Assessment of pyrin gene mutations in Turks with familial Mediterranean fever (FMF)

Association of FMF-Related (MEFV) Point Mutations with Secondary and FMF Amyloidosis

BACKGROUND

Familial Mediterranean fever (FMF) is the major cause of AA amyloidosis in Turkey. M694V mutation in MEFV gene was suggested to be associated with severe clinical features and amyloidosis of FMF.

METHODS

In this study, the frequencies of three FMF-related MEFV mutations (M694V, M680I and V726A) were investigated in FMF patients with (AA-FMF, n = 37) and without amyloidosis (non-AA-FMF, n = 35), in patients with secondary amyloidosis related to non-FMF inflammatory conditions (S-AA, n = 19) and in a non-inflammatory control group (n = 185) by molecular genetic studies using polymerase chain reaction with the ARMS (amplification refractory mutation system) method.

RESULTS

Both AA and non-AA-FMF patients had significantly higher MEFV mutations compared to non-inflammatory controls (81 and 62.7% respectively vs. 4.2%, p = 0.0001). AA-FMF patients carried significantly more MEFV mutations than non-AA-FMF patients (p = 0.01). M694V was the most common mutation in both FMF groups (63.5 vs. 51.4%), however allele frequency (p = 0.17) and the number of homozygous patients for this mutation did not differ between the groups (p = 0.77). Although lower compared to FMF patients, S-AA patients also had a significantly higher incidence of MEFV mutations than non-inflammatory controls (21 vs. 4.2%) (p = 0.0002). M694V was the only MEFV mutation in this group.

CONCLUSION

MEFV mutations are found to be increased both in FMF and non-FMF associated secondary amyloidosis in our study; however, no clear association between M694V and amyloidosis is observed, except in the non-FMF group. Our results suggest that MEVF mutations may also serve as a severity marker for other inflammatory conditions.

MEFV mutations in multiplex families with familial Mediterranean fever: is a particular genotype necessary for amyloidosis?

Familial Mediterranean fever (FMF) is an autosomal recessive disease. It is characterized by recurrent febrile episodes in association with peritonitis, pleuritis, and arthritis. Progressive systemic amyloidosis is the most important complication of FMF that inevitably leads to chronic renal failure. Recently, the gene for FMF, MEFV, has been cloned and four missense mutations have been described: M694V, M680I, V726A, and M694I. Initial studies have suggested that the presence of the M694V mutation carries a significant risk for the development of amyloidosis. In this study, we present seven families, in which at least two individuals have been diagnosed with FMF and at least one with amyloidosis. Among 18 individuals, in whom molecular testing was performed for the four aforementioned mutations, ten had amyloidosis. None of these ten individuals was found to be homozygous for the M694V mutation. In three families, there were two sibs with amyloidosis. None of the sib-pairs with amyloidosis was found to have the same genotype. There were two or more sibs with the same genotype in four families. Only one sib from each family developed amyloidosis in these families. These results provide evidence that FMF patients without the M694V mutation are also at risk for the development of amyloidosis. Particular mutations themselves do not appear to be sufficient to explain the occurrence of amyloidosis in all cases with FMF.

The familial mediterranean fever protein interacts and colocalizes with a putative Golgi transporter

The biological function of pyrin, the protein mutated in Familial Mediterranean Fever (FMF), has not been elucidated. Based on sequence homology, a transcription factor activity was proposed for this neutrophil-specific protein. In a yeast two-hybrid assay, neither transcription activation activity nor any self interaction was detected for pyrin. Screening of an expression cDNA library of peripheral blood leukocytes using as bait the carboxyl portion of pyrin (amino acids 557-781), which contains most of the FMF mutations, led to the identification of P/M-IP1 (pyrin/marenostrin interacting protein 1). A splice variant of P/M-IP1, GTC-90, had previously been described as a component of the 13S hetero-oligomeric protein complex that stimulates in vitro Golgi transport. We have now shown that P/M-IP1 colocalizes with pyrin in the perinuclear cytoplasm of Cos-7 cells and that the interaction between these two proteins is impaired by FMF causing mutations in pyrin. These data suggest that, at some stage of its functional pathway, pyrin resides in the cytoplasm and might be involved in, or impacted by, cellular protein sorting by the Golgi apparatus. The data also imply that P/M-IP1 may be involved in the abnormal inflammatory response that occurs in patients with FMF.