The results indicate that anti-Cit39-40 ACPA were detectable in the serum of 92% (83/90) of ACPA positive INA RA, 15% (6/40) of ACPA negative INA RA, 77% (20/26) of ACPA positive INA FDR, 7% (4/53) of ACPA negative INA FDR. This evidence concerns the gene PRTN3 and rheumatoid arthritis.