RELATED STORIES • Slide show: How genetic disorders are passed from parents to children HEART & BLOOD Blood/Lymphatic System • Hemophilia • Amyloidosis • Giant cell arteritis • Vasculitis • Thrombocytopenia (low platelet count) • Behcet's disease • Takayasu's arteritis • Wegener's granulomatosis • Idiopathic thrombocytopenic purpura • Churg-Strauss syndrome

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Hemophilia is a disorder of 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 20 clotting factors that are involved in the clotting process.

There are several types of hemophilia. Which type you have depends 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 health concern is deep internal bleeding and bleeding into joints.

About 18,000 Americans have hemophilia. It's a lifelong disease. But with proper treatment and self-care, most people with hemophilia can have an active, productive lifestyle.

Signs and symptoms of hemophilia 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.

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.

Hemophilia is caused by a deficiency of one of your blood's clotting factors:

• 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 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.

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 you have a baby, 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 may lead to the diagnosis. The first episode of bleeding generally occurs by the time a child is 18 months old. If your baby bruises easily as he or she becomes more mobile, see your doctor.

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

• Deep internal bleeding. Hemophilia may cause deep-muscle bleeding. Swelling of a limb 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.

While there's no cure for hemophilia, most people with the disease can lead fairly normal lives.

Treatment of hemophilia varies depending on the severity of your condition:

• Mild hemophilia A. Treatment may involve slow injection of the hormone desmopressin (DDAVP) by your doctor into one of your veins to stimulate a release of more of your own clotting factor to stop the bleeding. Occasionally, desmopressin is given as a nasal medication.
• Moderate to severe hemophilia A or hemophilia B. Your bleeding may stop only after an infusion of clotting factor derived from donated human blood or from genetically engineered products called recombinant clotting factors. You may need repeated infusions if the internal bleeding is serious. Your doctor may also suggest preventive infusions of clotting factor to avoid bleeding episodes before they begin.
• Hemophilia C. You'll need plasma infusions to stop bleeding episodes.

Regular, preventive infusions of a clotting factor two or three times a week may help prevent bleeding. This approach may be a way to reduce time spent in the hospital and away from home, work, or school, and to limit side effects such as damage to joints. Your doctor can train you to do your own infusions of desmopressin or of the clotting factor at home, work or school.

If internal bleeding has damaged your joints, physical therapy can help them function better. Therapy can preserve their mobility and help prevent frozen or badly deformed joints. However, if you've had repeated bouts of bleeding into your joints that have damaged or destroyed your joints, you may need an artificial joint.

For minor cuts
If you or your child experiences a small cut or scrape, using pressure and a bandage will generally take care of the wound. For small areas of bleeding beneath the skin, use an ice pack.

These steps may help you avoid excessive bleeding and protect your joints:

• Exercise regularly. Activities such as swimming, bicycle riding and walking can build up your muscles while protecting your joints. Don't engage in contact sports, such as football, hockey or wrestling.
• Avoid certain medications. Drugs that can aggravate bleeding include aspirin and nonsteroidal anti-inflammatory drugs (Advil, Motrin, others). Instead, use acetaminophen (Tylenol, others), which is a safe alternative for mild pain relief. Also avoid certain blood-thinning medications, such as heparin and warfarin (Coumadin), which prevent blood from clotting.
• Practice good dental hygiene. This can help you avoid the need to have a tooth pulled, which can precipitate excessive bleeding.

If you have hemophilia, wear a medical alert bracelet to let medical personnel know of your condition and the type of clotting factor that's best for you in case of an emergency.

These other tips can help you and your child cope with hemophilia:

• Let people know. Be sure to inform anyone who will be taking care of your child — a baby sitter, workers at your child-care center, relatives, friends and teachers — about your child's condition. Because it's also OK to let your child engage in noncontact organized sports, be sure to let coaches know, too.
• Comfort your child. Stay calm and reassure your child during injections and infusions. Encourage and praise your child when the treatment is complete.