PADI4 and arthritic joint disease: Interestingly, some RA patients develop autoantibodies against enzyme PAD4 (anti-PAD4 antibodies), which are used as biomarkers in RA patients [15]. The anti-PAD4 antibodies can be detected several years before the onset of arthritis in RA patients. Some researchers believe that anti-PAD4 antibodies are also disease severity biomarkers and have functional significance in adult patients with RA.