[Familial Mediterranean Fever (FMF): from diagnosis to treatment]

Familial Mediterranean Fever (FMF), also known as paroxysmal polyserositis, is an autosomal recessive disease affecting mainly Mediterranean populations (Jews, Armenians, Arabs, Turks). It is characterised by recurrent crises of fever and serosal inflammation, leading to abdominal, thoracic or articular pain. Erysipela-like erythema affecting mainly feet and legs and effort-induced myalgia are less frequently encountered symptoms. The major complication of FMF is the development of renal amyloidosis. Standard laboratory tests of FMF patients are non-informative, except for the high sedimentation rate and white blood cell count, but during and immediately after crises, diminished albumin concentrations and elevated fibrinogen, C-reactive protein, beta2 and alpha2 M globulins, haptoglobin and lipoprotein concentrations are noted. Studies have measured immunoglobulin (Ig) levels in the sera of FMF patients and found elevated levels of IgA, IgM, IgG, and IgD in 23%, 13%, 17% and 13%, respectively. FMF crises are characterised by a massive influx of polymorphonuclear leukocytes into the inflamed regions. Moreover, the peritoneal fluid of FMF patients contains abnormally low levels of the inhibitor of complement fragment C5a and interleukin 8. Failure to suppress inflammatory response to C5a may explain the typical inflammatory FMF crises. The MEFV (for MEditerranean FeVer) gene responsible for the disease has been identified on 16p13.3. It is composed of 10 exons and spans approximately 14 Kb of genomic DNA. More than 35 mutations have so far been identified. The most frequent are M694V, M694I, M680I, V726A and E148Q. The M694V mutation is the most frequent mutation in the various ethnic groups considered, although its frequency varies from group to group. The V726A mutation is observed mainly among Ashkenazi and Iraqi Jews, Druzes and Armenians, and the M680I among Armenians and Turks. M694I and A744S seem specific to Arab populations, and R761H is frequently found in Lebanese FMF patients. The M694V mutation is often correlated with severe phenotypes, mainly in the homozygous state. It has been specifically correlated with arthritis, pleuritis and especially amyloidosis. Patients with other mutations in the 694 and 680 codons can also have severe phenotypes. The V726A mutation, although identified in FMF patients with a relatively mild phenotype, has also been detected in patients with renal amyloidosis. E148Q is often associated with a mild phenotype, and whether it is even a polymorphism has been questioned. The MEFV gene codes for a protein that was respectively called pyrin and marenostrin by the French and international consortia that simultaneously identified the gene. Its function is still not determined, but it was recently colocalised with microtubules and actin filaments in the cytoplasm. It contains a death domain called PYD (Pyrin Domain), usually associated with proteins involved in apoptosis. Some genes have been tested to assess their possible modifying effects on clinical features of FMF. The alpha/alpha genotype of the serum amyloid A or SAA1 gene is associated with an increased risk of amyloidosis in FMF patients, especially in patients homozygous for M694V, whereas the MICA (Major Histocompatibility Complex, MHC class-I-chain-related type A) gene seems to have an effect on disease course but not its clinical manifestations. The most effective treatment for FMF patients is colchicine, which should be taken regularly on a life-long basis. It decreases the frequency and severity of crises and prevents renal amyloidosis.