Objective: Familial Mediterranean fever (FMF), an autosomal recessively inherited autoinflammatory disorder, is caused by missense mutations in the pyrin-encoding MEFV gene. The MEFV mutations can be detected in the majority of FMF patients, but there is an important proportion of patients with the FMF phenotype who carry a single or no coding region mutation. This study aimed to investigate the promoter region and 3'-UTR polymorphisms of the MEFV gene in a group of FMF patients with no coding region mutations, to identify variations with a possible role in the regulation of MEFV expression.
Methods: The study group consisted of 289 patients with FMF and 103 ethnically-matched healthy individuals of Turkish origin. All individuals were first genotyped for the five most commonly observed mutations (M694V, M680I, V726A, E148Q and M694I). Then, the coding regions of the MEFV gene in patients carrying none of the 5 mutations were amplified and screened using single-stranded conformation polymorphism and DNA sequencing. After the exclusion of patients with mutations in exons, the promoter and 3'-UTR regions of the MEFV gene were investigated in the remainder. For the haplotype analysis, all study groups were genotyped for two of the 3'-UTR single nucleotide polymorphisms (SNP).
Results: Genotyping for five mutations revealed 186 patients (64.4%) with two mutations, 61 patients (21.1%) with one mutation, and 42 patients (14.5%) with no mutation. The carrier rate for healthy controls was found to be 10%. After screening all 10 exons in the patients with none of the 5 mutations, we identified 36 patients (12.5%) who had no coding region mutations. Analysis of the 3'-UTR region in these patients showed two Alu repeats (AluSx and AluSq), which were located in the 3'-UTR of the reference mRNA sequence. Sequencing of the 3'-UTR of the MEFV gene showed several SNPs that were clustered in 2 haplotypes. When we genotyped all study groups for two of the 3'-UTR SNPs (rs2741918 and rs450021), we observed a significant increase in the frequency of heterozygotes for the 3'-UTR haplotypes in the FMF patients with no coding region polymorphisms compared to the healthy controls (75% versus 48.5%, p=0.006, OR=3.2, 95% CI 1.4-7.4).
Conclusion: This study showed a group of 3'-UTR polymorphisms in the MEFV gene that are clustered in two haplotypes. In addition, a genetic association was observed between 3'-UTR polymorphisms and the FMF patients with no coding region mutations. These findings may suggest a role for 3'-UTR sequences in the regulation of MEFV expression.