Detection of CYBA Gene Expression by Reverse Transcription PCR as a Diagnostic Tool for Autosomal Recessive Chronic Granulomatous Disease in a Sample of Egyptian Children

Abstract

Abstract Chronic granulomatous disease (CGD) is an inherited primary immunodeficiency disease caused by functional impairment of the nicotinamide dinucleotide phosphate (NADPH) oxidase complex in neutrophilic granulocytes and monocytes, characterized by recurrent and severe infections, dysregulated inflammation, and autoimmunity. Approximately two-thirds of patients with CGD have defects in Cytochrome Bβ (CYBB), the X-linked gene encoding glycoprotein 91 phagocytic oxidase (gp91phox). Rarer autosomal recessive (AR) forms of CGD are caused by autosomal recessive mutations in CYBA genes encoding protein 22 phagocytic oxidase (p22phox). However, the incidence of autosomal recessive CGD can be higher than X-linked CGD in countries with high rates of consanguineous marriage. In the present study we aimed to diagnose the commonest AR-type of CGD by detection of CYBA gene expression using real time RT-PCR as a cheaper diagnostic method for CGD subtypes categorization among immunodeficient children. This case-control study was conducted on 15 children provisionally diagnosed as CGD patients with DHR stimulation index using phorbol myristate acetate (PMA) < 30% (Group I). The study also included 12 mothers and 8 fathers of the studied patients to detect the genetic mutations in carriers, if any (Group IIa and IIb respectively), and 14 apparently healthy children as a control group (Group III). We found that cases with a fold change of CYBA gene expression less than 0.6 were considered under-expressed. At this cut-off value, from our molecularly studied subjects 1 case and 2 mothers showed under-expression of CYBA gene. In conclusion, we could establish the diagnosis of AR-form of CGD, derives from defects in the CYBA gene, which encodes p22phox of the NADPH oxidase using real time RT-PCR, without the need to use complex and expensive methodologies such as northern blot, slot blot, or genomic DNA sequencing.