SAMHD1 and Aicardi-Goutieres syndrome: AGS is an early onset Type 1 interferonopathy that presents with an uncontrolled Type 1 interferon (IFN) response, similar to systemic lupus and congenital viral infections (10–12) Although over 50% of AGS patients have been identified with mutations in RNASEH2A/RNASEH2B/RNASEH2C, others have also been found with mutations in TREX1, SAMHD1, ADAR1 and IFIH1 (9,13–15).