The hereditary autoinflammatory diseases arise from mutations of genes regulating the innate immune system. These rare disorders are well characterized, both clinically and in terms of their molecular pathogenesis. The recurrent attacks of febrile polyserositis of Familial Mediterranean Fever (FMF) are due to defective pyrin, a protein that down-regulates inflammation. The Hyperimmunoglobulinemia D Syndrome (HIDS), which mimics FMF, results from a genetically conferred deficiency of mevalonate kinase. TRAPS (TNF Receptor Associated Periodic Syndrome), formerly known as Familial Hibernian Fever, is caused by a defective membrane receptor for TNF. Three other hereditary disorders which overlap in their clinical expression - Familial Cold Autoinflammatory Syndrome, the Muckle Wells syndrome, and Neonatal Onset Multisystem Inflamatory Disease (NOMID) - are a consequence of gain-of-function mutations of the gene encoding cryopyrin, the scaffolding protein of the inflammasome. The PAPA syndrome (Pyogenic Arthritis, Pyoderma gangrenosum, Acne) results from mutations of a gene that increases the binding of its product (PSPSTPIP1) to pyrin, thereby blunting the inhibitory effect of pyrin on inflammasome activation.