JAK1 and rheumatoid arthritis: The Janus kinase (JAK) family of non-receptor protein tyrosine kinases (JAK1, JAK2, JAK3, and tyrosine kinase 2 [TYK2]) plays a crucial role in multiple cytokine receptor signaling pathways [4] and is a promising target for RA treatment in patients with insufficient response to DMARDs and biologic agents.