FMF is an autoinflammatory disease inherited in an autosomal recessive pattern. It is characterized by recurrent self-limiting attacks of fever and abdominal pain that can be accompanied by polyserositis, arthritis and erysipelas-like erythema (ELE).1 In 90% of cases, the disease onset is during childhood, with 65% of patients being under 10 years old.2 FMF is especially common among Turks, Arabs, Sephardic Jews and Armenians.3 FMF originates from mutations in the MEFV gene.4 Encoded by the MEFV gene, the protein pyrin regulates the inflammatory response. Gain-of-function mutations in this gene lead to a prolonged inflammatory response and an overload of interleukin-1β.5 Over 400 MEFV mutations have been identified worldwide, affecting exons 2, 3, 5 and 10. While the distribution and type of these mutations vary by ethnicity, the most common variants in Turkey are the M694V, M680I and V726A in Exon 10 and the R202Q and E148Q in Exon 2.6,7

Due to the genetic and demographic differences, patients often present with a wide variety of symptoms.8 The abdominal pain, caused by peritonitis, can be misdiagnosed as an acute appendicitis especially with the accompanying fever reaching 40°C. Additionally, ongoing inflammation of the pleura and pericardium can lead to shortness of breath and mimic cardiac pathologies.9 These symptoms are often exacerbated during attacks, while patients may present a milder picture or even be asymptomatic during attack-free periods. However, acute phase reactants like CRP can remain elevated during attack-free periods. This indicates an ongoing inflammatory process and underscores the need for regular treatment, mainly with colchicine. In case of a treatment delay, patients may develop secondary amyloidosis, which could lead to renal failure and significantly worsen the prognosis.1,10 Patients that carry some specific variants of MEFV mutations, such as the homozygous M694V mutation on Exon 10, are more prone to developing secondary amyloidosis and should be closely monitored.11,12

Descriptions of FMF frequently based on the phenotypes of patients carrying Exon 10 mutations, often overlooking atypical presentations such as musculoskeletal findings, various forms of vasculitis, and neurologic manifestations.13 Approximately half of FMF patients experience musculoskeletal symptoms, with arthralgia and arthritis being the most common presentations, typically manifesting as recurrent monoarthritis in the large joints of the lower extremities. Non-specific myalgia and fatigue can also be present during attacks.14–16 Genotype-phenotype correlations for these atypical symptoms of FMF remain unclear.8

Although the role of Exon 10 mutations in FMF is well established, as these variants are closely associated with severe and classical disease phenotypes, the impact of common Exon 2 mutations like R202Q and E148Q on the disease is not as clearly defined regarding their pathogenic and modulatory significance.6 E148Q and R202Q are among the most prevalent MEFV variants in the general population and are often categorized as variants of uncertain significance (VUS).3,7 Nonetheless, emerging evidence indicates that these variants may influence the clinical spectrum of FMF by modulating inflammatory activity or contributing to milder or atypical disease courses.6,8 Given their high frequency and unclear pathogenic potential, the analysis of Exon 2 mutations provides a valuable opportunity to determine whether these variants act merely as benign polymorphisms or exert a subtle influence on the clinical expression of FMF.7,8

In this study, we aimed to analyze the clinical features of patients who carry the Exon 2 mutations (E148Q and R202Q) and compared the features of this group with patients carrying Exon 10 mutations, hoping to uncover the clinical implications of different variants.

This retrospective, single-center case–control study was conducted at the Rheumatology Department of Istanbul University-Cerrahpaşa, a tertiary university hospital, between 2009 and 2019. The study population consisted of adult patients aged 18 years or older who had been diagnosed with FMF according to the Tel-Hashomer diagnostic criteria.17 All patients had a confirmed MEFV gene analysis, performed in the same institutional genetics laboratory by direct DNA sequencing.

41 patients carrying Exon 2 mutations were included in the study. Among them, 25 patients had only the E148Q mutation (3 homozygous and 21 heterozygous), 12 had only the R202Q mutation (all heterozygous), and 5 carried the compound heterozygous E148Q+R202Q combination. In the exon 10 mutation group (n=57), 38 patients carried the M694V mutation (20 homozygous and 18 heterozygous), and 19 were compound heterozygous, carrying M694V together with another exon 10 variant. The distribution of MEFV mutations across groups is presented in Table 1.

The number of women was higher in both groups. 78.0% of the exon 2 group and 63.2% of the exon 10 group were female. No significant differences were observed between the groups in terms of gender distribution (p=0.127). The average age of symptom onset of patients in the exon 2 group was 19.50 (95% CI, 13.50–43.00) years, while the average age of symptom onset of patients in the exon 10 group was 8.00 (95% CI, 5.00–16.00) years. Patients in the exon 10 group began to show symptoms 11.50 years earlier. A significant difference was observed between the average age of symptom onset of the patients (p<0.001). The delay in diagnosis was 6.00 (95% CI, 1.00–11.00) years in patients in the exon 2 group, while it was 4.00 (95% CI, 1.00–13.00) years in patients in the exon 10 group (p=0.866). The demographic characteristics of both groups are shown in Table 2.

Typical symptoms such as fever and abdominal pain were observed more in the exon 10 group. While fever was seen in 56.1% of the patients in the exon 2 group, it was seen in 77.2% of the patients in the exon 10 group (p=0.030). Although abdominal pain was seen in 68.3% of the patients in the exon 2 group, it was observed in 89.5% of the patients in the exon 10 group (p=0.018).

Symptoms affecting the musculoskeletal system, such as arthralgia and myalgia, were more frequent in exon 2 mutations. While arthralgia was seen in 73.2% of the patients in the exon 2 group, it was observed in 56.1% of the patients in the exon 10 group (p=0.004). Myalgia was reported in 24.4% of the patients in the exon 2 group, it was noted in 5.3% of the patients in the exon 10 group (p=0.013). The frequency of chest pain, arthritis, and ELE was similar in both groups, with no significant differences found. The p-values were 0.255, 0.115, and 0.447, respectively. Amyloidosis developed in two patients in each group (p=1.000).

In the exon 2 group, 25.0% of patients had a family history of FMF, whereas in the exon 10 group, 72.2% had a family history of FMF. The presence of a family history was significantly higher in the exon 10 group (p<0.001).

All patients in both groups had received colchicine during their course of treatment. While the colchicine response was 91.7% in the exon 2 group, the colchicine response was 96.4% in the exon 10 group. There were no significant differences between the groups in terms of response to colchicine (p=0.376). Clinical characteristics, colchicine responses and family histories of both groups are shown in Table 2.

In the univariate model, presented in Table 3, later age at symptom onset (OR=0.96, 95% CI 0.94–0.99, p=0.004), lower frequency of abdominal pain (OR=3.94, 95% CI 1.35–11.52, p=0.012), and lower prevalence of fever (OR=2.65, 95% CI 1.10–6.35, p=0.029) were found to be associated with Exon 2 mutation status. Musculoskeletal findings were particularly relevant, as arthralgia (OR=0.29, 95% CI 0.12–0.68, p=0.005) and myalgia (OR=0.17, 95% CI 0.04–0.67, p=0.011) showed significant associations. Additionally, family history of FMF was strongly linked to Exon 10 mutations rather than Exon 2 (OR=8.68, 95% CI 3.44–21.89, p<0.001).

In the multivariate analysis, illustrated as Table 4, independent predictors of Exon 2 mutation status were age at symptom onset (OR=0.96, 95% CI 0.93–0.99, p=0.012), and family history (OR=11.42, 95% CI 3.60–36.24, p<0.001).

This study aimed to explore the clinical impact of MEFV Exon 2 variants (E148Q and R202Q) by comparing their phenotypic features with those of Exon 10 mutations in patients with Familial Mediterranean Fever (FMF). By doing so, we sought to clarify whether these common Exon 2 variants, often regarded as variants of uncertain significance and whose roles in FMF are not fully understood, influence the clinical spectrum or represent benign polymorphisms.

In this study, we showed that FMF patients with exon 2 mutations frequently exhibit atypical symptoms, including arthralgia and myalgia, and display fewer typic symptoms like abdominal pain and fever than those with exon 10 mutations. Family history was less common in exon 2 cases, and patients with exon 2 mutations experienced a later age at symptom onset compared to those with exon 10 mutations. Although E148Q and R202Q mutations have distinct clinical features, exon 2 variants should not be considered a separate clinical category in FMF.

According to the INFEVERS database, there are more than 400 mutations reported in the MEFV gene to date, but the significance of many of these mutations in the pathophysiology of FMF remains unknown.18 Different mutations are believed to result in varying clinical outcomes and to reflect this, mutations are classified as benign, probably benign, uncertain significance, possibly pathogenic, or pathogenic.19 While the relationship between Exon 10 mutations and FMF has been demonstrated well, the role of Exon 2 mutations such as R202Q and E148Q in the development of FMF still remains unclear. In Tufan et al.’s study, a consensus has not yet been reached to classify the E148Q variant as benign or pathogenic and the E148Q variant has been subsequently listed as a variant of uncertain significance (VUS) due to its unclear clinical association.10 On the other hand, Migita et al. have defined the E148Q variant as a mutation that causes low-severity disease.20 The R202Q variant is generally considered a polymorphism and it is also commonly found positive in the healthy population.21 However, Türkuçar et al. reported that R202Q may cause typical FMF findings, similar to patients with Exon 10 mutation.6 As R202Q is not considered a pathogenic variant, it may contribute to a FMF-like disease rather than directly causing FMF.

Among the 41 patients with exon 2 mutations and the 57 patients with exon 10 mutations, no significant differences were observed in gender (p=0.127), or delay in diagnosis (p=0.866). However, a significant difference was found in the age of symptom onset (p<0.001), with symptoms of patients carrying the exon 10 mutation beginning 11.50 years earlier. To further clarify these associations, univariate and multivariate logistic regression analyses were conducted. The models confirmed that later age at symptom onset was an independent predictor of Exon 2 mutation status. These findings suggest that Exon 2 variants may be linked to a milder, musculoskeletal-dominant disease pattern rather than the classical systemic presentation observed in Exon 10 carriers. Our findings were further supported by the study conducted by Dundar et al., who also reported that the onset of symptoms in pediatric patients with exon 10 mutations were significantly lower than non-exon 10 mutations.22

When examining the clinical presentations between the groups, the comparison between the exon 2 and exon 10 groups revealed no significant differences in the rates of chest pain, arthritis, ELE. In contrast, according to Yıldırım et al., M694V homozygous mutations are more frequently observed in patients with ELE and these individuals are more likely to experience arthritis, requiring higher doses of colchicine due to the severe course of the disease.23 Çakmak et al. further reported that ELE is significantly linked to a more severe clinical phenotype of FMF, with a notable association to M694V homozygosity and an increased risk of developing amyloidosis.24

Typical symptoms such as fever and abdominal pain were significantly more common in the exon 10 group, while atypical symptoms affecting the musculoskeletal system, such as arthralgia and myalgia, were significantly more frequent in patients with exon 2 mutations. According to the findings of Bilge et al., the presence of fever was similar in both groups. Although Bilge et al. studied a larger cohort than ours, we believe that fever, being a key symptom that prompts patients to seek medical attention, should be more prevalent in the group with an earlier diagnosis, specifically, those with exon 10 mutations.25 Aydın et al. observed a significant difference in the frequency of fever in the early onset patient group, which mostly consisted of patients with M694V mutation. In this group, 81.7% of patients reported febrile attacks. This finding underscores the relevance of fever as a prominent symptom in early-onset FMF, particularly in patients carrying the M694V mutation.

In a study conducted by Comak et al., the frequency of abdominal pain was significantly lower in patients with the R202Q mutation, and the frequency of arthralgia and myalgia was higher, although statistically insignificant.26 A study by Avcı et al. found that in patients with exon 2 mutations, the presence of exon 10 mutations was associated with a marked difference in the frequency of arthralgia, with 26.8% of patients with exon 10 mutations experiencing this symptom compared to 89.7% in those without exon 10 mutations. Nevertheless, this difference did not achieve statistical significance.27 These findings suggest that exon 10 mutations might have a protective effect against arthralgia in individuals with exon 2 mutations, although further research with larger sample sizes is needed to confirm this potential link.

The prevalence of family history was significantly higher in the exon 10 group (p<0.001). In the study by Avcı et al., among patients with exon 2 mutations, the inclusion of exon 10 mutations was associated with an increase in the family history of FMF, although this increase was not statistically significant.27 This finding suggests that exon 10 mutations, such as M694V, are associated with a stronger hereditary component of the disease and are more likely to have a pronounced impact on the phenotype. This association was also reflected in the multivariate regression, where positive family history remained a strong independent predictor of Exon 10 mutation status.

Secondary amyloidosis developed in two patients in each group, and no significant differences were found between the groups. Even though factors such as family history and treatment delays were considered, the comparison of amyloidosis prevalence between patient groups in this case–control study could be significantly influenced by compliance to treatment and small sample size. Previous studies have found a correlation between the M694V mutation and FMF-associated amyloidosis.28 A cohort study with a larger, regularly monitored patient group would likely yield more accurate data.

In examining the effect of MEFV gene mutations on the response to colchicine, no significant differences were found between the groups (p=0.236). Aydin O. et al. reported no differences in colchicine response when comparing patients with the M694V mutation to those without it, and our study observed similar results.29

Our analysis showed that patients with exon 2 mutations more often presented with atypical clinical features, such as arthralgia and myalgia, and typically fewer systemic findings compared with those carrying exon 10 mutations. Additionally, patients with exon 2 variants were older at disease onset and less likely to report a positive family history of FMF. These observations suggest that exon 2 mutations should be considered within the broader clinical spectrum of FMF rather than as a distinct category.

While our findings do not support classifying exon 2 variants as clinically defining mutations, they may still exert a modulatory effect on disease expression. Specifically, E148Q and R202Q variants, though often considered variants of uncertain significance or common polymorphisms, may contribute to atypical or milder FMF manifestations, and their potential clinical impact cannot yet be excluded.

In conclusion, this study underscores the heterogeneous and evolving nature of FMF, emphasizing the need for a personalized approach to patient evaluation and management. Future research should focus on larger, prospective, multicenter cohorts to validate these findings and better delineate the role of exon 2 variants in FMF pathogenesis.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

None.