PAD4 is one of the most highly correlated proteins in RA and has also been associated with cancer and metastasis.6,8,13,23,26,27 While its normal function is as a chromatin remodeler via histone citrullination, it also serves a key role in the unspooling of DNA during the process of macrophage cell death.9,26 During this process, PAD4 is released to the extracellular space where its hydrolytic activity can citrullinate extracellular proteins and cells in ways that are poorly understood.9,12,26,61. Here, PADI4 is linked to rheumatoid arthritis.