FACTOR X (Stuart-Prower Factor) DEFICIENCY
Factor X (FX), or Stuart-Prower factor, deficiency was first identified in the 1950s in the US and England in two patients: Rufus Stuart and Audrey Prower. The incidence of FX deficiency is estimated at 1 in 500,000 to 1 in a million. It is inherited in an autosomal recessive fashion, meaning both parents must carry the gene to pass it on to their children; it affects men and women equally. The factor X protein plays an important role in activating the enzymes that help to form a clot. It needs vitamin K for synthesis, which is produced by the liver.
Acquired FX deficiency can result from a lack of vitamin K, amyloidosis (abnormal buildup of the protein amyloid in various organs) and severe liver disease.
People with mild FX deficiency experience easy bruising, nose or mouth bleeds, and bleeding after trauma or surgery. Symptoms for patients with severe FX deficiency include excessive umbilical cord bleeding, joint bleeds and bruising. More serious bleeds include spontaneous head bleeds, spinal cord bleeds and gastrointestinal bleeds. Women with FX deficiency may have menorrhagia, heavy menstrual bleeding. Pregnant women may experience first trimester miscarriage or other complications during labor and delivery.
Diagnosis is made through family history, prothrombin time (PT) test, partial thromboplastin time (PTT) or activated partial thromboplastin time (APTT) test. Diagnosis can be confirmed by a FX assay.
There is no FX concentrate currently available in the US, although one is currently in clinical trials. Fresh-frozen plasma (FPP) or plasma-derived prothrombin complex concentrates (PCCs) are normally used as treatment. However, the amount of FX varies between PCCs. PCCs should be used cautiously because at higher volumes they can produce blood clots.
Antifibrinolytic agents, such as aminocaproic acid or tranexamic acid, or topical therapies, such as nosebleed powders or fibrin glue, may relieve bleeding symptoms in patients with mild symptoms.