Artemis: guarding small children and, now, the genome.

Through careful analysis of young patients exhibiting radiosensitivity and inherited SCID of B and T lymphocytes, Despina Moshous and colleagues discovered a new DNA repair gene two years ago and named it after the Greek goddess Artemis, a guardian of young children and small animals (1). The same group has recently analyzed several patients with hypomorphic Artemis mutations, and their results, published in this issue of the JCI (2), along with a recent report by the group of Fred Alt (3), have proven Artemis to be a guardian of the genome as well. To appreciate the significance of this finding, it is necessary first to review what is known about how our large repertoire of antigen receptors is generated.