Metabolic syndrome among Egyptian children with Familial Mediterranean Fever: a case–control study

Background Familial Mediterranean fever (FMF) is the most prevalent inherited autoinflammatory disease globally. Metabolic syndrome (MetS) is a cluster of interrelated risk factors; insulin resistance, obesity, dyslipidemia, and hyper‑ tension are the main constituents of MetS. Aim This study aimed to investigate components of metabolic syndrome among Egyptian children with FMF dur‑ ing the attack‑free period. Patients and methods This is a case–control study that was conducted in the Pediatric Rheumatology Outpatient Clinic and Pediatric Endocrinology Clinic, Children’s Hospital, Faculty of Medicine, Cairo University. It was conducted on 40 patients with FMF. The patients included were of both sexes and aged 10 years or older, during the FMF attack‑ free period; they were compared to 40 apparently healthy age‑ and sex‑matched children as controls. All subjects in this study were subjected to detailed history taking, anthropometric measurements, general and systemic exami‑ nations. Laboratory evaluation (at the time of the study) was done at time of study, in the form of CBC with differen‑ tial, BUN, creatinine, ESR, serum amyloid A, urine analysis, serum insulin, fasting blood glucose, and lipid profile. FMF gene mutations were collected from patients’ files. Results The mean ± SD age of FMF patients was 12.65 ± 1.82 (10–17) years, while the mean ± SD age of the con‑ trol group was 12.6 ± 1.82 (10–16) years. Among FMF patients, 50% were males, and 50% were females (F:M = 1:1), while in the control group, 47.5% were females, and 52.5% were males. All FMF patients were during the attack‑free period. There was a statistically significant difference between both groups regarding insulin resistance, being more frequent among the FMF patients’ group, with a p ‑value of 0.025. Conclusion None of our FMF patients met the criteria for the definition of metabolic syndrome, but there was a sig‑ nificant difference between cases and control regarding insulin resistance with higher frequency among FMF patients, probably due to the ongoing subclinical inflammation. This indicates that children with FMF may be at a higher risk of getting metabolic syndrome later on in life.


Background
FMF is the predominant inherited periodic fever and monogenic autoinflammatory disease in the world [1].FMF is prevalent in countries around the Mediterranean area, but it is becoming more widely known worldwide [2].FMF is an autosomal recessive disease related to mutations in the Mediterranean fever gene (MEFV) [2].
Pyrin, which is encoded by MEFV, is a component of the NLRP3 inflammasome complex and regulates the production of the pro-inflammatory cytokine interleukin-1β (IL-1β) [3].
FMF is described by recurrent episodes of fever and a variety of clinical symptoms, including arthritis, chest pain, and abdominal pain, which are caused by inflammation of the serous membranes.Episodes are self-limiting.Amyloidosis and renal failure might arise as complications of the condition [4].Although the course of the disease has been improved by treatment with colchicine, persistent subclinical inflammation may eventually result in endothelial dysfunction and atherosclerosis [2].
Metabolic syndrome (MetS) is defined by a cluster of several cardio-metabolic risk factors, specifically visceral obesity, dyslipidemia, hypertension, and impaired glucose metabolism, which, when combined, raise the chance of acquiring type 2 diabetes mellitus and cardiovascular disease (CVD) in the future [5].Various classifications have been proposed in the literature in order to define pediatric MetS.The majority are based on the adult MetS categories.Nonetheless, it is mandatory in pediatrics to employ pediatric criteria and age-and sex-specific percentiles [5].Due to an increased release of inflammatory markers (e.g., IL-1β, TNF-α) in FMF patients, it is thought that a mutation in the MEFV gene could increase the prevalence of metabolic syndrome among these patients.To our knowledge, the frequency of MetS in children with FMF has not been studied before.This study aims to investigate the frequency of MetS in children with FMF.

Methods
This case-control study was conducted in the Pediatric Rheumatology Outpatient Clinic and Pediatric Endocrinology Outpatient Clinic, Children's Hospital, Faculty of Medicine, Cairo University.It was conducted in 40 patients with FMF, who were diagnosed according to the new pediatric criteria for FMF (Yalcınkayaetal., 2009) [6], and 40 age-and sex-matched healthy children as a control group.The patients included were of both sexes, above the age of 10 years, and were during the attackfree period (at least 2 weeks free from the end of the last attack).Patients with other rheumatological, endocrinal disorders or any other chronic diseases were excluded.Also, FMF patients who were on steroids were excluded from our study.All FMF patients were subjected to detailed history taking (including age at onset of FMF, age at diagnosis, disease duration, FMF manifestations during the disease course, dose and duration of colchicine administration, compliance, and response to colchicine).Assessment of FMF disease severity was identified by the international severity scoring system for FMF (ISSF) (Demirkaya et al., 2016) [7].The response of colchicine was evaluated according to the FMF 50 score [8].Height (cm), weight (kg), body mass index (BMI = weight (kg)/[height (m 2 ], and waist circumference were obtained for both FMF patients and the control group according to standardized equipment and following the recommendations of the World Health Organization (WHO).Each child's physical growth was evaluated by calculating their weight, height, and BMI standard deviation scores (SDS) using the Egyptian growth reference data and the percentiles of all anthropometric measurements.A full general and systemic examination was done.Laboratory investigations were done at the study time for both cases and the control group, including complete blood picture, ESR, BUN, creatinine, serum insulin, fasting blood glucose, triglycerides, LDL, HDL, and total cholesterol.Urine analysis and serum amyloid A (SAA) were done for FMF patients.MEFV gene mutations were collected from patients' files.The evaluation of the existence of metabolic syndrome was according to IDF (International Diabetes Federation) criteria in children and adolescents aged 10 to 16 years.Abdominal obesity, assessed by waist circumference, is the essential criterion for diagnosis of metabolic syndrome; it is defined by waist circumference ≥ 90th percentile for age and sex.The diagnosis of metabolic syndrome was made in the presence of abdominal obesity associated with two of the following criteria: Insulin resistance was calculated for both groups using the homeostasis model assessment for insulin resistance (HOMA-IR).The formula for HOMA-IR is the product of the glucose and insulin levels divided by a constant, calculated by using the following formula: fasting glucose (mg/dL) × fasting insulin (µU/mL)/405 [10], and insulin resistance is indicated by a number higher than 2 [11].Patients were recruited from November 2022 to January 2023.

Ethical approval
The Ethical Committee of the Faculty of Medicine, Cairo University, in Egypt, approved the study.The approval code from the ethical committee is MS-417-2020.The aims, procedures, and potential advantages of the study were deliberated upon with caregivers of all study participants or their children older than 12 years.All participants were enrolled after receiving their caregivers' informed consent.

Statistical analysis
Data was subjected to computer-assisted statistical analysis using SPSS (Statistical Package for Social Science) version 22. Categorical variables were expressed as frequency and percentage and compared using chi-square.Continuous variables were expressed as mean ± standard deviation and will be compared using the t-test.Nonparametric data (median and interquartile range) was expressed and compared using the Mann-Whitney U-test.Association between continuous variables was tested using Pearson correlation.A p-value ≤ 0.05 was considered significant.

Results
The clinical, biochemical findings and demographics of both groups are shown in Table 1.There was no significant difference in age and sex between both cases and control groups, with p-values = 0.903 and 0.823, respectively.There was a statistically significant difference between both groups regarding insulin resistance, which was higher among the patients' group, p-value = 0.025.
Laboratory evaluation of the patients and controls showed statistically significant differences regarding ESR and HDL levels, which were higher in the FMF group with p-values of 0.04 and 0.001, respectively.In contrast, LDL levels were lower in FMF patients than in the control group, with p-value = 0.000.
Comparing anthropometric measurements between both groups, we observed statistically significant differences in the height and waist circumference percentiles.Both were higher in the control group than in the patients' group.
As regards the characteristics of disease in FMF patients, the following results were obtained (Table 2).
Among the group, 33 (82.5%) had a positive family history of FMF.The most common clinical presentations in FMF patients during illness were abdominal pain in 11 (27.5%)patients, chest pain in 9 (22.5%)patients, fever in 7 (17.5%)patients, and arthralgia in 7 (17.5%)patients.A total of 77.5% (31) of patients in our FMF cases had heterozygous genotypes, 15% (6) patients had homozygous genotypes, and 7.5% (3) patients had compound heterozygous genotypes.The most frequent MEFV gene mutations were V726A in seven cases (17.5%) and M6941 in six (15%) cases.Regarding the FMF disease severity score, mild disease was found in 11 patients (27.5%).Moderate disease was found in 18 patients (45%), and severe disease was found in 11 patients (27.5%).Mean of serum amyloid A (SAA) among our FMF patients was 82.78 ± 50.68 mg/dL.Insulin resistance was detected among all FMF patients with the compound heterozygous MEFV gene mutation, followed by the heterozygous gene mutation, and, lastly, the homozygous mutation with the following frequencies: 100%, 64.5%, and 16.7%, respectively, as shown in Table 3.

Discussion
FMF is the most pronounced auto-inflammatory syndrome in children, marked by recurring episodes of fever and serositis.Childhood obesity has been steadily rising over the past few years, and in developed nations, it is the most common nutritional issue.Metabolic syndrome (MetS) is often related to obesity.Research has demonstrated that a critical factor in the development of MetS is insulin resistance (IR), and that there is a high incidence of IR in patients with FMF.Studies that analyze this possible association in children are scarce.The majority of the research that we could find focused on adults.Our case-control observational study included 40 children with FMF, compared to 40 apparently healthy age-and sex-matched children as a control group.There was a statistically significant difference between FMF patients and control groups as regards insulin resistance, where 60% of FMF patients had insulin resistance.
In comparison, 35% of the control group had insulin resistance, and this suggests that these children were susceptible to subsequently acquiring metabolic syndrome.Congruent with our findings, Sarkis et al. [12] also found that insulin resistance was more common in FMF patients than in the control group.Ugurlu et al. [13], Candan et al. [14], and Dursun et al. [15] found no insulin resistance in both groups.These studies were in adults; no further studies are available in the pediatric population.The frequency of IR among our FMF patients was greater than the prevalence rates of IR observed in population-based studies involving children and adolescents, which ranged between 3.1 and 44% [16].IR detected among our patients may be related to chronic inflammation and persistent subclinical inflammation, and it may be associated with the age of our cases as we selected children above the age of 10 years, which are in the prepubertal stage, which includes hormonal changes that increase the possibility of insulin resistance.Chronic subclinical inflammation is also considered a component of IR [17].Pickup and Crook [18] discussed that chronic inflammation could potentially serve as a precipitating element in the development of IR and, ultimately, type 2 diabetes.
Insulin resistance is identified as the compromised biological response of target tissues upon stimulation with insulin.Insulin-receptor-containing tissues can all develop resistance to insulin.However, the liver, skeletal muscle, and adipose tissue are the primary tissues responsible for insulin resistance.Resistance to insulin impairs glucose elimination, causing hyperinsulinemia and increased beta-cell insulin production as a compensatory mechanism [19].Normal-weight children may also be impacted by IR, even though it is more frequently associated with obesity, indicating that elevated adiposity does not exclusively serve as its determinant [20].
In our study, sex distribution in FMF patients was 1:1, similar to Egyptian research by Marzouk et al. [2].The mean age of FMF patients at the time of the study was 12.65 ± 1.82 years, and the mean age at the disease onset was 6 years.The mean age at diagnosis was 7.5 years.Compared to the Egyptian study by Ghobrial et al. [21], the mean age of FMF cases at the time of the study was younger than ours, 10.4 ± 2.4 years.Still, the other two parameters were nearly similar, with the mean age at the disease onset which was 6.8 ± 3.2 years.The mean age at diagnosis was 7.3 ± 2.5 years.This difference may be related to the different sample sizes between both studies.
Positive family history of FMF was reported in 82.5% of our studied cases, and this is more than the results of Garf et al. [22] and Talaat et al. [4] in which positive family history of FMF was detected in 33.1% and 15.5%, respectively.
As for anthropometric measurements, both groups had statistically significant differences regarding height and waist circumference percentiles.Both were higher in the control group than in the patient group.
Neither group had a statistically significant difference between weight percentiles and BMIZ score.Arslan et al. [23] found similar results in the same age group.Chronic inflammation in FMF patients may explain the decreased anthropometric measurements compared to the control group.Similar to our results, Vampertzi et al. [24] observed no significant differences in systolic and diastolic blood pressure values between FMF patients and the control groups.
SBP systolic blood pressure, DBP diastolic blood pressure, Hb hemoglobin, TLC total leukocytic count, ESR erythrocytes sedimentation rate, HDL high-density lipoprotein, LDL low-density lipoprotein.Normal value in children: hemoglobin 6-18 years, 10-15.5 g/dL; platelet count, 150,000-400,000/mm; TLC > 2 years, 5000-10,000/mm 3 ; ESR, up to 10 mm/h; CRP, < 10 mg/L; AST 16-12 years: 10-50 units/L and 12-18 years: 10-40 units/L; ALT, 4-36 units/L; serum creatinine, 0.3-0.7 mg/ dL; BUN, 5-18 mg/dL; LDL, less than 110 mg/dL; HDL, > 45 mg/dL.Total cholesterol, less than 170 mg/dL; triglycerides 10-19 years, < 90 mg/dL; fasting blood glucose, 70-100 mg/day; insulin, < 17 µU/mL A total of 77.5% of our FMF patients had heterozygous MEFV genotypes, 15% had homozygous genotypes, and 7.5% had compound genotypes.Nearly similar to our study, Talaat et al. [4] found that the heterozygous genotype was the most prevalent genotype among the studied group, affecting 66.3% of the studied group, followed by the homozygous genotype, and then the compound heterozygous genotype with the following frequencies, respectively 25.2% and 8.4%.Regarding gene mutations in other populations, a Turkish study found that 33% of the patients had compound heterozygous, 28.7% had homozygous, and 26.8% had heterozygous mutations [25].The discrepancy of genotypes among different populations is related to other genetic backgrounds and different sample sizes.Among studied cases, the most frequent MEFV gene mutations detected were V726A in 17.5% of the cases, followed by M6941 in 15%.Similar to our results, the most frequent gene mutation in a study done by El-Garf et al. [22] was V726A in 41.2% of the cases, followed by M694V in 32.4% of the studied group.In the Mediterranean basin outside of Egypt, a   HDL levels were higher among the FMF patients group, while LDL levels were lower than those in the control group, and there was a statistically significant difference between FMF patients and the control group as regards HDL and LDL levels; this is contrary to results obtained by other studies which reported lower levels of HDL in adult FMF patients than healthy people [14,28] and another study conducted in children with FMF [29], and this may be due to the age group of our patients and the anti-inflammatory effect of colchicine by improving dyslipidemia as all our patients were on colchicine treatment.Regarding serum insulin and fasting blood glucose, there were no statistically significant differences between both groups.The mean serum insulin level was 13.65 (5.3-29.2) µU/mL in the patients' group and 9.95 (4.8-14.5)µU/mL in the control group.The mean fasting blood glucose in the patients' group was 83.05 ± 9.65 mg/ dL and 82.95 ± 11.19 mg/dL in the control group.Dursun et al. found a mean insulin of 2 (2.0-9.5)µU/mL in the patient's group and 2.7 (2.0-42) µU/mL in the control group.Fasting blood glucose was 86 ± 9 mg/dL in patients and 82 ± 9 mg/dL in the control group [15].
ESR levels were higher in the patients' group than in the control group, and there was a statistically significant difference between both groups.Previous studies also showed similar findings [30].This indicates persistent subclinical inflammation during the attack-free period in FMF patients.The mean of SAA among FMF patients was 82.78 ± 50.68 mg/dL.Similar to our findings, Cakan et al. [31] found increased SAA levels in FMF patients during attack-free periods, suggesting subclinical inflammation even during the attack-free period.
We did not report any case of metabolic syndrome among our FMF patients, which may be due to the small sample size and the short duration of the illness.No pediatric studies regarding metabolic syndrome among children with FMF were found in the literature.Gögebakan et al. [32] showed that MetS was detected among 42.90% of adult patients with FMF included in his study, and it was higher than the metabolic syndrome percentage among the control group.Sarkis et al. [12] showed that MetS prevalence was 17% in adult patients with FMF.Both studies, however, were in the adult age group, and the correlation between metabolic syndrome and FMF in these studies may be due to the long duration of the disease in adults.

Conclusions
We concluded that children with FMF require routine follow-up of metabolic syndrome components, as there was a statistically significant difference between our FMF patients and the control group regarding insulin resistance, which was higher among the FMF patients.More research, including larger sample size, is necessary to determine the frequency of metabolic syndrome in Egyptian children with FMF and the connection between insulin resistance and metabolic syndrome in these children.Prompt control of subclinical inflammation in children with FMF is mandatory to avoid complications of prolonged subclinical inflammation.Also, implementing a diet rich in antioxidants and increased physical activity can improve the quality of life of FMF patients.

Table 1
Demographic, clinical, and laboratory data of patients and control groups

Table 2 FMF disease characteristics Parameters Mean ± SD, median (range), or n (%) Age at onset (years)
FMF Familial Mediterranean fever, MEFV Mediterranean fever, ISSF international severity score for FMF.Serum amyloid A level < 10 mg/dL

Table 3
Relation between insulin resistance among FMF patients and FMF gene mutations