Factor X deficiency is a coagulation (clotting) disorder that occurs when an individual has too little factor X, a clotting protein that plays a key role in the coagulation cascade, which is triggered when a blood vessel is damaged. Factor X is also sometimes referred to as the Stuart-Prower factor after the first patients diagnosed with the disorder, or thrombokinase. Factor X is synthesized in the liver in a process that requires vitamin K.
Factor X deficiency is the rarest of all coagulation disorders. These disorders occur when the blood does not form clots properly. Blood clots are clumps of different types of blood cells and clotting factors that stop bleeding after an injury. The process of blood clotting is called coagulation or hemostasis. Factor X plays a crucial role in the coagulation cascade because it is the first enzyme in the pathway of clot or thrombus formation.
When a blood vessel (vein or artery) becomes injured, it narrows to slow blood flow so that clotting can begin. At the same time, the blood that has leaked outside of the injured blood vessel presses against the vessel to help prevent further blood loss. Blood cells called platelets are activated to move toward the site of injury. Once platelets reach the site of injury, a series of reactions by enzymes called coagulation factors lead to the activation of a protein called thrombin. This protein converts a blood clotting factor, fibrinogen, into long strands that form a net around the platelets and blood cells. This net helps trap more platelets to form a blood clot.
The blood clot, also called a thrombus, is a temporary plug to control bleeding. Once the platelets are clumped together, they become activated and stick together. Sometimes blood clots are visible and appear as bruises under the skin or scabs on the skin. Once the blood vessel is healed, other blood factors are released to destroy the clot, which is then dissolved into the blood.
Factor X deficiency can occur at any age, although the most severe forms are evident in infancy. Because of an inability to properly form clots, patients experience prolonged bleeding in response to injuries such as scrapes and cuts or nosebleeds. Patients may experience excessive bleeding after undergoing surgical or dental procedures and may also be more susceptible to bruising. People with factor X deficiency who sustain an injury may be at risk of bleeding to death.
Treatment of factor X deficiency involves replacement of factor X using either fresh frozen plasma or prothrombin complex concentrate. Both of these treatments contain factor X and other clotting factors.
Factor X deficiency is caused by a mutation in the F10 gene, which provides instructions for making the factor X protein. The gene for factor X is found on chromosome 13. More than 13 different mutations have been found in the factor X gene that cause factor X deficiency, and the disease is caused by different mutations in different people. Factor X deficiency is usually inherited as an autosomal recessive trait, meaning an individual must inherit two defective copies of the causative gene, one copy from each parent, for the disease to appear.
Some people with factor X deficiency do not have a family history of the disorder. In these cases, the disease is acquired, or caused by environmental factors. Acquired factor X deficiency can be caused by having low levels of vitamin K or by using some blood thinning medications, such as warfarin, that cause the body to produce an inactive form of factor X. Diseases associated with factor X deficiency include severe liver disease, amyloidosis (a disease in which proteins are deposited in organs or tissues), and certain cancers, such as leukemia and melanoma.
Factor X deficiency does not occur with greater frequency in any one part of the world. Men and women are affected in equal numbers. This disorder affects approximately one out of 1,000,000 people. There is a greater risk of the disease occurring if close relatives intermarry.
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types of the disease
Severe: Patients with severe factor X deficiency have less than 1% of normal factor X activity. These patients are at risk for spontaneous hemorrhage. Injuries may cause fatal bleeding to occur. Patients with severe forms of the disease commonly have joint bleeding, gastrointestinal bleeding, and internal bleeding (hematomas). Spontaneous head and spinal cord bleeding, and bleeding at the site of the umbilical cord may occur.
Moderate: People with moderate factor X deficiency have 1% to 10% of normal factor X activity. These individuals may have occasional bleeding episodes without obvious causes.
Mild: Individuals with mild factor X deficiency have 10% or more of normal factor X activity. These patients are at little risk for spontaneous bleeding but may bleed excessively following serious injury or surgery. In many cases, mild factor X deficiency is not discovered until an injury, surgery, or tooth extraction results in unusual bleeding. Mild factor X deficiency is often not detected until adulthood.