Mutations in the XIAP gene were found to result in a primary immunodeficiency condition in humans, named X-linked lymphoproliferative syndrome 2 (XLP2, OMIM entry number: 300635) [23], while XIAP polymorphisms are responsible for idiopathic periodic fever [24], suggesting that XIAP may play a key role in immune homeostasis. The gene discussed is XIAP; the disease is X-linked lymphoproliferative disease.