TREX1 and systemic lupus erythematosus: This is apparently what happens constitutively in patients with loss-of-function mutations in TREX1. It also appears to occur in at least a subset of SLE patients: the second messenger 2’3’-cyclic-guanosine-adenosine-monophosphate (cGAMP), which is synthesized exclusively by cGAS upon DNA binding, was detected by mass spectrometry in 7 of 30 SLE patients (198).