TREX1 and Encephalopathy: Aicardi–Goutières syndrome (AGS) is a genetically determined encephalopathy caused by mutations in any one of the nine genes [TREX1 (3' repair exonuclease 1), RNASEH2A (ribonuclease H2 subunit A), RNASEH2B, RNASEH2C, SAMHD1 (SAM-domain- and HD-domain-containing protein 1), ADAR1 (adenosine deaminase acting on RNA 1), IFIH (interferon induced with helicase C domain 1), LSM11, and RNU7-1] [1–3].