The finding that a rare monogenic form of lupus can also be caused by mutations in TREX1 (Lee-Kirsch et al., 2007a; Rice et al., 2007a) or SAMHD1 (Ravenscroft et al., 2011), as well as the identification of SLE patients carrying mutations in TREX1 (Lee-Kirsch et al., 2007b) and a report of the coexistence of AGS and SLE in a patient with mutated SAMHD1 (Ramantani et al., 2011), further underpinned the tight pathogenetic relationship between AGS and SLE. The gene discussed is SAMHD1; the disease is systemic lupus erythematosus.