Factor X (FX) occupies a pivotal point in the coagulation system, being activated both by Tissue Factor during initiation of clotting, and by activated FIX and FVIII in the propagation phase of blood coagulation. Because of this key position in the coagulation process, the activated form of FX (FXa) is a popular taget for new anticoagulant drugs.
FX deficiency was first discovered in a patient called 'Stuart' from North Carolina. While this patient was being studied, the same clotting factor deficiency was discovered in a female patient called 'Prower'. Researchers realized that both patients had a deficiency of the same new protein and called it the Stuart-Prower factor. It was later renamed Factor X deficiency.
The incidence of FX deficiency is estimated at 1 in 500,000 births. It is inherited in an autosomal recessive fashion, which means it affects men and women equally. Several genetic variations of FX with varying degrees of severity have been described in the medical literature. People with mild forms of the deficiency, usually do not experience bleeding episodes, but do have bleeding after trauma or surgery. Patients with severe forms of the disease, commonly have joint bleeding, gastrointestinal bleeds, and hematomas. Spontaneous head bleeds, spinal cord bleeds and bleeding at the site of the umbilical cord have also been reported. Women with FX deficiency may have menorrhagia or be susceptible to first trimester miscarriage.
FX is dependent on Vitamin K for its complete synthesis in the liver. Therefore, acquired deficiency occurs in patients with Vitamin K deficiency or antagonism (i.e. on coumadin therapy).
Patients with FX deficiency will have prolongation of both the prothrombin time (PT) and the activated partial thromboplastin time (APTT). The diagnosis is confirmed by a specific FX assay. The assay can be performed using a clotting assay based on the PT, or using a specific chromogenic assay. The Thrombosis Research Center offers both assays; the clotting is assay is used for routine confirmation or diagnosis of FX deficiency, while the chromogenic assay is reserved for control of coumdain therapy in patients with a Lupus Anticoagulant.
