What are the recommended tests for diagnosing Familial Mediterranean fever (FMF)?

Recommended Tests for Diagnosing Familial Mediterranean Fever (FMF)

The definitive genetic diagnosis of Familial Mediterranean Fever requires molecular genetic testing for pathogenic variants in the MEFV gene, with a focus on exons 2,3,5, and 10, which contain the most common disease-causing mutations. 1

Genetic Testing Strategy

• Initial genetic screening should focus on the most common pathogenic MEFV variants, particularly in patients with clinical symptoms suggestive of FMF 1

• A two-step testing strategy is recommended:

  1. First screen for the most common pathogenic variants based on ethnic background 1
  2. If necessary, perform extended search spanning complete coding sequences of relevant genes 1

• For patients of Mediterranean origin, testing should prioritize the four clearly pathogenic MEFV variants (M694V, V726A, M680I, M694I) which are almost exclusively found in these populations 1

• Ethnic background significantly influences mutation prevalence:

  • M694V is the most frequent mutation (40% of alleles) in Israeli children with FMF 2
  • E148Q variant is found at high frequency (20%) in Asian populations 1
  • P.Phe479Leu is especially relevant in Greek and Iranian patients 1
  • P.Pro75Leu (P46L) of TNFRSF1A is common in Arabic and African populations 1

Testing Methods

• Direct mutation analysis by DNA sequencing is the method employed by most laboratories 1

• Other acceptable methods include:

  • PCR with restriction enzyme digest
  • Allele-specific PCR
  • PCR-single-strand conformation polymorphism
  • Primer extension
  • Reverse hybridisation-based kits 1

• Genetic testing should be referred to specialized laboratories with quality management systems to ensure proper test performance and reporting 1

Interpretation of Results

• Finding two clearly pathogenic variants (homozygous or compound heterozygous) confirms the diagnosis of FMF 1
• One clearly pathogenic variant with clinical symptoms may be consistent with FMF, but diagnosis relies primarily on clinical judgment 1
• Failure to identify causal mutations does not exclude the diagnosis, as:
  • The entire gene may not be sequenced in routine settings
  • Standard sequencing could miss certain pathogenic variants (primer variants, inversions, duplications)
  • Mosaicism may be missed by standard sequencing 1

Clinical Considerations

• Genetic testing is particularly valuable for patients who have been suffering from fever of unknown origin for long periods 3
• Patients with severe phenotypes (polyserositis, erysipelas-like erythema, splenomegaly, vasculitis) often show high penetrance of exon 10 mutations, particularly M694V 4
• Consider genetic testing even for patients presenting with rare/uncommon symptoms to prevent misdiagnosis or delayed diagnosis 4
• Clinical criteria remain essential in establishing the diagnosis of FMF, especially when genetic testing is inconclusive 2, 5

Important Caveats

• Finding a single MEFV pathogenic variant in patients of Mediterranean origin does not exclude the possibility of disease-causing mutations in other hereditary recurrent fever genes 1
• The spectrum of FMF-associated signs is broader than previously believed, warranting wider indications for genotyping 5
• Some common polymorphisms (like p.Glu148Gln, p.Arg121Gln) initially reported as pathogenic have been reassigned and may be misleading if reported without proper context 1
• Registry of sequence variants is available online at http://fmf.igh.cnrs.fr/ISSAID/infevers to assist molecular geneticists with interpretation 1