# Comparative analysis of exon 10 and non-exon 10 variants in children with familial mediterranean fever: a retrospective cohort study

## TL;DR

This study compares the effects of different MEFV gene variants in children with familial Mediterranean fever, finding that exon 10 variants are linked to more severe disease and that non-exon 10 variants can modify disease expression.

## Contribution

The study provides one of the largest pediatric FMF cohorts stratified by MEFV genotype and identifies a modifier role for non-exon 10 variants.

## Key findings

- Homozygous exon 10 variants are associated with earlier disease onset, higher severity, and increased anti-IL-1 therapy use.
- Exon 10–non-exon 10 combinations show a clinically relevant phenotype similar to compound exon 10 carriers.
- Non-exon 10 variants appear to modify disease expression, increasing attack frequency and inflammatory markers.

## Abstract

Familial Mediterranean fever (FMF) is the most common inherited autoinflammatory disorder caused by MEFV variants. Exon 10 variants, particularly M694V, are strongly associated with severe disease, but the impact of non–exon 10 variants in children remains less defined. To evaluate genotype–phenotype correlations in pediatric FMF by comparing patients with homozygous exon 10, compound heterozygous exon 10, and exon 10 combined with non–exon 10 variants. This single-center retrospective cohort study included 477 children fulfilling Eurofever/PRINTO criteria between 2018 and 2025. Patients were stratified into four genotype groups. Clinical features, laboratory parameters, and treatments were compared. Disease severity was assessed with the International Severity Scoring System for FMF (ISSF). Homozygous exon 10 variants were associated with an earlier disease onset, shorter diagnostic delay, higher ISSF scores, and a markedly greater requirement for anti–IL-1 therapy compared with other genotypic categories. Patients with compound exon 10 variants and those with combined exon 10–non–exon 10 variants exhibited broadly comparable overall disease severity, although differences were observed in selected clinical manifestations. In contrast, individuals with combined exon 10–non–exon 10 variants demonstrated higher attack frequency, increased inflammatory marker levels, and higher ISSF scores when compared with patients with a single exon 10 allele, supporting a modifier effect of non–exon 10 variants on disease expression.

Conclusion: Pediatric FMF patients homozygous for exon 10, especially M694V, show a more severe clinical course with higher disease activity and greater biologic treatment requirements. Exon 10–non–exon 10 variants present with attenuated but clinically relevant phenotypes, resembling compound exon 10 carriers. These findings emphasize the prognostic importance of comprehensive MEFV genotyping in risk stratification and individualized management.
What is Known:• Familial Mediterranean fever (FMF) is the most common monogenic autoinflammatory disorder, caused by MEFV gene mutations.• Exon 10 mutations, particularly M694V homozygosity, are associated with more severe disease, higher attack frequency, colchicine resistance, and increased risk of complications such as amyloidosis.What is New:• This is one of the largest pediatric FMF cohorts systematically stratified into homozygous exon 10, compound heterozygous exon 10, exon 10–non–exon 10 groups, and single exon 10 allele• Exon 10–non–exon 10 variant combinations were associated with a clinically relevant inflammatory phenotype resembling compound exon 10 genotypes, suggesting a potential modifier role of non–exon 10 variants.

What is Known:

• Familial Mediterranean fever (FMF) is the most common monogenic autoinflammatory disorder, caused by MEFV gene mutations.

• Exon 10 mutations, particularly M694V homozygosity, are associated with more severe disease, higher attack frequency, colchicine resistance, and increased risk of complications such as amyloidosis.

What is New:

• This is one of the largest pediatric FMF cohorts systematically stratified into homozygous exon 10, compound heterozygous exon 10, exon 10–non–exon 10 groups, and single exon 10 allele

• Exon 10–non–exon 10 variant combinations were associated with a clinically relevant inflammatory phenotype resembling compound exon 10 genotypes, suggesting a potential modifier role of non–exon 10 variants.

The online version contains supplementary material available at 10.1007/s00431-026-06835-4.