AGBL2 and rheumatoid arthritis: Among the 402 RA patients included in the KAc-His2B and anti-MAA screening, 70 individuals (17.4%) were seronegative for both CCP2 IgG and RF IgM, the tests used in the clinic, but of these only 17 (i.e. 4.2% of the total RA study population) were negative in all available autoantibody tests.