Aicardi-Goutières syndrome is an inherited subacute encephalopathy caused by mutations in TREX1, RNASEH2B, RNASEH2C, RNASEH2A, SAMHD1, ADAR1, IFIH1. All these AGS-related genes are involved in the nucleic acid metabolism or sensing, promoting, in physiological conditions, both the removal or identification of the presence of foreign nucleic acids. The gene discussed is SAMHD1; the disease is Aicardi-Goutières syndrome.