Knockout of TREX1 (three-prime repair exonuclease 1), a nuclease that is mutated in Aicardi–Goutières syndrome and systemic lupus erythematous and that has been shown to degrade cytosolic L1 DNA4,27,29, increased both baseline and decitabine-induced interferon levels (Fig. 3g). Here, TREX1 is linked to Aicardi-Goutieres syndrome.