Advances in the understanding of familial Mediterranean fever and possibilities for targeted therapy

Familial Mediterranean fever (FMF) is a systemic autoinflammatory disorder characterized by seemingly unprovoked recurrent episodes of fever and serosal, synovial, or cutaneous inflammation. FMF is caused by recessively inherited mutations in MEFV, which encodes pyrin, and most of the mutations are present in the C-terminal end of the protein encoding B30.2 domain. The FMF carrier frequencies are extremely high in several eastern Mediterranean populations. Pyrin is expressed in granulocytes, monocytes, dendritic cells, and synovial fibroblasts. Pyrin regulates caspase-1 activation and consequently interleukin-1beta production through the interactions of its N-terminal PYRIN domain and C-terminal B30.2 domain with an adaptor protein, apoptosis-associated speck-like protein with a caspase-recruitment domain (ASC) and caspase-1 respectively. Pyrin is cleaved by caspase-1 and the cleaved N-terminal fragment translocates to nucleus and enhances ASC-independent nuclear factor (NF)-kappaB activation through interactions with p65 NF-kappaB and IkappaB-alpha. In addition to the regulatory role of pyrin for caspase-1, the cleavage of pyrin provides an important clue not only in understanding the molecular pathogenesis of FMF but also in developing new therapeutic targets for FMF.