Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder. : 149   FMF is an autoinflammatory disease caused by mutations in Mediterranean fever gene, which encodes a 781–amino acid protein called pyrin. While all ethnic groups are susceptible to FMF, it usually occurs in people of Mediterranean origin—including Sephardic Jews, Mizrahi Jews, Ashkenazi Jews, Assyrians, Armenians, Azerbaijanis, Levantines, Kurds, Greeks, Turks and Italians.The disorder has been given various names, including familial paroxysmal polyserositis, periodic peritonitis, recurrent polyserositis, benign paroxysmal peritonitis, periodic disease or periodic fever, Reimann periodic disease or Reimann syndrome, Siegal-Cattan-Mamou disease, and Wolff periodic disease. Note that "periodic fever" can also refer to any of the periodic fever syndromes. Signs and symptoms
Attacks
There are seven types of attacks. Ninety percent of all patients have their first attack before they are 18 years old. All develop over 2–4 hours and last anywhere from 6 hours to 5 days. Most attacks involve fever. Abdominal attacks, featuring abdominal pain, affect the whole abdomen with all signs of peritonitis (inflammation of abdominal lining), and acute abdominal pain like appendicitis. They occur in 95% of all patients and may lead to unnecessary laparotomy. Incomplete attacks, with local tenderness and normal blood tests, have been reported. Joint attacks mainly occur in large joints, especially in the legs. Usually, only one joint is affected. 75% of all FMF patients experience joint attacks. Chest attacks include pleuritis (inflammation of the pleura) and pericarditis (inflammation of the pericardium).
Various mutations of this gene lead to FMF, although some mutations cause a more severe picture than others. Mutations occur mainly in exons 2, 3, 5 and 10.The function of pyrin has not been completely elucidated, but in short, it is a protein that binds to the adaptor ASC and the pro form of the enzyme caspase-1 to generate multiprotein complexes called inflammasomes in response to certain infections. In healthy individuals, pyrin-mediated inflammasome assembly (which leads to the caspase 1) dependent processing and secretion of the pro-inflammatory cytokines (such as interleukin-18 (IL-18) and IL-1β) is a response to enterotoxins from certain bacteria. The gain-of-function mutations in the MEFV gene render Pyrin hyperactive, and subsequently, the formation of the inflammasomes becomes more frequent.The pathophysiology of familial Mediterranean fever has recently undergone significant advances: at basal state, pyrin is kept inactive by a chaperone protein (belonging to the family of 14.3.3 proteins) linked to pyrin through phosphorylated serine residues. The dephosphoration of pyrin is an essential prerequisite for the activation of the pyrin inflammasome. Inactivation of RhoA GTPases (by bacterial toxins, for example) leads to the inactivation of PKN1 / PKN2 kinases and dephosphoration of pyrin. In healthy subjects, the dephosphorylation step alone does not cause activation of the pyrin inflammasome. In contrast, in FMF patients, the dephosphorylation of serines is sufficient to trigger the activation of the pyrin inflammasome. This suggests that there is a two-level regulation and that the second regulatory mechanism (independent of (de)phosphorylation) is deficient in FMF patients.