ADAR and Aicardi-Goutieres syndrome: In AGS, ADAR mutations are most often a compound heterozygote, with a frequent pattern being where one allele has a mutation impacting the p150 isoform (e.g., p.P193A) and a second mutation impacting the deaminase domain or leading to loss of the ADAR1 protein (Rice et al. 2012, 2017).