TREX1 and Aicardi-Goutieres syndrome: AGS can result from loss-of-function (or specific dominant-negative) mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR1, gain-of-function mutations in IFIH1 (Lehtinen et al., 2008; Rice et al., 2007a).