This deficient mechanism is probably located at the level of the B30.2 domain (exon 10) where most of the pathogenic mutations associated with FMF are located. It is probably the interaction of this domain with the cytoskeleton (microtubules) 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 (e.g. joints or the peritoneal cavity). 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 (MPT)", 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.
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.