Hemophilia is a rare inherited disorder in which the blood does not clot normally. About 18,000 people in the U.S. have hemophilia. Each year, about 400 babies are born with the disorder. Hemophilia usually occurs in males (with very rare exceptions).

People who have hemophilia may bleed for a long time after an injury or accident. They also may bleed into their knees, ankles and elbows. Bleeding in the joints causes pain and, if not treated, can lead to arthritis. Bleeding in the brain, a very serious complication of hemophilia, requires emergency treatment.

The main treatment is injecting the missing clotting factor into the bloodstream.

Signs and symptoms

Signs and symptoms of hemophilia vary depending on the severity of your deficiency of clot-forming proteins called clotting factors. If levels of your deficient clotting factor are very low, you may experience spontaneous bleeding. If levels of your deficient clotting factor are mild to moderately low, you may bleed only after surgery or trauma.

Symptoms of spontaneous bleeding may include:

• Many large or deep bruises
• Joint pain and swelling caused by internal bleeding
• Unexplained bleeding or bruising
• Blood in your urine or stool
• Prolonged bleeding from cuts or injuries, or after surgery or tooth extraction
• Nosebleeds with no obvious cause
• Tightness in your joints

Emergency signs and symptoms of hemophilia may include:

• 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
• Painful, lasting headache
• Repeated vomiting
• Extreme fatigue
• Neck pain
• Double vision

Babies with hemophilia
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.

Causes

Three categories of blood proteins play a role in blood clotting:

• 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.

The coagulation 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 a clot (coagulation phase). In this cascade, each clotting factor is transformed, in turn, from an inactive to an active form.

Your blood has 20 clotting factors that are involved in the clotting process. The cause of hemophilia is a deficiency of one of your blood's clotting factors. Which type of hemophilia you have depends on which clotting factor is deficient:

• 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 rare in the United States. Its cause is a lack of clotting factor XI, and symptoms are generally mild with this type of hemophilia.

Hemophilia A and B
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
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. He or she may refer you to a medical genetics specialist or a specialist in bleeding disorders, who can help you determine if you are a carrier of hemophilia. If you are a carrier, it's possible to test your child during pregnancy to see whether he or she has inherited the condition.

If you have a baby boy, prolonged bleeding following circumcision may be the first indication that he has hemophilia. On occasion, in girls and in boys who aren't circumcised, easy bruising when the child becomes more mobile may lead to the diagnosis. The first episode of bleeding generally occurs by the time a child is 2 years old. If your baby bruises easily as he or she becomes more mobile, see your doctor.

Screening and diagnosis

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.

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 after a person has undergone surgery and excessive bleeding results.

Complications

Complications may occur from the disease or from the treatment for the disease:

• Deep internal bleeding. Hemophilia may cause deep-muscle bleeding that leads to swelling of a limb. The swelling may press on nerves and lead to numbness or pain. This may result in a reluctance to use the limb.
• Damage to joints. Internal bleeding may also put pressure on and damage joints. Pain sometimes may be severe, and you may be reluctant to use a limb or move a joint. If bleeding occurs frequently and you don't receive adequate treatment, the irritation may lead to destruction of the joint or to the development of arthritis.
• Infection. People with hemophilia are more likely to receive blood transfusions and are at greater risk of receiving contaminated blood products. Until the mid-1980s, it was more common for people with hemophilia to become infected with the human immunodeficiency virus (HIV) or with hepatitis through contaminated blood products. Since then, blood products are much safer because of steps taken to screen the supply of donated blood. The risk of infection through blood products has decreased substantially since the introduction of genetically engineered clotting products called recombinant factors, which are free of infection. However, it's still possible for people who rely on blood products to contract other diseases. If you have hemophilia, consider receiving immunization against hepatitis A and B.
• Adverse reaction to clotting-factor treatment. Some people with hemophilia develop proteins in their blood that inactivate clotting factors used to treat bleeding.