MEFV genotype distribution and allele frequencies in familial Mediterranean fever: a 20-year retrospective study of 2,246 individuals from a Palestinian laboratory archive

Technical Summary: MEFV Genotype Distribution and Allele Frequencies in Familial Mediterranean Fever (Palestine)

Problem Statement
Familial Mediterranean Fever (FMF) is the most common monogenic autoinflammatory disease, prevalent among Mediterranean populations including Palestinians. It is caused by variants in the MEFV gene, which encodes the protein pyrin. While the disease is well-characterized globally, robust, population-scale molecular data describing the MEFV mutation landscape specifically within Palestine has been scarce. Existing literature relies on small cohorts, limiting the ability to design rational diagnostic panels, optimize genetic counseling, and plan health services for this high-prevalence population. This study addresses the need for a large-scale, long-term retrospective analysis of MEFV genotypes in Palestine to define the mutation spectrum, allele frequencies, and demographic patterns.

Methodology
The authors conducted a retrospective, laboratory-based analysis of all FMF genetic tests performed at Medicare Diagnostic Laboratories, a network operating across Palestine, between February 2006 and May 2026.

• Cohort: The study analyzed 2,246 evaluable records out of 2,252 total tests (99.7% success rate). The cohort included 1,208 males and 1,038 females, with a mean age of 16.9 years.
• Testing Evolution: Methodologies evolved over the 20-year period. Early testing utilized PCR-restriction analysis targeting five common variants. Later, Sanger sequencing of exons 2, 3, 5, and 10 was introduced. The most recent period employed mutation-specific real-time PCR and reverse-hybridization panels screening up to 24 variants prevalent in the Middle East.
• Data Harmonization: Reports from different platforms were programmatically parsed and consolidated. Genotypes were classified into four categories: negative, heterozygous (single variant), homozygous, and compound heterozygous. "Biallelic" genotypes (homozygous or compound heterozygous) were designated as consistent with a molecular diagnosis of FMF.
• Statistical Analysis: Associations between genotype outcomes and variables (age, sex, collection center) were assessed using Pearson chi-square and Mann–Whitney U tests. Allele frequencies were calculated based on the total number of mutant alleles identified.

Key Results

• Diagnostic Yield: At least one MEFV variant was detected in 1,076 individuals (47.9% of the cohort). Specifically, 26.5% were heterozygous carriers, 14.3% were compound heterozygous, and 7.0% were homozygous. A total of 480 individuals (21.4%) carried a biallelic genotype consistent with FMF.
• Mutation Spectrum: Among 1,566 identified mutant alleles, five variants accounted for 94.6% of the mutational burden:
  1. V726A: 33.5% (524 alleles) – The most frequent variant.
  2. M694V: 20.4% (320 alleles).
  3. E148Q: 16.1% (252 alleles).
  4. M680I: 14.1% (221 alleles).
  5. M694I: 10.5% (164 alleles).
     The remaining 11 variants each contributed less than 1.5% individually.
• Compound Heterozygosity: The most common compound genotype was M680I/V726A (83 individuals), followed by M694V/V726A and M694I/V726A. Compound heterozygosity was roughly twice as common as homozygosity.
• Demographic Trends:
  • Age: Mutation positivity increased significantly with age, rising from 36.0% in children aged 6–10 to 64.6% in adults aged ≥46. Biallelic genotypes showed a similar gradient (10.1% in children vs. ~30–34% in adults). The authors attribute this to referral dynamics rather than biological changes.
  • Sex: No significant difference in mutation positivity was observed between males (49.3%) and females (46.2%).
  • Geography: Testing was distributed across 11 cities. Tulkarem showed the highest positivity rate (55.7%) and the highest proportion of biallelic genotypes (32.3%), though statistical significance varied by city sample size.

Significance and Claims
The paper claims to present one of the largest single-source MEFV datasets reported from Palestine. Its primary contributions and claims include:

1. Distinct Mutation Landscape: The study identifies a mutation spectrum dominated by five variants, with an unusually high contribution from V726A compared to neighboring Arab populations where M694V is often predominant. This suggests a potentially milder average disease burden in this population, given V726A's association with milder phenotypes compared to M694V.
2. Clinical Utility: The finding that five variants capture >94% of disease alleles supports the implementation of a focused, cost-effective primary screening panel (targeting V726A, M694V, E148Q, M680I, and M694I) for the Palestinian population.
3. Genetic Counseling: The high prevalence of biallelic genotypes (21.4%) and the frequency of compound heterozygosity strengthen the case for systematic genetic counseling, cascade testing of relatives, and consideration of carrier screening.
4. Data Limitations: The authors modestly note that as a laboratory dataset, it lacks clinical phenotype correlation (e.g., colchicine response, amyloidosis outcomes). They also clarify that the high positivity rates reflect a referred, symptomatic population and cannot be extrapolated as general population prevalence or carrier frequency estimates.

In conclusion, the study provides a quantitative reference for the molecular epidemiology of FMF in Palestine, validating a targeted screening approach and highlighting the specific dominance of the V726A variant in this region.