SAMHD1 and Aicardi-Goutieres syndrome: AGS also results from defects in RNAse H2, which cleaves RNA from DNA to decrease DNA damage, and SAM and HD Domain Containing Deoxynucleoside Triphosphate Triphosphohydrolase 1 (SAMHD1), a dNTPase that acts at stalled replication forks and regulates reverse transcription to cDNA (128–130).