rs28940578 — MEFV M694I

MEFV M694I — A Founder FMF Mutation with Moderate Severity and High Colchicine Response

Familial Mediterranean fever¹¹ Familial Mediterranean fever
FMF; an autoinflammatory disease caused by dysregulation of the pyrin inflammasome, characterized by recurrent self-limiting attacks of fever, peritonitis, pleuritis, and arthritis is the most common hereditary periodic fever in the world. The MEFV gene encodes pyrin, a protein expressed in myeloid cells that normally suppresses inflammasome activation in the absence of microbial toxins. Of the hundreds of documented MEFV variants, five founder mutations — M694V, V726A, M680I, M694I, and E148Q — account for roughly 74% of FMF chromosomes in classic cases. M694I (p.Met694Ile) sits at codon 694 in exon 10, just two nucleotides from the more severe M694V mutation, yet the isoleucine substitution confers a distinctly milder phenotype. While M694V dominates the European and Turkish mutation landscape, M694I is the signature exon 10 mutation in East Asian FMF patients and a founder allele in Lebanese kindreds.

The Mechanism

Exon 10 of MEFV encodes part of pyrin's B30.2/SPRY domain, the region that senses microbial toxins and interacts with the regulatory kinases PKN1/2 that keep the inflammasome dormant. Pathogenic exon 10 missense variants impair this gate, allowing unrestrained caspase-1²² caspase-1
the protease that cleaves pro-IL-1β and pro-IL-18 into their active inflammatory forms activation and cytokine release. M694I replaces methionine with isoleucine — a relatively conservative change compared to M694V's valine substitution — but still destabilizes the B30.2 regulatory interface sufficiently to dysregulate pyrin gating.

A 2025 CRISPR/Cas9 knock-in mouse study (Koga et al.³³ Koga et al.) showed that M694I knock-in homozygous mice develop a selective enhancement of Th17 cell differentiation alongside elevated serum G-CSF, IFN-γ, IL-1α, IL-5, IL-6, and TNF-α (all P < 0.05), with significantly reduced survival (P < 0.001). This identifies a Th17-driven inflammatory axis as a specific downstream effect of M694I — distinct from the predominantly IL-1β/monocyte-driven mechanism of M694V — and points toward potential IL-17-pathway therapeutic targets for refractory cases.

The Evidence

The clinical picture of M694I emerges most clearly from Arab and East Asian cohort studies, where it appears at clinically significant frequencies. Majeed et al. (2002)⁴⁴ Majeed et al. (2002) genotyped 278 Arab FMF patients and found that the M694I/M694I genotype carried a mean severity score of 6 ± 1 — compared to 14 ± 2 for M694V/M694V and 10 ± 3 for V726A/V726A (P = 0.003). In this Arab cohort, M694I/M694I represented 14% of identifiable biallelic genotypes. The severity differential is strikingly wide: M694I homozygotes experienced disease roughly half as severe as exon-10-mutation compound heterozygotes.

In Japan, where M694V is essentially absent, M694I is the primary exon 10 mutation. Tsuchiya-Suzuki et al. (2009)⁵⁵ Tsuchiya-Suzuki et al. (2009) found M694I in 42.5% of 80 Japanese FMF patients, predominantly as E148Q/M694I compound heterozygotes (25%) or heterozygous M694I carriers (17.5%). The national registry study by Migita et al. (2012)⁶⁶ Migita et al. (2012) confirmed E148Q/M694I (19.8%) and M694I alone (12.7%) as the dominant mutation patterns in 126 Japanese patients, with colchicine effective in 91.8% at a low mean dose of 0.89 mg/day. In a 116-patient Japanese cohort, Kishida et al. (2014)⁷⁷ Kishida et al. (2014) found M694I carriers had a more severe clinical course than E148Q carriers but a very favorable colchicine response, suggesting the mutation is clinically meaningful but pharmacologically manageable.

Risk of AA amyloidosis exists but is lower than for M694V. Nakamura et al. (2014)⁸⁸ Nakamura et al. (2014) reported a 51-year-old Japanese male with M694I/M694I who developed biopsy-confirmed renal AA amyloidosis; colchicine resolved both the inflammatory attacks and kidney dysfunction. This case establishes that M694I homozygosity can — given sufficient inflammatory burden and decades without suppressive therapy — progress to the same amyloid complication that defines the natural history of severe FMF.

Practical Actions

For heterozygous carriers, clinical FMF from a single M694I allele is rare; disease typically requires biallelic mutations or compound heterozygosity with a second pathogenic MEFV allele. However, heterozygous carriers should receive genetic counseling because their offspring have a 50% chance of inheriting the allele, and if both partners carry MEFV mutations, the risk of homozygous or compound heterozygous children is significant.

For homozygous or compound heterozygous carriers: colchicine at 0.5–1 mg/day is the standard and highly effective first-line treatment. Japanese registry data show greater than 90% colchicine response rates in M694I-positive patients at lower doses than required for M694V. Monitoring serum amyloid A (SAA) and CRP between attacks provides the earliest signal of sustained subclinical inflammation, the primary driver of long-term amyloidosis risk. Annual urine protein screening is recommended by EULAR FMF guidelines for any biallelic MEFV carrier to detect early renal AA amyloidosis before kidney function declines.

Interactions

The most clinically important interaction for M694I is compound heterozygosity with the exon 2 variant E148Q (rs3743930). This combination — E148Q/M694I — is the dominant mutation pattern among Japanese FMF patients. In a pediatric cohort study (Miyashita et al. 2022⁹⁹ Miyashita et al. 2022), compound E148Q/M694I children had typical FMF attacks with dramatically elevated IL-18 (2,806 ± 2,107 pg/mL during afebrile phases), while single-mutation carriers of either E148Q or M694I alone showed no fever or serositis — pointing to a true synergistic inflammasome interaction. Lebanese founder-effect families carrying M694I as part of a complex haplotype (Medlej-Hashim et al. 2011, PMID 20937419) show that M694I behaves as a fully penetrant disease allele when combined with another pathogenic MEFV mutation. M694I can also compound with M694V (rs61752717), M680I, and V726A (rs28940579), though these combinations are less commonly reported than E148Q/M694I.