Importantly, mice with a Treg-specific deletion of either Dicer (12–14) or Drosha (15), the 2 ribonuclease III (RNase III) enzymes necessary for the production and processing of mature miRNA species, also develop a spontaneous, lethal autoimmune disease virtually indistinguishable from that seen in Scurfy mice (7), demonstrating that miRNAs are critical for establishment of Treg-mediated peripheral tolerance. Here, DROSHA is linked to autoimmune disease.