(Can also be known as Hemophilia C, Plasma Thromboplastin Antecedent (PTA) Deficiency, Rosenthal Syndrome)
Factor XI was only first recognized in 1953. The incidence of Factor XI is estimated at 1 in 100,000. It is inherited in an autosomal dominant fashion, which means it affects men and women equally. It can occur with greater frequency in people of Ashkenazi Jewish descent because intermarriage among this group has been more prevalent. In Israel, factor XI deficiency has been estimated to be around 8% among Ashkenazi Jews, making it one of the most common genetic disorders in this group.
Factor XI is another part of the cascade of clotting factors that form the chain leading to a protective clot. Some people with Factor XI deficiency may have milder symptoms that those of hemophilia, but there can be quite a bit of variability with this deficiency. Individuals are not likely to bleed spontaneously, and hemorrhage normally occurs after trauma or surgery. Certain procedures carry an increased risk of bleeding such as, dental extractions, tonsillectomies, surgery in the urinary and genital tracts and nasal surgery. Joint bleeds are uncommon. Patients are more prone to bruising, nosebleeds, or blood in the urine. Woman may experience menorrhagia and prolonged bleeding after childbirth.
Diagnosis is made through bleeding time test, platelet function tests and prothrombin time (PT) and activated partial thromboplastin time (aPTT) tests. A specific Factor XI assay is extremely useful in ruling out combined deficiencies.
In the United States, there are no factor XI concentrates available and fresh-frozen plasma is normally used for treatment. Since Factor XI is not concentrated in fresh frozen plasma, considerable amounts of plasma may be required to maintain the factor level. In the case of mouth bleeds, antifibrinolytic products such as Amicar can be helpful.
Currently there are two factor XI concentrates produced in Europe. One is manufactured through Bioproducts Laboratories (BPL) in the UK. The other product is produced in France through LFB and only for limited patient use.