Formation of a blood clot in response to tissue injury involves the sequential activation of a group of proteins called the coagulation factors. Tissue injury leads to the release of chemicals that activate the blood clotting system, also known as the coagulation cascade. Coagulation factor deficiencies can lead to serious and potentially life-threatening bleeding problems due to defective blood clot formation.
Fibrinogen is a key coagulation factor. The liver produces fibrinogen, also known as coagulation factor I, which circulates in liquid form in the bloodstream. Activation of the coagulation cascade culminates in the conversion of fibrinogen into the gel-like solid fibrin, which forms the matrix of a blood clot.
The inherited disorders afibrinoginemia and hypofibrinoginemia are associated with absent or markedly decreased blood fibrinogen due to impaired production, reports the National Hemophilia Foundation. Severe liver disease can also lead to insufficient fibrinogen production. People with a low fibrinogen level, also known as a factor I deficiency, typically bruise easily; experience nosebleeds and bleeding in the mouth; and have an increased risk for potentially life-threatening bleeding associated with severe injuries.
Factor VIII, also known as anti-hemophiliac factor A, functions midway through the coagulation cascade. A hereditary deficiency of factor VIII causes hemophilia A, also known as classic hemophilia. Hemophilia A is limited to males due to the pattern of inheritance. An asymptomatic mother passes the defective gene to a son, who exhibits the disease. Daughters who inherit the defective gene do not manifest the disease but can subsequently pass the hemophilia gene to their sons.
People with hemophilia A can have mild, moderate or severe disease, depending on the amount of factor VIII in the bloodstream. The National Heart Lung and Blood Institute reports that most people with hemophilia A have severe disease, with less than 1 percent of normal factor VIII activity.
Symptoms of classic hemophilia vary according to the severity of the disease. People with mild hemophilia A often exhibit bleeding problems only in association with severe injury or surgery. Moderate hemophilia A typically causes prolonged bleeding after injuries and may lead to infrequent, spontaneous bleeding. Frequent, spontaneous bleeding episodes and prolonged bleeding after minor injuries characterize severe classic hemophilia, the National Hemophilia Foundation says.
Factor IX, or anti-hemophiliac factor B, interacts with factor VIII in the coagulation cascade. Hemophilia B, also known as Christmas disease, is an inherited deficiency of factor IX. With the same pattern of inheritance as classic hemophilia, Christmas disease occurs almost exclusively in males. People with Christmas disease exhibit the same bleeding patterns seen with classic hemophilia, the National Heart Lung and Blood Institute says. Approximately 60 percent of people with hemophilia B have severe disease, according to the National Hemophilia Foundation.