Key Takeaways
Hemophilia C is an inherited bleeding disorder caused by a deficiency of Factor XI (FXI). It is also known as Factor XI deficiency or Rosenthal syndrome. Unlike hemophilia A and B, hemophilia C is autosomal, not X-linked, so it affects males and females roughly equally [4,5].
- Epidemiology ▾: It is far rarer overall but strikingly common in one group: it affects up to 8% of people of Ashkenazi Jewish descent, compared to about 1 in 100,000 in the general population [4,7].
- Symptoms ▾:Bleeding severity does not reliably match the FXI level. Some people with very low FXI never bleed spontaneously, while others with only a partial deficiency bleed heavily after surgery [5,6].
- Treatment ▾: Treatment of hemophilia C relies on fresh frozen plasma, antifibrinolytic drugs like tranexamic acid, and, where available, factor XI concentrates, chosen carefully because replacement therapy itself carries a rare risk of triggering a clot [6,9].
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Introduction
Hemophilia C is the least familiar member of the hemophilia family, and for good reason: it behaves differently enough from hemophilia A and B that lumping the three together can be misleading. The condition is caused by a shortage of Factor XI (FXI), a clotting protein that sits further upstream in the clotting cascade than Factor VIII or IX. The result is a bleeding disorder that is often mild, frequently unpredictable, and inherited in a completely different pattern from hemophilia A and B.
Epidemiology
In the general population, hemophilia C is rare, affecting roughly 1 in 100,000 people [7]. But prevalence rises sharply in one specific group: people of Ashkenazi Jewish descent, where the carrier frequency for FXI mutations reaches 8% to 9%, and severe, homozygous deficiency affects an estimated 1 in 190 to 1 in 450 individuals [4,5]. A smaller cluster of cases has also been described among Iraqi Jewish and Basque populations [4,8]. Outside these groups, hemophilia C can appear in any ethnicity, but true severe deficiency is genuinely uncommon.
Historical context: Rosenthal syndrome
Hemophilia C was first described in 1953 by Rosenthal and colleagues, who identified an American Jewish family with a pattern of significant post-dental and post-surgical bleeding [6]. The condition still carries the name Rosenthal syndrome in some medical literature, alongside its older laboratory name, plasma thromboplastin antecedent (PTA) deficiency.
The Molecular Basis
This section explains why a deficiency further up the clotting cascade produces a bleeding pattern so different from hemophilia A and B.
The role of Factor XI
Factor XI is a plasma protein made in the liver that circulates as an inactive zymogen, the "before" form of an enzyme. It sits in the intrinsic pathway of coagulation, one step ahead of Factor IX. When activated to FXIa, typically by thrombin in a feedback loop that amplifies clot formation, Factor XI's job is to activate Factor IX, which then goes on to work with Factor VIII to activate Factor X.
This positioning matters. Because FXI mainly acts to reinforce and amplify a clotting response that is already underway, rather than initiate it, its absence does not shut clotting down the way a shortage of FVIII or FIX does. This is the central reason hemophilia C behaves so differently in the body.
Why bleeding is unpredictable
In hemophilia A and B, the severity of bleeding tracks closely with the factor level: less factor generally means more frequent and more severe bleeding. In hemophilia C, this relationship breaks down. Some people with severely low FXI activity have no spontaneous bleeding at all, while others with only a partial deficiency experience serious hemorrhage after surgery [5,6]. Researchers believe this is linked to how well an individual's overall clotting system can generate thrombin through backup pathways, and to the fibrinolytic activity of the tissue involved, rather than the FXI level alone [6].
Bleeding in hemophilia C also concentrates in tissues with naturally high fibrinolytic activity, meaning tissues that are especially good at breaking down clots once formed, such as the mouth, nose, and genitourinary tract [6]. This explains why dental extractions and tonsillectomy are classic triggers, and why the disorder was first noticed in exactly that context.
The genetics behind it
Hemophilia C comes from mutations in the F11 gene, located on the long arm of chromosome 4 [5,6]. Inheritance is autosomal, meaning the gene is not on the X chromosome, so the condition affects males and females equally, unlike hemophilia A and B [4,5]. It is often described as autosomal recessive, since severe deficiency typically requires two altered gene copies, but the pattern is not perfectly recessive: some single-copy (heterozygous) carriers also have a real bleeding tendency, and rare mutations behave in an autosomal dominant fashion [5,6].
- Homozygous or compound heterozygous individuals (two altered gene copies) typically have severe deficiency, with FXI activity below 15 to 20 IU/dL.
- Heterozygous individuals (one altered copy) typically have partial deficiency, with FXI activity in the 20 to 70 IU/dL range, and some of these individuals still bleed significantly with surgical challenge [5].
- Type II and type III mutations are the two founder mutations responsible for most Ashkenazi Jewish cases, and their frequency has been well mapped in Israeli population studies [4].
Clinical Signs and Symptoms
The clinical picture in hemophilia C looks quite different from hemophilia A and B, and this is one of the most important teaching points for students comparing the three conditions.
How hemophilia C differs from A and B
| Feature | Hemophilia A / B | Hemophilia C |
|---|---|---|
| Inheritance | X-linked recessive; mainly males | Autosomal; males and females equally [4,5] |
| Spontaneous bleeding | Common in severe disease | Rare, even with severe deficiency [6] |
| Joint bleeding (hemarthrosis) | Hallmark feature | Rare [6] |
| Bleeding trigger | Can be spontaneous or trauma-related | Almost always trauma, surgery, or dental work [6] |
| Severity vs. factor level | Closely correlated | Poorly correlated [5,6] |
| Typical bleeding sites | Joints, muscles | Mouth, nose, genitourinary tract [6] |
Typical presentations
Post-surgical and post-dental bleeding. This is the classic presentation. Excessive, sometimes delayed bleeding after tooth extraction, tonsillectomy, or other surgery is often what leads to diagnosis, sometimes not until adulthood [6,7].
Mucosal bleeding. Nosebleeds and heavy or prolonged menstrual bleeding are common complaints, particularly in women, and heavy menstrual bleeding can be an underrecognized presentation of hemophilia C [6,7].
Bleeding after childbirth. Because FXI deficiency affects women as often as men, postpartum hemorrhage is a genuine concern that requires planning during pregnancy.
Unlike hemophilia A and B, spontaneous joint and muscle bleeding is rare in hemophilia C, and many people with the condition, even with quite low FXI levels, go through life without ever having a spontaneous bleed [6].
Diagnosis and Monitoring
Diagnosis follows a similar path to hemophilia A and B: an abnormal screening test prompts a specific factor assay, but the interpretation looks different because of hemophilia C's unusual bleeding pattern.
First-line screening tests
| Test | Result in Hemophilia C | Why |
|---|---|---|
| aPTT | Prolonged | FXI is part of the intrinsic pathway, so its absence slows this test, just as in hemophilia A and B. |
| PT | Normal | The extrinsic and common pathways do not depend on FXI. |
| Platelet count | Normal | Hemophilia C is a clotting-protein disorder, not a platelet disorder. |
Prolonged aPTT in Hemophilia C
aPTT prolongation does not reliably predict who will bleed in hemophilia C, unlike in hemophilia A and B [5,6]. A patient can have a markedly prolonged aPTT and a completely unremarkable bleeding history.
Confirming the diagnosis
The Factor XI activity assay (FXI:C) confirms the diagnosis and grades severity, though as noted above, the number itself is a poor predictor of bleeding risk on its own [5]. A thorough personal and family bleeding history carries unusual weight in hemophilia C, arguably more than in hemophilia A or B, because it is often a better guide to real-world risk than the lab value alone [6].
Because standard FXI levels are poor predictors of bleeding, specialized hematology centers increasingly rely on Global Coagulation Assays (GCAs), such as Thrombin Generation Assays (TGAs) or rotational thromboelastometry (ROTEM). These advanced tests measure the blood's overall ability to form a functional clot in real-time, accounting for alternative clotting pathways. A patient with a very low FXI level but a healthy thrombin generation profile may be cleared for surgery with minimal intervention, sparing them unnecessary and potentially risky blood products [11,12].
Genetic testing
Genetic testing of the F11 gene can confirm the diagnosis and is especially useful for identifying the two well-characterized founder mutations in people of Ashkenazi Jewish descent, supporting family and carrier screening [4].
Differential diagnosis
A prolonged aPTT with a normal PT can also point to hemophilia A or B, so a specific factor panel is needed to identify FXI as the deficient factor. Von Willebrand disease should also be considered, distinguished by von Willebrand factor testing, which is normal in isolated hemophilia C.
Treatment and Management of Hemophilia C
Because bleeding is unpredictable and not tightly linked to the lab value, treatment in hemophilia C is built around the individual's personal and family bleeding history and the specific procedure or situation at hand, rather than a fixed factor target.
The treatment toolbox
Why replacement therapy needs caution
This is one of the most distinctive features of hemophilia C management. Because Factor XI sits in a feedback loop that amplifies thrombin generation, and because early concentrate formulations contained trace amounts of activated FXI, case reports have linked FXI concentrate use to thrombotic events, including disseminated intravascular coagulation [9,10]. Modern concentrates are manufactured with added safeguards, such as antithrombin and heparin, specifically to reduce this risk, but the concern is real enough that concentrate use is generally reserved for situations with a genuine bleeding risk, and combining it with tranexamic acid is typically avoided [9].
This is a meaningful contrast with hemophilia A and B, where replacement therapy does not carry a comparable clotting risk.
Trough targets
Experts commonly suggest a trough FXI activity of roughly 30 to 45 IU/dL is generally sufficient for hemostasis in patients with severe deficiency undergoing surgery, though, consistent with the unpredictable nature of the disorder, individual bleeding history should guide the final decision more than the number alone [9].
Perioperative planning
Because bleeding risk is hard to predict from the lab value, a detailed personal and family bleeding history, taken well before any planned surgery or dental work, is one of the most valuable tools available. For the vast majority of minor to moderate procedures and particularly those involving tissues with high natural fibrinolytic activity like the mouth, tranexamic acid alone is the definitive first-line standard of care. By preventing the premature breakdown of clots, it addresses the specific vulnerability of Hemophilia C without exposing the patient to the clotting risks associated with factor replacement [12]. For higher-risk surgery, a hematologist typically plans a combination of FFP or concentrate with careful monitoring [9].
Gene therapy and emerging approaches
Unlike hemophilia A and B, there is currently no approved gene therapy for hemophilia C. Given how mild and variable the disorder often is, and the small patient population, gene therapy has not been a major research priority to date. Small experimental studies have explored whether other clotting factors, and even the hemophilia A drug emicizumab, might help support clotting in FXI-deficient plasma, but these remain investigational and are not part of standard care [9].
While novel therapies for Hemophilia C are limited, the disorder itself has inspired a major new field of cardiovascular research. Medical researchers observed that people with Hemophilia C naturally possess a lower risk of stroke and deep vein thrombosis, yet rarely suffer from severe spontaneous bleeding. Consequently, pharmaceutical companies are currently developing novel anticoagulants (such as milvexian, asundexian, and abelacimab) that intentionally inhibit Factor XI in the general population. These drugs aim to act as safer blood thinners, proving that the unique, mild nature of Hemophilia C holds the key to preventing pathological clots without causing dangerous bleeding [13].
Long-Term Complications
Hemophilia C's complication profile looks quite different from hemophilia A and B, largely because the joint damage that dominates those conditions is uncommon here.
What is different
Because spontaneous joint and muscle bleeding is rare, hemophilic arthropathy, the hallmark long-term complication of hemophilia A and B, is not a typical feature of hemophilia C [6]. This is a significant quality-of-life difference between the conditions.
What remains a concern
- Surgical and dental risk persists throughout life and requires planning before every procedure, not just a one-time diagnosis.
- Obstetric bleeding risk is a genuine concern for women with hemophilia C and requires coordination with obstetric and hematology teams during pregnancy and delivery.
- Psychological burden can still be significant, particularly the unpredictability itself; not knowing in advance how a given procedure will go is its own source of stress for patients and families.
- Thrombotic risk from treatment, discussed above, is a complication of management rather than of the disease itself, but is worth including here because it shapes how care is delivered over a patient's lifetime.
Frequently Asked Questions
Is hemophilia C the same as hemophilia A or B, just milder?
No. Hemophilia C is a genuinely different disorder. It is caused by a deficiency of Factor XI rather than Factor VIII or IX, it is inherited in an autosomal rather than X-linked pattern, and it affects males and females equally. Bleeding tends to follow surgery or trauma rather than happening spontaneously, and joint bleeding, the hallmark of hemophilia A and B, is uncommon [4,5,6].
Why does hemophilia C affect men and women equally, unlike hemophilia A and B?
The F11 gene is located on chromosome 4, not on the X chromosome. Hemophilia A and B are X-linked, which is why they mainly affect males. Hemophilia C is autosomal, so both sexes can be affected [4,5].
If my Factor XI level is very low, does that mean I will bleed a lot?
Not necessarily. Unlike hemophilia A and B, the FXI level in hemophilia C does not reliably predict bleeding risk. Some people with very low levels never have a spontaneous bleed, while others with only a partial deficiency bleed significantly after surgery. Personal and family bleeding history matters as much as the lab number [5,6].
Why is Ashkenazi Jewish ancestry relevant to hemophilia C?
Two specific F11 founder mutations are unusually common in the Ashkenazi Jewish population, with a carrier frequency of around 8% to 9%. This makes hemophilia C far more common in this group, up to 8% affected in some estimates, than in the general population, where it affects roughly 1 in 100,000 people [4,7].
Is there a cure for hemophilia C?
There is no cure, and unlike hemophilia A and B, no gene therapy is currently approved. Management instead relies on avoiding unnecessary factor exposure, using tranexamic acid where possible, and reserving fresh frozen plasma or factor XI concentrate for situations with a genuine bleeding risk [9].
Why does Factor XI concentrate need to be used carefully?
Factor XI concentrate has, in some cases, been linked to thrombosis, a clot forming where it shouldn't, because trace activated factor XI in early formulations could trigger clotting rather than just replace the missing protein. Modern products include safeguards to reduce this risk, but clinicians still use concentrate selectively rather than routinely [9,10].
Glossary of Related Medical Terms
- Hemophilia C: A bleeding disorder caused by a deficiency of Factor XI. Also called Factor XI deficiency or Rosenthal syndrome.
- Factor XI (FXI): A clotting protein that helps activate Factor IX, amplifying an already-started clotting response.
- Zymogen: An inactive form of an enzyme that must be activated before it can work; Factor XI circulates as a zymogen.
- Autosomal: Located on a chromosome other than the X or Y sex chromosomes; hemophilia C is autosomal, unlike hemophilia A and B.
- Fibrinolysis: The natural process of breaking down a blood clot; tissues with high fibrinolytic activity, like the mouth, are more prone to bleeding in hemophilia C.
- Homozygous: Having two copies of the same altered gene, typically associated with severe FXI deficiency.
- Heterozygous: Having one altered and one normal gene copy; in hemophilia C, some heterozygous carriers still have real bleeding symptoms.
- Founder mutation: A specific genetic mutation traced to a shared ancestor, common in a defined population; two founder mutations account for most Ashkenazi Jewish cases of hemophilia C.
- Fresh frozen plasma (FFP): Donated plasma containing all clotting factors, including Factor XI, used to treat bleeding when concentrate is unavailable.
- Factor XI concentrate: A purified clotting factor product used to raise FXI levels directly, used cautiously due to a rare thrombosis risk.
- Antifibrinolytic: A drug, such as tranexamic acid, that prevents a clot from breaking down too quickly; often effective on its own in hemophilia C.
- Thrombosis: The formation of a harmful blood clot inside a blood vessel; a rare but recognized risk of factor XI concentrate.
- aPTT (activated partial thromboplastin time): A clotting screening test that is prolonged in hemophilia C, as in hemophilia A and B, but which does not predict bleeding risk as reliably here.
Disclaimer: This article is intended for educational and informational purposes only. It is not intended to be a substitute for informed professional medical advice, diagnosis, or treatment. While the information presented here is derived from credible medical sources and is believed to be accurate and up-to-date, it is not guaranteed to be complete or error-free. See additional information.
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