Background: Familial Mediterranean Fever (FMF) is the most common monogenic autoinflammatory disorder, characterized by recurrent episodes of systemic inflammation. Although this largely is an autosomal recessive condition, a subset of heterozygous carriers of MEFV mutations exhibit a clinical phenotype consistent with FMF. The mechanisms underlying this phenomenon remain poorly understood.

Objectives: This study aimed to identify differential molecular signatures and potential diagnostic pathways by comparing the transcriptomic profiles of patients with a single pathogenic mutation that display the classical FMF phenotype with those of healthy heterozygous carriers. We also assessed our results with FMF patients with two mutations, and validated key results at the protein level.

Methods: Peripheral blood mononuclear cells (PBMCs) were obtained from 8 FMF patients meeting Eurofever criteria. To avoid confounding effects, all patients were sampled prior to colchicine initiation. Patients included 5 with homozygous MEFV exon 10 mutations, and 3 with a single MEFV exon 10 mutation presenting an FMF phenotype. Additionally, 4 healthy heterozygous MEFV carriers without clinical manifestations served as controls. RNA-sequencing was performed on Illumina Next- Seq550 with Qiaseq library kits. CLC software was used for data analysis. Comparative analyses included: (1) heterozygous FMF patients versus healthy heterozygous carriers, and (2) heterozygous versus homozygous FMF patients. PBMCs and primary human monocytes from healthy donors were isolated and stimulated with type I interferon (IFN) to validate key findings at the proteomic level using immunoblotting and Luminex analysis.

Results: Comparative analysis between heterozygous FMF patients and healthy heterozygous carriers revealed 147 differentially expressed genes meeting the criteria of an FDR p-value ≤ 0.001 and an absolute fold change (fc) ≥ 2. Of these, 96 genes were upregulated, while 51 were downregulated in heterozygous FMF patients. Notably, an IFN signaling signature was prominent in heterozygous FMF patients, characterized by broad upregulation of IFN-related genes, including STAT1 (fc 2.71), STAT2 (fc 2.25), IRF7 (fc 3.47), ISG15 (fc 6.04), IFIT2 (fc 9.58 IFIT3 (fc 19), and USP18 (fc 9.6.). MEFV expression was also increased among heterozygous patients displaying the FMF phenotype. Further comparison of heterozygous and homozygous FMF patients revealed heightened expression of cytokine signaling pathways and a persistent upregulation of IFN-related genes in the heterozygous group. Kinetic analysis of IFN-α-stimulated monocytes and PBMCs of healthy donors confirmed IFN-induced upregulation of Pyrin (encoded by MEFV ), STAT1, ISG15 and several other proteins identified from the transcriptome analysis.

Conclusion: Our findings highlight the role of IFN signaling as a secondary axis driving inflammation in heterozygous FMF patients. The IFN-induced upregulation of MEFV expression and other genes may amplify inflammatory cascades, providing mechanistic insight into the pathogenesis of FMF in this subgroup. These results underscore the importance of IFN signaling in modulating FMF phenotypes and may guide future diagnostic and therapeutic strategies.

REFERENCES: NIL.

Acknowledgements: First two authors contributed equally. This study was supported by Scientific and Technological Research Council of Turkey (TUBITAK) under the Grant Number 120C127 as part of 2247-A National Outstanding Researchers Program, and by research grants from Ghent University (BOF23/GOA/001) and the Fund for Scientific Research (FWO)-Flanders (GOI5722N and G017121N).

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.