Factor I (also called fibrinogen) deficiency is an inherited bleeding disorder that is caused by a problem with factor I. Due to the body producing less fibrinogen than it should, or because the fibrinogen is not working properly, the clotting reaction is blocked prematurely and the blood clot does not form.
Factor I deficiency is an umbrella term for several related disorders known as congenital fibrinogen defects. Afibrinogenemia (a complete lack of fibrinogen) and hypofibrinogenemia (low levels of fibrinogen) are quantitative defects, meaning the amount of fibrinogen in the blood is abnormal. Dysfibrinogenemia is a qualitative defect in which fibrinogen does not work the way it should. Hypodysfibrinogenemia is a combined defect that involves both low levels of fibrinogen and impaired function.
Afibrinogenemia is an autosomal recessive disorder, which means that both parents must carry the defective gene in order to pass it on to their child. Like all autosomal recessive disorders, afibrinogenemia is found more frequently in areas of the world where marriage between close relatives is common. Hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia can be either recessive (both parents carry the gene) or dominant (only one parent carries and transmits the gene). All types of factor I deficiency affect both males and females.