The loss-of-function mutations in a DNA-specific exonuclease gene TREX1, resulting in increased cytosolic DNA levels, are observed in the type I interferonopathies Aicardi-Goutieres syndrome (AGS) and chilblain lupus (Crow et al., 2006; Günther et al., 2013). The gene discussed is TREX1; the disease is Aicardi-Goutieres syndrome.