rs28940579 — MEFV V726A

MEFV V726A — The Moderately Severe FMF Founder Mutation

Familial Mediterranean fever (FMF) is an autoinflammatory disease defined by episodic, self-limiting attacks of fever and serositis — sterile inflammation of the abdominal, pleural, or pericardial lining — lasting 12 to 72 hours, then abruptly resolving. Between attacks, most patients feel well. The gene responsible, MEFV, encodes pyrin¹¹ pyrin
a scaffolding protein that assembles the pyrin inflammasome and controls release of IL-1β, the master cytokine of innate immunity. When pathogenic variants impair pyrin's regulatory capacity, inflammasome activation becomes constitutive, triggering unprovoked inflammatory attacks.

V726A (p.Val726Ala, c.2177T>C) is one of five founder mutations²² founder mutations
mutations that arose in a common ancestral population and were then spread as the population migrated; founder mutations are highly enriched in specific ethnic groups that together account for approximately 74% of FMF chromosomes across Armenians, Arabs, Turks, and Sephardic Jews. It sits in exon 10, the hotspot for severe FMF mutations, alongside M694V and M680I. Unlike E148Q (exon 2, which is debated), V726A is unambiguously pathogenic: ClinVar classifies it Pathogenic/Likely pathogenic across 43 of 56 independent submissions with no conflicts.

The Mechanism

Valine at position 726 sits within the B30.2 (SPRY) domain³³ B30.2 (SPRY) domain
the C-terminal regulatory domain of pyrin that senses RhoA GTPase effector signals and microbial toxins, gating inflammasome activation of pyrin. This domain normally maintains pyrin in an autoinhibited, inactive state through interactions with regulatory kinases PKN1 and PKN2. Substituting valine with the smaller, non-polar alanine at position 726 disrupts a stabilizing contact within the B30.2 fold. The result is decreased PKN1/14-3-3 binding and constitutive activation of the pyrin inflammasome — spontaneous caspase-1 cleavage of pro-IL-1β and pro-IL-18, without the microbial trigger normally required.

The severity of this dysfunction is intermediate. Functional studies show V726A pyrin retains more residual regulatory capacity than M694V — quantified as a higher threshold for spontaneous activation. This mechanistic gradient maps directly onto clinical observations: V726A homozygotes have more manageable disease than M694V homozygotes, and respond better to colchicine prophylaxis.

The Evidence

Genotype-phenotype correlation studies across multiple populations consistently rank V726A as intermediate severity. In a cohort of Arab FMF patients, Majeed et al. (2002)⁴⁴ Majeed et al. (2002) documented a mean severity score of 10±3 for V726A/V726A homozygotes versus 14±2 for M694V/M694V (p=0.003), placing V726A clearly below M694V but above M694I (score 6±1). Crucially, the compound heterozygous M694V/V726A genotype was associated with a severe clinical course, indicating that the severity ranking is genotype-specific rather than intrinsic to V726A alone.

Colchicine response data from Lidar et al. (2012)⁵⁵ Lidar et al. (2012) precisely quantifies the treatment gap between genotypes: V726A homozygotes achieved near-complete attack control (mean 0.08±0.20 attacks/year) on modest colchicine doses (1.13±0.41 mg/day), while M694V homozygotes remained partially active (0.70±1.06 attacks/year) despite requiring 1.98 mg/day, with 40% experiencing dose-limiting side effects. This places V726A homozygotes among the most colchicine-responsive MEFV genotypes.

Amyloidosis risk — the most feared long-term complication of FMF — correlates primarily with M694V genotype and duration of inadequately treated inflammation. V726A carriers have substantially lower amyloidosis rates: the largest pediatric cohort study (Öztürk et al. 2022⁶⁶ Öztürk et al. 2022, n=3,454) recorded only 0.3% secondary amyloidosis prevalence across all genotypes in the colchicine era, and the authors attribute this primarily to tight control in M694V-dominant cases. Heterozygous V726A carriers who are clinically asymptomatic are not at elevated amyloidosis risk.

A 30-year retrospective analysis of genotype-phenotype trends (Yildirim et al. 2025⁷⁷ Yildirim et al. 2025) confirmed that V726A was negatively correlated with severe PRAS (physician rating score) across the study period, reinforcing its classification as a milder exon 10 allele compared to M694V.

Practical Implications

For heterozygous carriers with no symptoms, V726A heterozygosity requires no treatment. FMF is autosomal recessive — a single pathogenic allele is generally insufficient to cause full disease. The carrier state may predispose to subclinical inflammation (elevated SAA or CRP between attacks) in some individuals, but this does not meet the threshold for prophylactic colchicine in asymptomatic adults.

For homozygous V726A carriers or compound heterozygotes with another pathogenic MEFV allele: colchicine is the standard of care, initiated as early as diagnosis. The standard prophylactic dose in adults is 0.5–2 mg/day adjusted to attack frequency. V726A genotype predicts a favorable response — most patients achieve full attack suppression at moderate doses. The primary rationale for strict prophylaxis is preventing AA amyloidosis, which requires sustained subclinical inflammation to accumulate serum amyloid A protein in the kidneys. Uncontrolled FMF — even without obvious fever attacks — elevates SAA levels and drives amyloidosis over years to decades. Colchicine normalizes inter-attack SAA in the majority of V726A-genotype patients.

Monitoring should include periodic urinalysis for proteinuria (screening for early renal amyloidosis) and serum SAA measurement to confirm inter-attack inflammatory suppression.

Interactions

V726A interacts meaningfully with other MEFV variants. Compound heterozygosity with M694V (rs61752717) elevates phenotype severity significantly above V726A homozygosity — Majeed et al. classified M694V/V726A as a "severe" genotype, comparable to M694V/M694V in clinical impact. V726A also participates in the complex allele V726A+E148Q (rs3743930), where both mutations sit on the same chromosome: this cis-combination is more severe than V726A alone, suggesting E148Q modifies pyrin function even in a trans-exon context.

For compound heterozygotes with M680I (rs61752720), disease is typically moderate — less severe than M694V/V726A but more active than V726A homozygosity alone. The specific compound genotype determines colchicine dose requirements and the urgency of prophylaxis.