actin assembly. [10]


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