MOLECULAR ANALYSIS IN 3 CASES OF X91(-) VARIANT CHRONIC GRANULOMATOUS-DISEASE

Defects in gp91-phox, the large subunit of cytochrome b(558) (b(-245)) give rise to X-linked chronic granulomatous disease (CGD), a rare inh erited condition characterized by an extreme susceptibility to bacteri al and fungal infection. In the majority of cases, the phagocytes are unable to generate any superoxide owing to complete absence of the fla vocytochrome. However, a small minority of these patients do have some phagocytic oxidase activity. We describe here an analysis of the mole cular basis of the disease in three such variant patients with lesions in the gene coding for gp91-phox on the X chromosome. Three different genetic lesions were found, resulting in the substitution of tyrosine for cysteine 244, a deletion of one of three lysines 313 through 315, and the deletion of the six C-terminal amino acids, respectively. The functional consequences of these defects on oxidase activity was a re duction to 12%, 3.6%, and 2.1% of the normal levels, respectively. Cor responding levels of gp91-phox were 20%, 8%, and 16% of normal classif ying these patients as X91(-). Microbicidal assays showed that killing of Staphylococcus aureus was grossly impaired in cells in which there was 12% normal activity. This implies that if gene therapy is to be a pplied, it must restore oxidase activity to a much higher level than t hat present in the cells of this patient. The sites of two of the muta tions were analyzed on a model of the C-terminal half of the gp91-phox , based on the crystal structure of the homologous protein ferrodoxin NADP reductase. Possible structural consequences of the mutations were examined. (C) 1995 by The American Society of Hematology.