They are required in DNA replication and repair processes in organisms such as bacteria and yeast, and RNase H1 knockout results in embryonic lethality in mice, defects in RNase H2 lead to autoimmune disorders, Aicardi–Goutières syndrome (AGS), systemic lupus erythematosus, and skin and intestinal cancers in humans (Arudchandran et al., 2000; Cerritelli et al., 2003; Crow et al., 2006; Tadokoro and Kanaya, 2009). The gene discussed is RNASEH1; the disease is Aicardi-Goutieres syndrome.