ADAR and Aicardi-Goutieres syndrome: The three other genes that can induce AGS are homozygous loss-of-function mutations in the gene for “adenosine deaminase acting on RNA 1” (ADAR1), IFIH1 which encodes MDA5, and the gain-of-function variant of TMEM173 which encodes constitutively active STING (the direct effector protein for cGAS, Figure 1C) and results in the constitutive activation of this pathway in the absence of aberrant DNA (80).