Susceptibility to systemic autoimmunity in patients with CGD is likely to be directly mediated by lack of NAPDH oxidase activity rather than indirect effects of having CGD per se, as heterozygous female carriers of the X-linked cytochrome b-245, β polypeptide (Cybb) null allele also have a higher likelihood of developing SLE, despite not having CGD (13, 14). This evidence concerns the gene CYBB and systemic lupus erythematosus.