Definition
Parahemophilia or Factor V deficiency is a rare coagulation disorder. It is an inherited condition that affects the ability of the blood to clot. It also termed as Owren’s disease, proaccelerin deficiency or labile factor deficiency.
Frequency
- No apparent racial predilection for factor V deficiency exists.
- Factor V deficiency affects males and females with equal frequency.
- Factor V deficiency affects all ages. The age at presentation indirectly varies with the severity of disease.
- About 1 person in 1 million people is affected with this disease.
Causes
Parahemophilia is caused by a large number of genetic abnormalities. It follows the inheritance pattern as being autosomal recessive. In thisdisorder, the plasma protein Factor V is low or missing. Thus, when certain coagulation is needed the chain reaction does not take place normally. Inheriting a defective Factor V gene or acquiring an antibody that interferes with normal Factor V function also contributes to the presence of the deficiency.
Inhibitor of Factor V can be acquired in the following conditions:
- After giving birth
- After being treated with a certain type of fibrin glue
- After surgery
- With an autoimmune diseases and certain cancers
Physiology of Blood Clotting
Factor V is an essential component in the blood coagulation cascade. It is synthesized by the liver and in megakaryocytes. This plasma protein circulates in an inactive form. When coagulation is taking place, Factor V is converted to an active factor, Factor Va through a limited proteolysis by the presence of the serine protease a-thrombin. Factor together with the activated factor Xa forms the prothrombinase complex. This complex is the one responsible for the rapid conversion of zymogen prothrombin to the active serine protease a-thrombin. Thrombin cleaves fibrinogen to form fibrin, leading to the ultimate step in coagulation, the formation of a fibrin clot.
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Signs and Symptoms
- Nosebleeds
- Bleeding of the gums
- Easy bruising
- Excessive menstrual bleeding (menorrhagia)
- Umbilical stump bleeding
- Excessive bleeding following injury
- Excessive bleeding following surgery
- Excessive bleeding after giving birth
- Prolonged bleeding time
Diagnosis
- factor V assay (showing decreased activity)
- activated partial thromboplastin time (aPTT) test (prolonged)
- prothrombin time (PT) test (prolonged)
- thrombin clotting time (TCT) test
Treatment
- Fresh frozen plasma infusions (FFP). Depending upon availability, solvent-detergent FFP may contain a more reliable level of Factor V than standard FFP.
- Fresh blood plasma infusions
- In acute cases of severe bleeding, the addition of platelet concentrates may be helpful.
- Patients with factor V deficiency can be given oral contraceptives to decrease menorrhagias, thereby improving anemia and decreasing transfusion needs.
- Tooth extraction in a patient with factor V hereditary deficiency is safely performed with both supplementation of FFP and application of local hemostasis.