rs121965063 — F11 Glu117Stop (Type II)

Factor XI Glu117Stop — The Ashkenazi Founder Mutation at the Heart of Hemostasis

Coagulation factor XI (FXI) occupies a paradoxical position in the blood clotting system. It amplifies thrombin generation inside growing clots, stabilizes fibrin networks against premature dissolution, and maintains hemostasis in tissues where the body's own clot-dissolving enzymes work aggressively. Yet people who lack FXI entirely rarely bleed spontaneously — their bleeding emerges primarily after surgery, dental procedures, or trauma, concentrated in the mouth, throat, and urinary tract. And in a remarkable cardiovascular twist, their absent FXI protects them against ischemic stroke and deep-vein thrombosis at rates that have made FXI one of the most actively pursued anticoagulation drug targets in the world.

The Glu117Stop mutation is the most prevalent cause of this condition in the Ashkenazi Jewish population. Originally named for the glutamic acid at position 117 of the mature FXI protein (current HGVS nomenclature calls it p.Glu135Ter, counting from the signal peptide initiator), it was identified by Asakai et al. in 1991¹¹ Asakai et al. in 1991
Asakai R, Chung DW, Davie EW, Seligsohn U. Factor XI deficiency in Ashkenazi Jews in Israel. N Engl J Med, 1991 as one of two ancient founder mutations that together account for approximately 96% of defective F11 alleles in this population. The heterozygote carrier frequency among Ashkenazi Jews is approximately 1 in 8 — making this one of the most common inherited bleeding disorders in any single ancestral group.

The Mechanism

The c.403G>T substitution converts the codon for glutamic acid at position 135 (mature protein position 117) into a stop codon (TAA). The resulting transcript is predicted to undergo nonsense-mediated mRNA decay²² nonsense-mediated mRNA decay
NMD is a cellular surveillance mechanism that degrades mRNAs carrying premature stop codons before significant abnormal protein can accumulate; most nonsense variants early in a transcript trigger NMD rather than producing a truncated peptide, leaving no functional FXI protein from the affected allele.

In heterozygous carriers, the intact F11 allele compensates partially, producing roughly 50% of normal FXI activity — typically 20–70 U/dL versus the normal range of 60–150 U/dL. Homozygous carriers produce essentially no FXI, with activity below 15 U/dL — the diagnostic threshold for severe FXI deficiency (hemophilia C or Rosenthal syndrome).

FXI's role in coagulation is primarily in the thrombin feedback loop³³ thrombin feedback loop
Once initial clot formation begins, thrombin circles back to activate more FXI, creating a self-amplifying cycle that deepens fibrin cross-linking and also activates TAFI — an inhibitor of clot dissolution — shielding the clot from fibrinolysis. Because FXI is not essential for the immediate hemostatic response at the moment of vessel injury (the extrinsic pathway covers initial thrombin generation), its absence goes unnoticed under ordinary circumstances. The deficiency is exposed when bleeding occurs in tissues with vigorous local fibrinolytic activity — dental sockets, tonsillar beds, the urogenital tract — where the fibrin-dissolving machinery is simply too powerful for a FXI-deficient clot to resist.

The Evidence

The cardiovascular paradox of FXI deficiency is among the best-documented genotype-protection relationships in hematology. In a study of 115 patients aged 45 or older with severe FXI deficiency⁴⁴ 115 patients aged 45 or older with severe FXI deficiency
Salomon et al., Blood 2008; compared against expected stroke incidence derived from a national stroke survey, only one ischemic stroke was observed against an expected 8.56 (P=.003) — an approximately eight-fold reduction. Notably, no protective effect was seen for myocardial infarction, consistent with FXI's stronger contribution to fibrin-rich venous and cerebral thrombi than to the platelet-rich arterial plaques that cause heart attacks.

Deep-vein thrombosis protection is equally striking. A companion study of 219 severe FXI-deficient patients⁵⁵ 219 severe FXI-deficient patients
Salomon et al., Thrombosis and Haemostasis 2011; zero DVT events compared to 4.68 expected found zero DVT events versus 4.68 expected from population data — a result consistent across three additional control datasets from population-based studies.

Bleeding risk is real but unpredictable. In the largest perioperative series to date, 198 FXI-deficient patients underwent 252 surgical and obstetric procedures⁶⁶ 198 FXI-deficient patients underwent 252 surgical and obstetric procedures
Handa et al., Blood Advances 2023; Mount Sinai Health System 2011–2021; 13% of procedures had bleeding events. Personal history of bleeding was the strongest predictor (OR 5.92, P=.001) — not FXI activity level. An FXI level above 40 U/dL had reasonable specificity (75%) for predicting lower bleeding risk but poor sensitivity (47%), confirming that genotype and activity level alone cannot determine individual bleeding risk.

Phenotypic severity differs between the two Ashkenazi founder variants. Type II homozygotes (Glu117Stop)⁷⁷ Type II homozygotes (Glu117Stop)
Asakai et al. 1991 — mean FXI activity 1.2% vs 9.7% for Type III; Type II homozygotes had more bleeding episodes have lower residual FXI activity and more bleeding episodes than Type III (Phe283Leu) homozygotes. Compound heterozygotes (one Type II + one Type III allele) show intermediate activity of approximately 3.3%.

Practical Actions

The critical clinical window for FXI deficiency management is before a planned procedure, not after bleeding starts. First-line prophylaxis for dental procedures and minor oral surgery is tranexamic acid mouthwash (4.8% solution, 4×/day for 5–7 days post-procedure), which blocks fibrinolysis locally without requiring systemic coagulation factor replacement. For major surgery, fresh frozen plasma (FFP) raises FXI levels; FXI concentrate (available in some countries, including the UK and Israel) offers more controlled dosing. A critical ceiling: FXI replacement above 70 U/dL carries paradoxical thrombotic risk — the same protein's absent version is cardioprotective, and over-correcting the deficiency can flip the balance.

The Ashkenazi Jewish population context is important for family planning: with a heterozygote frequency of ~1 in 8, partner carrier testing is strongly recommended for Ashkenazi Jewish individuals who carry this variant. If both partners carry a defective F11 allele, the offspring risk of severe homozygous deficiency is 1 in 4.

Interactions

The Type II (Glu117Stop) mutation is compound-heterozygous with the Type III (Phe283Leu; rs121965064) mutation in a substantial fraction of Ashkenazi Jewish patients with severe FXI deficiency. Compound heterozygotes show intermediate FXI activity (~3.3%) and intermediate bleeding phenotype between Type II and Type III homozygotes. When this variant is found in conjunction with a second F11 null allele (from rs1057516616 frameshift or rs1057517151 frameshift, for example), the resulting severe deficiency carries the same management requirements as homozygous Glu117Stop.

The FXI cardiovascular protection intersects meaningfully with prothrombotic variants. A carrier of this variant who also carries Factor V Leiden (rs6025) or the prothrombin G20210A mutation (rs1799963) faces an uncertain net coagulation balance — the FXI deficiency may partially offset the thrombophilic risk, but this interaction has not been studied rigorously and specialist hematology assessment is needed rather than assuming either variant dominates.