Characterization of six novel mutations in the CYBB gene leading to different sub-types of X-linked chronic granulomatous disease

Abstract

Chronic granulomatous disease is an inherited disorder in which phagocytes lack a functional NADPH oxidase and so cannot generate superoxide anions (O2-). The most common form is caused by mutations in CYBB encoding gp91 phox , the heavy chain of flavocytochrome b558 (XCGD). We investigated 11 male patients and their families suspected of suffering from X-linked CGD. These XCGD patients were classified as having different variants (X910, X91- or X91+ b558 expression and NADPH oxidase activity. Nine patients had X910 CGD, one had X91- CGD and one had X91+ CGD. Six mutations in CYBB were novel. Of the four new X910 CGD cases, three were point mutations: G65A in exon 2, G387T in exon 5 and G970T in exon 9, leading to premature stop codons at positions Try18, Try125 and Glu320, respectively, in gp91 phox. One case of X910 CGD originated from a new 1005G deletion detected in exon 9. Surprisingly, four nonsense mutations in exon 5 led to the generation of two mRNAs, one with a normal size containing the mutation and the other in which exon 5 had been spliced. A novel X91- CGD case with low gp91 phox expression was diagnosed. It was caused by an 11-bp deletion in the linking region between exon 12 and intron 12, activating a new cryptic site. Finally, a new X91+ CGD case was detected, characterized by a missense mutation Leu505Arg in the potential NADPH-binding site of gp91 phox. No clear correlation between the severity of the clinical symptoms and the sub-type of XCGD could be established. © Springer-Verlag 2004.