FMO5 and chronic granulomatous disease: However, even though cell-free NADPH activation seems to be impaired when the cytosol of neutrophil is depleted of small GTPases and recombinant Rap1A is able to restore NADPH oxidase activation, normal levels of Rap1A have been identified in neutrophil membranes from patients with CGD, suggesting that the absence the cytochrome b558 does not affect the expression of this protein and its presence in the membrane [61].