Chronic Granulomatous Disease Diagnosis
The correct answer is C: Catalase-producing bacteria are destroyed by the peroxide produced by neutrophils in healthy individuals, but NOT in CGD patients—this is the fundamental pathophysiology of the disease.
Why Each Answer is Right or Wrong
Option C is CORRECT
In healthy individuals, neutrophils produce hydrogen peroxide (H₂O₂) through the NADPH oxidase complex, which kills catalase-producing bacteria. In CGD, the defective NADPH oxidase cannot generate this peroxide, so catalase-producing organisms (like Staphylococcus aureus, Aspergillus, Burkholderia cepacia, Serratia, and Nocardia) survive and cause recurrent infections 1, 2. Catalase-negative organisms can be killed by their own peroxide production, which is why they rarely cause problems in CGD patients.
Option A is INCORRECT
CGD is primarily X-linked (approximately 60-70% of cases due to CYBB/gp91phox mutations), not autosomal recessive 3, 4. Autosomal recessive forms do exist (CYBA/p22phox, NCF1/p47phox, NCF2/p67phox, CYBC1/Eros deficiency) but are less common 3.
Option B is INCORRECT
This is backwards. CGD patients CANNOT handle catalase-producing organisms—these are precisely the pathogens that cause problems 1, 2. Catalase-negative organisms are typically handled normally because their own peroxide can be used for killing.
Option D is INCORRECT
Granulomatous lesions are indeed frequently observed—they are a hallmark of the disease (hence the name). Granulomas commonly occur in the gastrointestinal and genitourinary systems and can appear even before diagnosis 1. Both infections and inflammatory granulomas are characteristic features 3, 4.
Option E is INCORRECT
Staphylococcus aureus* is the most common bacterial pathogen, NOT *Streptococcus 1, 2. The typical pathogens in North America are S. aureus, Aspergillus species, Burkholderia cepacia complex, Serratia marcescens, and Nocardia species 1, 2.
Key Diagnostic Considerations
The dihydrorhodamine (DHR) flow cytometric assay is the gold standard screening test for CGD, measuring NADPH oxidase function quickly and cost-effectively 1, 5. This test can also identify X-linked carriers and help determine the inheritance pattern 5.
Common Pitfalls to Avoid:
- Don't confuse catalase-positive with catalase-negative organisms—CGD patients are susceptible to catalase-producing pathogens
- Remember that female X-linked carriers with unfavorable lyonization can present with partial or full CGD manifestations 4
- Residual NADPH oxidase activity significantly correlates with disease severity and survival 3, 6