Nesrine Radwan
Lecturer in Paediatrics, Ain Shams University, Egypt.

Background: CGD is an immunodeficiency disease caused by mutations in genes encoding subunits of the leukocyte NADPH oxidase complex causing defective “respiratory burst”, and thus failure of clearance of micro-organisms. Its prevalence is 1∶250,000. The majority of CGD patients suffer from severe recurrent bacterial and fungal infections, dysregulated Th-17-lymphocyte-controlled inflammation causing granuloma formationand autoimmune phenomena. The most common offending organisms are Staphylococcus aureus, and Aspergillus. The leukocyte NADPH oxidase, consists of subunits, four of which are important for CGD; gp91phox ,p22phox (located in membranes) and p47phox, p67phox ( located in the cytosol). gp91phox gene mutations  are  responsible for 70% of CGD cases which are inherited as  X-linked recessive. Mutations in the other subunits  are   autosomal recessive in inheritance (figure 1)1. Treatment includes long-term prophylactic  antibiotics and antifungals and curative stem-cell transplantation.

Case Report: Herein, we present a 24 months’ old boy, first in birth order of a non-consanguinous parents who suffered of recurrent abscesses in thighs and buttocks since the age of 12 months. At the age of 18 months, he had severe gastroenteritis requiring hospital admission. Moderate hepatomegaly with raised transaminases was noted during admission. Abdominal US showed multiple hepatic abscesses requiring ultrasound guided drainage and prolonged IV AB with negative cultures. He has normal growth and no dysmorphic features. Laboratory data showed slight leukocytosis (15.4x109/L) with neutrophilia (42%),   hypergammaglobulinemia   and normal lymphocyte subsets.  Dihydrorhodamine assay (DHR) showed defective neutrophil response to E-Coli (25.7%)(figure 2). Flowcytometry showed normal expression of CGD proteins (gp91,p67,p47). DHR for the mother confirmed carrier status with defective response to E-coli with two peaks (16.9%) (figure 2). Genetic testing for CGD is awaited.

Discussion: It has been shown that survival of patients with CGD is strongly associated with residual reactive oxygen intermediate (ROI) production,independent of the specific gene defect. 2 Measurement of NADPH oxidase activity through the  DHRflow cytometry assay contributed to the assessment of ROI. Activation of neutrophils with phorbol myristate acetate (PMA) or E-coli results in oxidation of DHR to a fluorescent compound, rhodamine 123, which can be measured by flow cytometry. Flow cytometry can distinguish between the different genetic forms of CGD3.  Most cases with XL CGD have absent neutrophil DHR activity, while in 17% of cases neutrophil can maintain some DHR activity 4. Residual activity above 10% is associated with a mild-moderate disease severity. Normal protein expression by western blot or flowcytometry does not exclude the disease as it might be a non-functioning protein. Definitive diagnosis is done by genetic sequencing.

Figure 1:Cartoon illustrating the NADPH oxidase complex in phagocytes and the related voltage-gated proton channel. In a resting phagocyte (neutrophil, macrophage, or eosinophil), gp91 phox and p22 phox are present in the membrane as a heterodimer, and the other four components are located in the cytosol. Upon stimulation by various agents, all the components assemble to form a functional complex.

Figure(2a): Patient’s DHR shows impaired response to E-coli in comparison to unstimulated tube

Figure(2b): Maternal DHR shows impaired response to E-coli in comparison to unstimulated tube with two peaks

References:
1-    [20] DeCoursey, T.E. (2003) Physiol. Rev. 83, 475^579.
1.    De Coursey TE (2003), Physiol rev .83, 475-579
2.    Kuhns DB, Alvord WG, Heller T. N Engl J Med 2010;363:2600-2610
3.    Vowells SJ, Fleisher TA, Sekhsaria S, et al (1996) J Pediatr, 128:104-107.
4.    Jirapongsananuruk O, Malech HL, Kuhns DB, Niemela JE, Brown MR, Anderson-Cohen M, Fleisher TA (2003).J Allergy Clin Immunol ,111(2):374-9.