Hemophilia C is a rare genetic disorder caused by a missing or defective blot-clotting protein called factor XI (FXI).
The disease was first recognized in 1953 in patients who experienced severe bleeding after dental extractions. To this day, it is not very well known.
This type of hemophilia, also called factor XI deficiency, generally occurs in one of every 100,000 people. Among Ashkenazi Jews in Israel, however, its incidence is as high as 8% due to intermarriage.
Genetics and inheritance
The disorder may be caused by several genetic mutations in the F11 gene, which provides instructions for making FXI.
Hemophilia C is usually inherited in an autosomal recessive pattern, meaning that a person must have two mutated copies of the gene — one from each biological parent — to develop the condition. However, in some cases, the condition may be inherited in an autosomal dominant manner, in which case a single copy of the faulty gene is sufficient to trigger its onset.
Unlike hemophilia A and B, the risk of being affected by hemophilia C is the same for males and females, since the F11 gene is located on chromosome 4, rather than on the X chromosome.
Symptoms of hemophilia C vary greatly and are not always correlated with FXI levels in the blood. In fact, people with lower FXI levels may bleed less than those with higher levels. As a result, it is difficult to predict the severity and frequency of bleeding episodes simply on the basis of how much FXI is present in the bloodstream.
Prolonged bleeding may occur after major physical trauma, such as an accident or surgery. Tooth extraction, tonsils removal, and ablation of the uterus or prostate are examples of surgeries that entail a high risk of bleeding.
People with the disorder also have a strong tendency for nosebleeds and bruises. Unlike other forms of hemophilia, joint bleeds and spontaneous bleeds are rarely seen in people with hemophilia C, nor is the presence of blood in the urine.
In women, hemophilia C may cause menorrhagia, or prolonged heavy menstrual periods, and increase the risk of prolonged postpartum bleeding, which is excessive bleeding that can occur after giving birth.
Various treatments are available for hemophilia C. These include replacement therapy, in which an infusion of the missing clotting FXI is given to patients.
Sources of FXI include fresh frozen plasma, a blood derivative, or FXI concentrates — products that contain a highly concentrated form of FXI. While FXI concentrates are available in Europe, they are not available in the U.S.
Some people with hemophilia C develop inhibitors or neutralizing antibodies against FXI. These are specific proteins produced by the body’s immune system that can mistakenly attack FXI and therefore lower treatment’s effectiveness.
A therapy called NovoSeven has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of patients with hemophilia A or B with inhibitors. Some studies indicate that this therapy also may be effective in treating hemophilia C.
Antifibrinolytics such as Cyklokapron (tranexamic acid), which slow the breakdown of blood clots, also may be used to treat bleeding from the mouth and ease heavy menstrual periods.
Women also may be treated with hormone therapy — administered in the form of birth-control pills — to prevent excessive menstrual bleeding.
Last updated: Dec. 2, 2021
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