Novel mutations in the <i>CYBB</i> gene causing X-linked chronic granulomatous disease: a case report of 2 patients

Introduction: Chronic granulomatous disease (CGD) is an inherited primary immunodeficiency caused by mutations in the NADPH complex characterized by recurrent infections, inflammation and autoimmunity. While autosomal recessive forms exist, X-linked CGD makes up the majority of cases, which is caused by mutations in the CYBB gene. Patients are at high risk for infections with catalase positive bacteria and fungi. The prognosis has improved significantly with improvements in disease detection and management, including prophylactic antibiotic and antifungal therapy. Hematopoietic stem cell transplantation (HSCT) is a curative option for patients with a suitable donor. Aim: To report the clinical presentation, immune features and genetic mutations in 2 patients with novel mutations in the CYBB gene causing X-linked CGD who underwent HSCT. Results: Case 1: Patient 1 is a 14-year-old patient who initially presented with disseminated aspergillosis at the age of 3. He was noted to have an abnormal neutrophil oxidative burst index (NOBI) and genetic testing revealed a mutation in the CYBB gene (c.883_87dupGTGGT) consistent with CGD. He successfully underwent HSCT at age 4. At age 10 he developed a primary intracranial rhabdomyosarcoma in the posterior cranial fossa. Case 2: Patient 2 is a 4-year-old male who was worked up for CGD after developing a perianal abscess at 1 month of age followed by Moraxella bacteremia at 2 months of age. He had 2 abnormal NOBIs and genetic testing identified a novel mutation in the CYBB gene that was thought to explain his phenotype (c.941delA). He underwent an HSCT (10/10 HLA matched unrelated donor). Both patients have had normalization of their NOBI post-transplant and remain free of significant infections. Discussion: We report the clinical presentation, immune features and genetic mutations in 2 patients with novel mutations in the CYBB gene causing X-linked CGD. Identifying pathogenic mutations causing CGD is important for a better understanding of genotype–phenotype associations and disease course in this patient population. Statement of novelty: We describe 2 pediatric patients diagnosed with X-linked chronic granulomatous disease due to novel mutations in the CYBB gene.

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