Indeed, MPO-ANCAs have been reported in systemic lupus erythematosus (SLE; 9.3%) [11], rheumatoid arthritis (RA; 4–18%) [12], Sjögren’s syndrome (SS; <3%) [13] and systemic sclerosis (SScl; <2.4%) [14]. This evidence concerns the gene MPO and rheumatoid arthritis.