SAMHD1 and Aicardi-Goutières syndrome: Aicardi-Goutieres syndrome (AGS) is an early-onset encephalopathy that can be caused by a gene mutation in one of 7 discovered genes so far (TREX1, RNASEH2B, RNASEH2C, RNASEH2A, SAMHD1, ADAR1, and IFIH1) [55].