A 3-year-old boy presents with recurrent infections with catalase-positive organisms, absolute lymphocyte count (ALC) is normal, immunoglobulins are normal. DHR flow cytometry shows absent oxidative burst. Genetic testing reveals a mutation in gp91phox (CYBB gene on X chromosome). His sister is asymptomatic with normal DHR test. The carrier mother's DHR test would be expected to show:
- A Normal DHR; the mother is unaffected and fully normal
- B Two distinct populations of neutrophils — one with normal oxidative burst and one with absent burst (bimodal pattern) ✓
- C Complete absence of oxidative burst, same as the affected son
- D Partial reduction of oxidative burst in all neutrophils uniformly
Explanation
X-linked CGD carrier mothers have one normal (gp91phox+) and one mutant (gp91phox-) X chromosome. Due to lyonisation (random X-inactivation), approximately 50% of their neutrophils will be derived from the cell line with the normal X (normal oxidative burst) and 50% from the cell line with the mutant X (absent burst). DHR flow cytometry in a carrier female demonstrates a characteristic bimodal/mosaic pattern — two populations of neutrophils — which is diagnostic of CGD carrier status. This bimodal pattern distinguishes the carrier from a normal female (all cells normal) and an affected male (all cells absent).
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.