Residual NADPH Oxidase Activity and Isolated Lung Involvement in X-Linked Chronic Granulomatous Disease

Chronic granulomatous disease (CGD) is characterized by inherited immune defects resulting from mutations in the NADPH oxidase complex genes. The X-linked type of CGD is caused by defects in the CYBB gene that encodes gp91-phox, a fundamental component of the NADPH oxidase complex. This mutation originates the most common and severe form of CGD, which typically has absence of NADPH oxidase function and aggressive multisystemic infections. We present the case of a 9-year-old child with a rare CYBB mutation that preserves some NADPH oxidase activity, resulting in an atypical mild form of X-linked CGD with isolated lung involvement. Although the clinical picture and partially preserved oxidase function suggested an autosomal recessive form of CGD, genetic testing demonstrated a mutation in the exon 3 of CYBB gene (c.252 G>A, p.Ala84Ala), an uncommon X-linked CGD variant that affects splicing. Atypical presentation and diagnostic difficulties are discussed. This case highlights that the diagnosis of mild forms of X-linked CGD caused by rare CYBB mutations and partially preserved NADPH function should be considered early in the evaluation of atypical and recurrent lung infections.