Familial Mediterranean fever is no longer a rare disease in Japan

The study was conducted at the Clinical Research Center of Nagasaki Medical Center, Japan. Patients with unexplained fever were recruited consecutively from those treated and followed up in the rheumatology department of participating hospitals. Unexplained fever was defined as a temperature above 38 °C that lasts for 3 weeks including recurrent episodes of fever without diagnosis after standardized history-taking, physical examination, and obligatory investigation. These subjects included the newly diagnosed FMF patients in the previously performed multi-centric survey for FMF [12]. The study comprised 601 patients (216 males, 385 females, mean age 44.3 ± 20.2 years). On the basis of Tel Hashomer criteria [13], patients were divided into three groups: sure FMF—certain clinical diagnosis in the presence of two major criteria or one major and two minor criteria; probable FMF—clinical diagnosis considered probable in the presence of one major and one minor criterion or two minor criteria; and non-FMF—clinical diagnosis considered unlikely in the presence of only one minor and no major criteria. Clinical manifestations of FMF, including characteristics of febrile episodes (duration and frequency), and the presence of serositis (chest or abdominal pain), arthritis, myalgia, and erysipelas-like rash was documented. Demographic data (including gender, consanguinity of parents, familial history, and age of onset of inflammation signs) and main clinical data (including fever, thoracic, abdominal, articular, cutaneous signs, duration and frequency of episodes, presence of amyloidosis, and response to colchicine) were recorded by the doctor using a standard form. Response to colchicine was defined as complete, incomplete, or absent.

Blood samples (2 ml) were collected from all subjects. Genomic DNA was extracted from whole blood using the Wizard® Genomic DNA Purification Kit (Promega, USA). Mutational analysis was performed by direct DNA sequencing. Polymerase chain reaction (PCR) amplification was performed for each MEFV exon, as described previously [9]. A total of 27 PCR products per patient were purified using ExoSAP-IT (GE Healthcare Japan, Tokyo, Japan) and sequenced directly using specific primers and BigDye Terminator v1.1 (Applied Biosystems, Tokyo, Japan). The control group for MEFV genotyping consisted of 105 gender-matched Japanese healthy subjects (44 men and 61 women). The mean ± SD age was 44.2 ± 11.5 years.

Data were analyzed using SPSS software (SPSS Inc., Chicago, IL, USA). Results were expressed as the mean ± standard deviation (SD) for continuous variables. For quantitative data, the Mann–Whitney U rank-sum test compared two independent groups. Comparisons for categorical variables were evaluated using the chi-square test (or Fisher’s exact test when appropriate). Adjustment for multiple comparisons was performed using the Bonferroni method. Pc values were calculated by multiplying the p value by the number of alleles tested.

Ten patients were excluded from the study (Fig. 1). The main reasons for exclusion were the absence of periodic fever syndrome (drug fever, infections, and neoplastic diseases). At the time of analysis, the mean patient age was 44.3 ± 20.2 years (range 0–94 years) and the mean age of the onset of symptoms was 36.3 ± 19.7 years (range 1–94 years). The main clinical characteristics of the 601 patients were as follows: 385 patients were female (64.1 %), fever was observed in 482 (80.2 %), abdominal symptoms in 163 (27.1 %), thoracic signs in 75 (12.5 %), arthritis signs in 345 (57.4 %), and amyloidosis in 22 (3.7 %). On the basis of Tel Hashomer criteria, 192 patients (31.9 %) were diagnosed with FMF, of whom 108 had typical FMF (56.3 %) and 84 had incomplete FMF (43.7 %). The remaining 409 patients (68.1 %) were classified as non-FMF patients, including two patients with suspected tumor necrosis factor receptor associated periodic syndrome (TRAPS) and two patients with periodic fever, aphthous stomatitis, pharyngitis, and adenitis syndrome (PFAPA) (Fig. 1). As shown in Fig. 1, among non-FMF patients, 118 patients had established rheumatic diseases (rheumatoid arthritis, n = 35; systemic lupus erythematosus, n = 19; Behçet's disease, n = 17; gout, n = 12; inflammatory myopathies, n = 7; mixed connective-tissue disease, n = 4; psoriatic arthritis, n = 4; remitting seronegative symmetrical synovitis with pitting edema, n = 3; Henoch-Schonlein purpura, n = 3; vasculitis syndrome, n = 3; SAPHO syndrome, n = 2; palindromic rheumatism, n = 2; Sjögren's syndrome, n = 2; Reiter's syndrome, n = 1; Crowned dens syndrome, n = 1; relapsing polychondritis, n = 1; spondylarthritis, n = 1; systemic sclerosis, n = 1). Additionally, among non-FMF patients, 68 patients were finally diagnosed as having rheumatic diseases (Behçet's disease, n = 11; rheumatoid arthritis, n = 9; inflammatory myopathies, n = 7; vasculitis syndrome, n = 7; Sjögren's syndrome, n = 6; systemic lupus erythematosus, n = 6; palindromic rheumatism, n = 5; mixed connective-tissue disease, n = 4; gout, n = 3; CREST syndrome, n = 2; ankylosing spondylitis, n = 2; adult onset Still's disease, n = 1; Caplan's syndrome, n = 1; IgG4-related disease, n = 1; SAPHO syndrome, n = 1; psoriatic arthritis, n = 1; eosinophilic fasciitis, n = 1). Among the remaining non-FMF patients, 37 patients were finally diagnosed with non-rheumatic diseases (amyloidosis, n = 5; myelodysplastic syndromes, n = 4; Castleman's disease, n = 4; undifferentiated arthritis, n = 3; viral infection, n = 3; Sweet's disease, n = 2; Kikuchi's disease, n = 2; hemophagocytic syndrome, n = 2; chronic thyroiditis, n = 2; idiopathic thrombocytopenic purpura, n = 1; alcoholic hepatitis, n = 1; Wilson's disease, n = 1; cryoglobulinemia, n = 1; Crohn's disease, n = 1; recurrent stomatitis, n = 1; malignant lymphoma, n = 1; reactive lymphadenitis, n = 1; non-tuberculous mycobacterial disease, n = 1; interstitial nephritis, n = 1).

FMF patients had a shorter duration of febrile attack and higher frequencies of abdominal or thoracic symptoms and family history of periodic fever (Table 1). Colchicine was administered to 300 patients (sure FMF, 86.1 %; probable FMF, 95.2 %; non-FMF patients, 31.1 %), and the response was higher in patients with typical FMF (97.8 %) compared with those in the other groups (non-FMF, 64.6 %). The response rates for colchicine treatment were not significantly different between subgroups of FMF classified by MEFV mutations (Table 2).

As shown in Table 3, short durations of fever, and thoracic and abdominal symptoms were more frequently observed in sure FMF patients (2.2 ± 0.8 days) compared with probable FMF patients (6.2 ± 5.5 days). Conversely, arthritis was more frequently observed in probable FMF patients compared with sure FMF patients. Among FMF patients, 7 (3.6 %) had biopsy-proven amyloid A (AA) amyloidosis (sure FMF, n = 6; probable FMF, n = 1). Among non-FMF patients, 15 patients had AA amyloidosis and primary diseases were rheumatoid arthritis (n = 10) and Crohn's disease (n = 1), whereas primary diseases were not identified in four patients. The allele frequencies of MEFV mutations between AA amyloidosis patients with or without FMF are shown in Table 4. Only the allelic frequency of M694I was significantly higher in FMF patients with AA amyloidosis.

For the sure FMF patients, 13.0 % (14/108) had concomitant rheumatic diseases (rheumatoid arthritis, n = 6; Sjögren's syndrome, n = 3; dermatomyositis complex, n = 2; Behçet's disease, n = 1; adult onset Still's disease, n = 1; Kawasaki disease, n = 1). In the probable FMF patients, 14.3 % (12/84) had concomitant rheumatic diseases (systemic lupus erythematosus, n = 4; Sjögren's syndrome, n = 3; rheumatoid arthritis, n = 2; Behçet's disease, n = 1; palindromic rheumatism, n = 1; polymyositis, n = 1).

FMF patients with rheumatic diseases had a higher frequency of arthritis episodes and an elderly onset of FMF. Conversely, FMF patients without rheumatic diseases had a higher frequency of abdominal pain and family history of FMF (Table 5). No significant difference was observed in the allele frequencies in MEFV mutations between FMF patients with or without rheumatic diseases (Table 6).

Distributions of MEFV genotypes in the FMF and non-FMF groups are shown in Table 7. Table 8 shows the allelic frequencies of MEFV mutations in the FMF and non-FMF groups. Most FMF patients (94.3 %, 181/192) carried at least one MEFV mutation. Significant differences were observed between FMF patients and healthy subjects regarding the allelic frequencies of mutations in MEFV exon 2 (E148Q, 39.1 % vs 24.8 %, respectively) and exon 10 (M694I, 13.5 % vs 0 %, respectively). However, there were no significant differences between FMF patients and healthy subjects regarding the allelic frequencies of other mutations (Table 9).

Table 10 shows the allelic frequencies of MEFV mutations according to the FMF disease phenotype. Among FMF patients, the allelic frequencies of the MEFV exon 10 mutation (M694I) were significantly higher in sure FMF patients compared with probable FMF patients, while the allelic frequencies of the MEFV exon 3 mutations (P369S, R408Q) were significantly lower in sure FMF patients compared with probable FMF patients. No significant difference was seen in the allele frequencies of other MEFV mutations between FMF patients with or without rheumatic disease.

Although FMF is considered an autosomal recessive disease, the presence of only a single mutation can often be associated with the occurrence of FMF. We analyzed the differences in clinical manifestations according to the number of MEFV mutations. FMF patients with two or more than two MEFV mutations had AA amyloidosis and family history of periodic fever more frequently compared with those with a single or no MEFV mutations (Table 11).