What are chronic granulomatous diseases (5 mark)
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chronic granulomatous disease NIAID NADPH oxidase overview
Chronic granulomatous disease (CGD) is a rare inherited primary immunodeficiency in which phagocytes, especially neutrophils and macrophages, cannot effectively kill certain ingested bacteria and fungi.
Cause and pathogenesis
- Caused by mutations affecting the phagocyte NADPH oxidase complex, most often X-linked.
- This causes failure of the respiratory/oxidative burst and deficient formation of superoxide and other reactive oxygen species.
- Microbes are ingested normally but not killed efficiently. Persistent infection leads to formation of granulomas.
Clinical features
- Begins usually in childhood with recurrent, severe bacterial and fungal infections.
- Common sites: lungs, lymph nodes, skin, liver, bones, and deep organs.
- May cause granulomatous inflammation leading to obstruction of hollow organs, for example intestinal or urinary obstruction.
Typical organisms
Especially susceptible to catalase-positive organisms, including:
- Staphylococcus aureus
- Serratia marcescens
- Burkholderia cepacia
- Nocardia
- Aspergillus species
Diagnosis
- Dihydrorhodamine (DHR) flow-cytometry test: reduced/absent oxidative burst. This is the preferred test.
- Nitroblue tetrazolium (NBT) test: fails to turn blue.
- Genetic testing confirms the responsible mutation.
Treatment
- Long-term antibacterial and antifungal prophylaxis, commonly trimethoprim-sulfamethoxazole and an azole antifungal.
- Interferon-gamma may reduce serious infections in selected patients.
- Prompt, intensive treatment of infections.
- Hematopoietic stem-cell transplantation can be curative.
CGD results from defective NADPH oxidase, so phagocytes cannot generate the oxidative burst needed to kill particular bacteria and fungi, as summarized by NIAID.
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