Familial Mediterranean fever
Familial Mediterranean fever is a hereditary inflammatory disorder. 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, Arabs, 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 4 days. Most attacks involve fever.- Abdominal attacks, featuring abdominal pain, affect the whole abdomen with all signs of peritonitis, 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 and pericarditis. Pleuritis occurs in 40% of patients and makes it difficult to breathe or lie flat, but pericarditis is rare.
- Scrotal attacks due to inflammation of the tunica vaginalis are somewhat rare but may be mistaken for testicular torsion.
- Myalgia
- Erysipeloid
- Fever without any of the other symptoms listed above. Fever may be the only symptom during the childhood. It may vary from a mild fever to 38–40 °C. It nearly always accompanies to episodes.
Complications
There appears to be an increase in the risk for developing particular vasculitis-related diseases, spondylarthropathy, prolonged arthritis of certain joints and protracted myalgia.
Genetics
The MEFV gene is located on the short arm of chromosome 16. Many different mutations of the MEFV gene can cause the disorder. Having one mutation is unlikely to cause the condition. Having two mutations either a copy from both parents, or two different mutations, one from each parent is the threshold for a genetic diagnosis of FMF. However, most individuals who comply with the genetic diagnosis of FMF remain asymptomatic or undiagnosed. Whether this is due to modifier genes or environmental factors remains to be established.Pathophysiology
Virtually all cases are due to a mutation in the Mediterranean Fever gene on the sixteenth chromosome, which codes for a protein called pyrin or marenostrin. 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 dependent processing and secretion of the pro-inflammatory cytokines 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 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 leads to the inactivation of PKN1 / PKN2 kinases and dephosphoration of pyrine. 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 pyrine inflammasome. This suggests that there is a two-level regulation and that the second regulatory mechanism is deficient in FMF patients. This deficient mechanism is probably located at the level of the B30.2 domain where most of the pathogenic mutations associated with FMF are located. It is probably the interaction of this domain with the cytoskeleton that is failing, as suggested by the efficacy of colchicine.
It is not conclusively known what exactly sets off the attacks, and why overproduction of IL-1 would lead to particular symptoms in particular organs.
Diagnosis
The diagnosis is clinically made on the basis of the history of typical attacks, especially in patients from the ethnic groups in which FMF is more highly prevalent. An acute phase response is present during attacks, with high C-reactive protein levels, an elevated white blood cell count and other markers of inflammation. In patients with a long history of attacks, monitoring the kidney function is of importance in predicting chronic kidney failure.A genetic test is also available to detect mutations in the MEFV gene. Sequencing of exons 2, 3, 5, and 10 of this gene detects an estimated 97% of all known mutations.
A specific and highly sensitive test for FMF is the "metaraminol provocative test ", whereby a single 10 mg infusion of metaraminol is administered to the patient. A positive diagnosis is made if the patient presents with a typical, albeit milder, FMF attack within 48 hours. As MPT is more specific than sensitive, it does not identify all cases of FMF, although a positive MPT can be very useful.
Treatment
Attacks are self-limiting, and require analgesia and NSAIDs. Colchicine, a drug otherwise mainly used in gout, decreases attack frequency in FMF patients. The exact way in which colchicine suppresses attacks is unclear. While this agent is not without side effects, it may markedly improve quality of life in patients. The dosage is typically 1–2 mg a day. Development of amyloidosis is delayed with colchicine treatment. Interferon is being studied as a therapeutic modality. Some advise discontinuation of colchicine before and during pregnancy, but the data are inconsistent, and others feel it is safe to take colchicine during pregnancy.Approximately 5–10% of FMF cases are resistant to colchicine therapy alone. In these cases, adding anakinra to the daily colchicine regimen has been successful. Canakinumab, an anti-interleukin-1-beta monoclonal antibody, has likewise been shown to be effective in controlling and preventing flare-ups in patients with colchicine-resistant FMF and in two additional autoinflammatory recurrent fever syndromes: mevolonate kinase deficiency and tumor necrosis factor receptor-associated periodic syndrome.