SAMHD1 and Aicardi-Goutieres syndrome: Nine genes are implicated in AGS etiology, each integral to pathways of nucleic acid metabolism and sensing including TREX1, RNASEH2A, RNASEH2B, RNASEH2C, ADAR, SAMHD1, IFIH1, LSM11, and RNU7-1309,312–317.