rs3743930 — MEFV E148Q

MEFV E148Q — The Most Debated Variant in Autoinflammatory Disease

The MEFV gene encodes pyrin¹¹ pyrin
a scaffolding protein that assembles into the pyrin inflammasome and regulates IL-1β and IL-18 release, the two cytokines that drive the spiking fevers and serositis of familial Mediterranean fever (FMF). Most pathogenic MEFV mutations cluster in exon 10 — M694V, M680I, V726A — and produce a structurally destabilized pyrin that cannot properly gate inflammasome activation. E148Q is different: it sits in exon 2, changes a glutamic acid to the chemically similar glutamine (a conservative substitution), and is carried by as many as 25–28% of East and South Asian individuals — a population frequency that makes classic Mendelian disease causation implausible.

The Mechanism

Pyrin's B30.2 domain, encoded by exon 10, is the primary site that senses microbial toxins and interacts with the regulatory kinases RhoA-DIRAS3 and PKN1/2. The exon 10 FMF mutations bypass this gating mechanism, leading to unrestrained caspase-1 cleavage of IL-1β precursor. E148Q affects exon 2 instead, where pyrin's PYRIN domain²² PYRIN domain
the N-terminal signaling module that recruits ASC and initiates downstream caspase activation resides. The substitution p.Glu148Gln is predicted to be tolerated by all computational missense-effect algorithms (SIFT, PolyPhen-2), consistent with the conservative nature of the glutamate-to-glutamine change. In vitro functional studies have yielded mixed results: one assay showed decreased suppression of IL-8 secretion, while a colchicine-response assay found no difference from controls. The net effect on pyrin function appears small compared to exon 10 mutations, which explains both the high population frequency and the debate over pathogenicity.

The Evidence

The debate has been running for over two decades. On the benign side: Tchernitchko et al. (2003)³³ Tchernitchko et al. (2003) genotyped 233 FMF patients and 213 disease-free Sephardic Jewish relatives and found identical E148Q allele frequencies (3.62% vs 3.75%, p=0.93), leading them to conclude it "is not implicated in the development of FMF." The gnomAD v4 exome dataset contains 2,140 homozygous individuals — a scale inconsistent with a fully penetrant autosomal recessive disorder.

On the pathogenic side: Topaloglu et al. (2005)⁴⁴ Topaloglu et al. (2005) examined 26 homozygous E148Q patients and found 77% had recurrent abdominal pain, 66% episodic fever, and 50% arthralgia — features indistinguishable from classic FMF. Most required colchicine therapy. A follow-up study (Topaloglu et al. 2018⁵⁵ Topaloglu et al. 2018) confirmed that E148Q homozygotes have milder disease than exon 10 carriers (50% mild, 46.7% moderate, 3.3% severe) with a high colchicine response rate (73.3% complete response). A 2024 pediatric cohort in Druze patients — where E148Q reaches 56% prevalence — (Awaad et al.⁶⁶ Awaad et al.) found objective colchicine responsiveness (falling CRP levels) in all treated carriers, providing functional support for pathogenic relevance in that population.

The current consensus leans toward E148Q being a low-penetrance modifier rather than a classical disease allele: symptomatic expression depends on genetic background, compound heterozygosity with other MEFV alleles, and ethnicity. ClinVar (VCV000002542) reflects this tension: 31 active submissions include 1 pathogenic, 16 uncertain significance, 8 likely benign, and 6 benign. Major clinical labs (Labcorp, Invitae, Mayo Clinic) classify it as likely benign or benign.

An intriguing counterpoint: Lidar et al. (2013)⁷⁷ Lidar et al. (2013) found E148Q significantly overrepresented among Ashkenazi Jewish nonagenarians (19.8% vs 2.6% in the general Ashkenazi population, p<0.0001), raising the hypothesis that chronic low-grade inflammasome priming from E148Q may enhance resistance to infections — an evolutionary trade-off analogous to sickle cell and malaria resistance.

Practical Actions

For heterozygous carriers, no treatment is needed unless there are recurring unexplained fever episodes or inflammatory attacks meeting clinical FMF criteria. For homozygous individuals, the picture is more actionable: colchicine (0.5–1 mg/day) is the standard prophylactic therapy for symptomatic FMF regardless of genotype, and most E148Q/E148Q patients with symptoms respond completely. Monitoring serum amyloid A (SAA) and CRP between attacks is recommended in FMF guidelines because sustained subclinical inflammation is the key driver of amyloidosis — the most serious long-term complication of FMF, and the one complication where E148Q has occasionally been documented in the literature.

For asymptomatic homozygotes (at least 4 of 26 in one study had no symptoms), periodic urinalysis for proteinuria (every 4–6 months) is recommended to screen for early AA amyloidosis, as per European League Against Rheumatism (EULAR) FMF guidelines.

Interactions

E148Q shows its most clinically significant behavior as a compound heterozygote with exon 10 mutations. The complex allele V726A+E148Q (both mutations on the same chromosome) produces disease more severe than V726A alone, suggesting E148Q does modify pyrin function even if it cannot cause FMF in isolation. Compound heterozygotes carrying E148Q with M694V (related SNP rs61752717) or M680I (rs61752720) are significantly less severely affected than M694V homozygotes, but still clinically symptomatic and typically require colchicine. For any E148Q carrier with FMF-like symptoms, complete MEFV panel testing including all common exon 10 variants is essential before concluding the genotype explains the phenotype.