IFIH1 and Aicardi-Goutieres syndrome: Besides ADAR1, eight disease‐causative mutations have been identified in AGS, including gain‐of‐function mutations in IFIH1 (encoding MDA5), all of which cause an elevated type I IFN signature (Livingston & Crow, 2016; Rodero & Crow, 2016; Uggenti et al, 2019, 2020).