Hemophilia occurs when your body lacks one of several clot-forming proteins called clotting factors. The result is prolonged bleeding.

Hemophilia is a bleeding disorder characterized by a deficiency of selected proteins in your blood-clotting system. Clotting is the process by which your blood changes from a liquid to a solid state in order to stop bleeding.

The clotting process makes use of blood particles called platelets and clot-forming proteins called clotting factors. Your blood has 13 clotting factors, identified by roman numerals, that are involved in the clotting process.

Hemophilia occurs in three types — A, B and C — depending on which clotting factor is deficient. All types can cause prolonged bleeding. If you have hemophilia and you have a cut, you'll bleed for a longer time than if your blood clotted normally. Small cuts usually aren't much of a problem. The greater problem is deep internal bleeding and bleeding into joints.

Hemophilia is a lifelong disease. But with medication, replacement of deficient clotting factors and proper self-care, most people with hemophilia can live an active, productive lifestyle.

Signs and symptoms

Signs and symptoms of hemophilia may include:

• Many large or deep bruises

• Joint pain and swelling caused by internal bleeding

• Bleeding within your muscles

• Blood in your urine or stool

• Prolonged bleeding from cuts or injuries, or after surgery or tooth extraction

At first, because of limited mobility, a baby with hemophilia usually won't have many problems related to hemophilia. But as your baby begins to move around, falling and bumping into things, superficial bruises may occur. This bleeding into soft tissue may become more frequent the more active your child becomes. Most of the time, these bumps and bruises aren't serious and don't require medical treatment.

Emergency signs and symptoms of hemophilia may include:

• Bleeding into your head, neck or digestive tract

• Sudden pain, swelling, and warmth of large joints, such as knees, elbows, hips, and shoulders, and of the muscles of your arms and legs

• Bleeding from an injury, especially if you have a severe form of hemophilia

Causes

Three categories of blood proteins play a role in blood clotting. Procoagulant proteins help form clots. Anticoagulant proteins prevent formation of clots. Fibrinolytic proteins help dissolve clots that have formed.

The clotting process involves blood particles called platelets and procoagulant plasma proteins called clotting factors. The process 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 the clot (coagulation phase). In this cascade, each clotting factor is transformed, in turn, from an inactive to an active form.

The cause of hemophilia is a deficiency of one of several of your blood's clotting factors. There are three types, all inherited disorders:

• Hemophilia A. The most common type, hemophilia A is caused by lack of enough clotting factor VIII.

• Hemophilia B. This second most common type is caused by lack of enough clotting factor IX.

• Hemophilia C. This type is extremely rare. Its cause is a lack of clotting factor XI.

Hemophilia A and B occur almost always in boys. Generally, hemophilia A and B pass from mother to son through one of the mother's genes. 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 gene that causes hemophilia A or B is located on the X chromosome. This is why men can't pass along the gene that causes hemophilia to their sons. 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.

Hemophilia C can occur in both boys and girls. The defective gene that causes hemophilia C can also be passed on to children by mothers and fathers, but it follows an inheritance pattern different from that which occurs with hemophilia A and B.

When to seek medical advice

If you're pregnant or considering a pregnancy and have a family history of hemophilia, talk to your doctor. It's possible to test your child during pregnancy to see whether he or she has inherited hemophilia. If your baby boy hasn't been circumcised and bruises easily as he becomes more mobile, see your doctor.

Screening and diagnosis

Screening and diagnosis of hemophilia may occur in several ways. For people with a family history of hemophilia, it's possible to test the fetus during pregnancy to determine if the child is affected by the disease.

Prolonged bleeding following circumcision may be the first indication that a baby boy has hemophilia. On occasion, in boys who aren't circumcised, easy bruising when the child becomes more mobile between the ages of 9 and 18 months may lead to the diagnosis.

Analysis of a blood sample from either a child or an adult can show a deficiency of a clotting factor. Sometimes, mild hemophilia isn't diagnosed until a person has surgery and excessive bleeding results.