SAMHD1 and Aicardi-Goutieres syndrome: Seven genes have been reported to result in the classical AGS phenotype: three prime repair exonuclease 1 (TREX1; AGS1), ribonuclease H2 subunit B (RNASEH2B; AGS2), RNASEH2C (AGS3), RNASEH2A (AGS4), SAM and HD domain containing triphosphate triphosphohydrolase 1 (SAMHD1; AGS5), adenosine deaminase acting on RNA (ADAR1; AGS6) and interferon induced with helicase C domain 1 (IFIH1; AGS7) [3–6].