Novel mutations in CYBB Gene Cause X-linked chronic Granulomatous Disease in Pakistani patients

Chronic Granulomatous Disease (CGD) is a primary immunodeficiency that causes susceptibility to recurrent fungal and bacterial infections. The CYBB gene encodes gp91^phox component of the Phagocytic Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and specifically, X-linked CGD is caused by mutations in the CYBB gene, located on the X chromosome. The aim of the study was to characterize functional and genetic mutations in X-linked CGD.

Functional analysis was conducted on the whole blood of seventeen male individuals who were suspected to have X-linked chronic granulomatous disease (CGD). Flow cytometry was employed to assess the capacity of NADPH oxidase, measuring both H₂O₂ production and gp91^phox protein expression in neutrophils. Additionally, DNA Sanger sequencing was performed for genetic analysis. The pathogenicity of novel mutations was assessed by pathogenicity prediction tools.

Among the seventeen patients evaluated, five patients (P1, P2, P3, P4, and P5) displayed impaired H₂O₂ production by their neutrophils upon stimulation with Phorbol myristate acetate (PMA), accompanied by abnormal gp91^phox expression. DNA sequencing of the CYBB gene identified specific mutations in each patient. In P1 and P2 (previously reported cases), a hemizygous missense mutation, c.925G > A/p.E309K was identified. In P3 and P4 (novel cases), hemizygous nonsense mutations, c.216T > A/p.C72X were found. Lastly, in P5 (also a novel case), a hemizygous missense mutation, c.732T > G/p.C244W was detected. These mutations reside in exons 9,3 and 7 of the CYBB gene, respectively.

The current study contributes to the understanding of the clinical and genetic spectrum associated with X-linked chronic granulomatous disease (CGD). It highlights the significance of early diagnosis in CGD and emphasizes the importance of lifelong prophylaxis to prevent severe infections.