The neutrophil cytosolic factor 1 (NCF1) gene encodes one of five sub-units of the NADPH oxidase (NOX2) complex, which could produce ROS in the immune cells, including antigen presenting cells (APCs), phagocytes, etc. Olsson et al. (2012) found that RA patients are less likely to have an elevated copy number of NCF1 compared to controls, which may suggest that a higher copy number of NCF1 could be a protective factor for RA. Here, NCF1 is linked to rheumatoid arthritis.