TYK2 and type 1 diabetes mellitus: In the early stage of T1D, TYK2—a candidate gene in T1D—plays a critical role in beta cells following viral infection (e.g., via polyinosinic-polycytidylic acid, a viral RNA mimic) or cytokine stimulation (e.g., IFN-α), where it mediates IFN-I signaling (7, 8).