JAK1 and rheumatoid arthritis: JAK1 also plays a crucial role in the pathology of arthritis, while JAKis are used in treatment of RA: tofacitinib (TOF, JAK1/3 inhibitor); peficitinib (pan JAK inhibitor); baricitinib (BAR, JAK1/2 inhibitor); upadacitinib (JAK1/2 inhibitor); and filgotinib‐target JAK1.2