Clinical and Genetic Spectrum of MEFV Variants in Moroccan Patients with Familial Mediterranean Fever

Technical Summary: Clinical and Genetic Spectrum of MEFV Variants in Moroccan Patients with Familial Mediterranean Fever

Problem Statement
Familial Mediterranean Fever (FMF) is a monogenic autoinflammatory disease characterized by recurrent febrile attacks and serositis, caused by variants in the MEFV gene. While the disease is prevalent in Mediterranean populations, including North Africa, there is a scarcity of genotype-phenotype data specifically from Moroccan cohorts. Existing literature suggests significant geographic variation in MEFV variant distribution and clinical severity. Furthermore, the diagnostic landscape is complicated by the presence of variants with uncertain significance (VUS) or low penetrance, and the limitations of targeted genetic screening panels which may miss rare or population-specific alleles. This study addresses the need to characterize the molecular spectrum of FMF in Morocco and explore correlations between specific genotypes and clinical outcomes to improve diagnostic strategies and patient management.

Methodology
The researchers conducted a retrospective, single-center study at Ibn Rochd University Hospital in Casablanca, Morocco, analyzing 32 clinically diagnosed FMF patients who carried at least one MEFV variant out of an initial cohort of 51 screened individuals.

• Genetic Analysis: Molecular analysis utilized two primary methods depending on the clinical context and available testing at the time of diagnosis:
  1. Targeted PCR (StripAssay®): Used in 12 patients (37.5%) to screen for 12 specific variants in exons 2, 3, 5, and 10.
  2. Sanger Sequencing: Performed in 20 patients (62.5%), either as a primary test or for inconclusive/discordant StripAssay results, allowing for broader detection of variants, including R202Q which is not covered by the StripAssay.
     Variants were classified according to ACMG/AMP guidelines.
• Grouping Strategy: For genotype-phenotype analysis, patients were stratified into two predefined groups based on exon 10 involvement rather than individual variant pathogenicity:
  • Exon10-biallelic (n=10): Patients with two exon 10 variants (homozygous or compound heterozygous).
  • Other-MEFV (n=22): All remaining genotypes, including heterozygous carriers, VUS, and low-penetrance variants.
• Statistical Analysis: Due to the small sample size (n=32), non-parametric tests (Mann–Whitney U, Fisher's exact test, Kruskal–Wallis H) were employed. A Benjamini–Hochberg false discovery rate (FDR) correction was applied to account for multiple comparisons. An exploratory composite inflammatory burden score was also calculated using z-standardized values of peak temperature, CRP, and ESR.

Key Contributions and Results

• Genetic Spectrum:

  • M694V was the most frequent variant (37.5%), followed by R202Q (31.2%).
  • A significant proportion of the cohort (59.4%) carried only low-penetrance variants or VUS.
  • The study identified nine distinct variants, including rare ones like R133P and V620D, highlighting the genetic heterogeneity in the Moroccan population.
  • The frequency of R202Q is noted as a minimum estimate, as it could only be detected in patients undergoing Sanger sequencing.

• Genotype-Phenotype Correlations:

  • Inflammatory Severity: Patients in the Exon10-biallelic group exhibited significantly higher inflammatory activity compared to the Other-MEFV group. This included higher peak temperatures (median 41.0°C vs. 39.0°C; q=0.003), higher peak CRP levels (121.5 vs. 57.5 mg/L; q=0.084), and greater attack frequency (2.0 vs. 1.0 episodes/month; q=0.084).
  • Symptom Profile: Despite differences in inflammatory intensity, the prevalence of individual clinical symptoms (e.g., abdominal pain, fever, arthralgia) was comparable between groups. This suggests that disease severity in biallelic exon 10 patients manifests as increased inflammatory intensity rather than symptom diversity.
  • Diagnostic Delay: The Exon10-biallelic group experienced a significantly longer diagnostic delay (median 11.5 years vs. 5.0 years; p=0.019).
  • Complications: AA amyloidosis was observed more frequently in the Exon10-biallelic group (33.3% vs. 4.5%), though the difference did not reach statistical significance (p=0.079) due to the small number of events.

• Treatment Response:

  • The majority of patients (93.8%) responded favorably to colchicine.
  • Two patients with isolated A744S heterozygosity who developed Crohn-like disease associated with spondyloarthritis responded well to anti-TNF therapy (Infliximab).

Significance and Claims
The paper claims that biallelic involvement of exon 10 variants is associated with more pronounced inflammatory activity and longer diagnostic delays compared to other MEFV genotypes in Moroccan patients. The study highlights that objective inflammatory markers (CRP, ESR, attack frequency) may be more informative for assessing disease severity than the diversity of clinical symptoms alone.

A critical finding is the substantial proportion of patients carrying only VUS or low-penetrance variants, and the fact that nearly 40% of clinically diagnosed FMF patients in the initial screening had no detectable MEFV variant on available tests. The authors argue that these findings underscore the limitations of targeted genetic testing strategies (such as the FMF StripAssay®) in this population.

Consequently, the study supports the adoption of broader sequencing approaches and the strengthening of genetic characterization of FMF across Morocco and North Africa. The goal is to enable earlier diagnosis, better identification of patients at risk for severe complications like AA amyloidosis, and more accurate genotype-phenotype correlations, particularly given the high frequency of variants like R202Q and the presence of rare alleles not covered by standard panels. The authors maintain a modest tone, acknowledging that their findings are exploratory due to the retrospective design, small sample size, and lack of uniform genetic testing, and call for confirmation in larger, multicenter studies.