Causes



Hemophilia it is causes by a defect in one of the genes that determine how the body makes blood clotting factor VIII or IX. These genes are located on the X chromosomes. Chromosomes come in pairs. Females have two X chromosomes, while males have one X and one Y chromosome. Only the X chromosome carries the genes related to clotting factors. A male who has the abnormal gene on his X chromosome will have hemophilia. A female must have the abnormal gene on both of her X chromosomes to have hemophilia; this is very rare. A female is a "carrier" of hemophilia if she has the abnormal gene on one of her X chromosomes. Even though she doesn't have the condition, she can pass the gene on to her children.

Coagulation begins when platelets stick to a blood vessel at the site of an injury. A cascade of enzyme reactions occurs to produce a web-like protein network that encircles the platelets and holds them in place (platelet phase) to form a clot (coagulation phase). In this cascade, each clotting factor is transformed, in turn, from an inactive to an active form. Three categories of blood proteins play a role in this process: Everyone has two sex chromosomes, one from each parent. Females inherit an X chromosome from their mother and an X chromosome from their father. Males inherit an X chromosome from their mother and a Y chromosome from their father.
 * The coagulation process**
 * **Procoagulant proteins.** These proteins help form clots.
 * **Anticoagulant proteins.** These proteins prevent formation of clots.
 * **Fibrinolytic proteins.** These proteins help dissolve clots that have formed.
 * Hemophilia inheritance**
 * **The gene that causes hemophilia A or B is located on the X chromosome, so it can't be passed from father to son.** Hemophilia A or B almost always occurs in boys, and is passed from mother to son through one of the mother's genes. Most women who have the defective gene are simply carriers and exhibit no signs or symptoms of hemophilia. It's also possible for hemophilia A or B to occur through spontaneous gene mutation.
 * **The gene that causes hemophilia C can be passed on to children by either parent.** Hemophilia C can occur in both boys and girls.