rs1057517151 — F11 c.291del (p.Tyr98fs)

Factor XI Deficiency — The Coagulation Paradox

Coagulation factor XI (FXI) sits at a pivotal junction in the clotting cascade: it amplifies clot formation in tissues with high fibrinolytic activity — the mouth, nose, and urinary tract — where clots dissolve rapidly and need reinforcement. The F11 gene on chromosome 4q35.2 encodes FXI, and the c.291del frameshift (rs1057517151) removes a single guanine from a GGG triplet run, shifting the reading frame from codon 98 and creating a truncated, non-functional protein. The ClinVar classification is likely pathogenic¹¹ likely pathogenic
ClinVar VCV000371284.3, submitted by Counsyl clinical laboratory, 2016.

This variant exemplifies one of medicine's interesting genetic paradoxes: a loss-of-function mutation that simultaneously raises your bleeding risk and may lower your risk of stroke and venous thromboembolism — because factor XI sits at the intersection of hemostasis (necessary clotting after injury) and thrombosis (pathological clotting that causes heart attacks and strokes).

The Mechanism

FXI is activated by factor XIIa in the contact pathway and by thrombin in a positive-feedback loop. Once activated, FXIa cleaves and activates factor IX, which in turn activates the tenase complex and drives the clotting cascade toward fibrin clot formation²² fibrin clot formation
The c.291del frameshift at codon 98 introduces a premature stop, eliminating the protein's catalytic serine protease domain entirely; no functional FXIa is produced from the affected allele.

The reason FXI deficiency causes a peculiar, site-specific bleeding pattern — rather than global deficiency — is that clot initiation via the extrinsic (tissue factor) pathway proceeds normally. It is clot maintenance that suffers: in tissues rich in fibrinolytic activity (plasminogen activators), FXI-mediated amplification is needed to sustain the clot against dissolution. This is why bleeding in FXI deficiency clusters at fibrinolysis-rich sites³³ clusters at fibrinolysis-rich sites
Antifibrinolytic drugs like tranexamic acid correct this mechanism and are the primary surgical prophylaxis; PMID 27216469 — dental extractions, tonsillectomies, urologic procedures — rather than causing the spontaneous joint bleeds characteristic of hemophilia A and B.

The Evidence

Bleeding risk. A 2022 retrospective study of 198 patients undergoing 252 surgical and obstetric procedures⁴⁴ 198 patients undergoing 252 surgical and obstetric procedures
Handa et al. Thromb Res. 2022; PMID 36521104 found that 13% of procedures resulted in clinically significant bleeding. Personal bleeding history was the strongest predictor (OR 5.92, p=0.001); FXI level itself was a weaker predictor, with a threshold of 40 U/dL showing only 47% sensitivity. A 2016 expert review⁵⁵ 2016 expert review
Wheeler & Gailani. Expert Rev Hematol. 2016; PMID 27216469 quantified the difference between genotype classes: heterozygous carriers face an odds ratio of 2.6 for excessive bleeding; homozygotes face OR 13.0. For high-risk procedures (tooth extraction, tonsillectomy, urologic surgery), approximately 60% of severely deficient patients bleed without prophylaxis⁶⁶ 60% of severely deficient patients bleed without prophylaxis
Wheeler & Gailani 2016 versus far fewer at low-fibrinolysis sites.

A 2025 Italian cohort study of 93 FXI-deficient patients⁷⁷ 93 FXI-deficient patients
Santacroce et al. Int J Mol Sci. 2025; PMID 41009375 found that 88% were heterozygotes with mean FXI levels of 39 IU/dL (range 18–79). Critically, 30.8% of heterozygotes experienced hemorrhagic events — consistent with the known principle that there is no reliable linear correlation between FXI level and bleeding severity (Pearson r = −0.18). A patient at 60 U/dL may bleed after tonsillectomy; another at 25 U/dL may not.

Stroke and VTE protection. The clinical paradox: Salomon et al. Blood 2008⁸⁸ Salomon et al. Blood 2008
115 patients with severe FXI deficiency (activity <15 U/dL) followed in Israel; PMID 18268095 found only 1 ischemic stroke observed vs. 8.56 expected — an approximately 8-fold reduction. A 2022 observational study of 7,578 tested patients⁹⁹ 2022 observational study of 7,578 tested patients
Moser et al. Thromb Haemost. 2022; PMID 34555861 showed FXI deficiency associated with aHR 0.55 for cardiovascular events and aHR 0.45 for VTE (both nonsignificant trends toward protection due to small event numbers, but directionally consistent with the Israeli data). This cardioprotective property of FXI deficiency has driven major pharmaceutical interest in FXI inhibitors as next-generation anticoagulants.

Population context. Severe FXI deficiency affects approximately 1 in 1,000,000 people globally¹⁰¹⁰ 1 in 1,000,000 people globally
MedlinePlus Genetics 2024. In Ashkenazi Jewish populations¹¹¹¹ Ashkenazi Jewish populations
Founder effect — two mutations (Type II and Type III) account for ~96% of affected alleles; PMID 2052060 the disease frequency rises dramatically: 1 in 450 individuals, with a heterozygous carrier frequency of approximately 1 in 8. The c.291del variant (rs1057517151) is a distinct frameshift reported in ClinVar as likely pathogenic — not one of the classic Ashkenazi founder mutations, and population frequency data are not available in gnomAD, consistent with extreme rarity.

Practical Implications

The critical action for carriers of this variant is preoperative disclosure — especially before any procedure involving the mouth, throat, nose, or urinary tract. Antifibrinolytic therapy (tranexamic acid) is the mainstay of surgical prophylaxis for most procedures, targeting the fibrinolytic mechanism underlying site-specific bleeding. For severely deficient patients undergoing major surgery, FXI concentrate or fresh frozen plasma may be required.

Women with FXI deficiency warrant specific attention around childbirth: postpartum hemorrhage risk is elevated, and obstetric teams should be informed in advance. Neuraxial anesthesia appears safe — the Handa 2022 study found no epidural hematomas in 174 neuraxial procedures, including 5 patients with FXI <10 U/dL.

Because FXI deficiency appears protective against ischemic stroke and VTE, carriers should exercise caution before using anticoagulants, antiplatelet agents, or NSAIDs that compound bleeding risk without a clear clinical indication. Conversely, the FXI deficiency status should not prompt thromboprophylaxis — it is not a prothrombotic condition.

Interactions

Compound heterozygosity in F11 — carrying two different loss-of-function mutations on opposite chromosomes — produces a clinical picture equivalent to homozygosity: severe FXI deficiency with <15 U/dL activity. The c.291del variant could compound with any other pathogenic F11 allele (including the Ashkenazi Type II (rs121965063 / E117X) or Type III (rs121965064 / F283L) mutations) to produce severe deficiency in individuals who received one allele from each parent.

Acquired conditions that also impair hemostasis (thrombocytopenia, antiplatelet therapy, liver disease, von Willebrand disease) compound with FXI deficiency to increase bleeding risk beyond what either condition alone predicts. The reverse is also true: individuals with both FXI deficiency and a prothrombotic variant (Factor V Leiden rs6025, or prothrombin G20210A rs1799963) may have partially opposing effects — the FXI deficiency offering some bleeding tendency while the thrombophilic variant pushes toward clotting — producing unpredictable net clinical behavior that warrants specialist assessment.