What is hemophilia?

Hemophilia is a rare, inherited bleeding disorder in which blood cannot clot (form a mass) normally at the site of a wound or injury. The disorder occurs because certain blood clotting factors are missing or do not work properly. Because a clot does not form, extensive bleeding can be caused from a cut or wound. Spontaneous internal bleeding can occur as well, especially in the joints and muscles.

Hemophilia affects males only, but there are rare circumstances when a female can be affected with the disorder.

There are two types of inherited hemophilia:

  • Type A, the most common type, is caused by a deficiency of factor VIII, one of the proteins that helps blood to form clots.
  • Type B hemophilia is caused by a deficiency of factor IX.

Although hemophilia is usually diagnosed at birth, the disorder can also be acquired later in life if the body begins to produce antibodies that attack and destroy clotting factors. However, this acquired type of hemophilia is very rare.

How common is hemophilia?

Hemophilia is an extremely rare disorder. Hemophilia A affects 1 in 5,000 to 10,000 males. Hemophilia B is less common, affecting 1 in 25,000 to 30,000 males. Around 60% to 70% of people with hemophilia A have the severe form of the disorder, about 15% have the moderate form, and the rest have mild hemophilia. Hemophilia can occur in all races and ethnic groups.

What causes hemophilia?

The genes that regulate the production of factors VIII and IX are found on the X chromosome only. Hemophilia is caused by mutations in either the factor VIII or factor IX gene on the X chromosome.

If a woman carries the abnormal gene on one of her chromosomes (females have a pair of X chromosomes), she will not have hemophilia herself, but she will be a carrier of the disorder. That means that she can pass the gene for hemophilia on to her children. There is a 50% chance that any of her sons will inherit the gene and will be born with hemophilia. There is also a 50% chance that any of her daughters will be carriers of the gene, without having hemophilia themselves.

It is very rare for a girl to be born with hemophilia, but it can happen if the father has hemophilia and the mother carries the gene for hemophilia.

In about 20% of all cases of hemophilia, the disorder is caused by a spontaneous gene mutation. In such cases there is no family history of abnormal bleeding.

What are the symptoms of hemophilia?

Prolonged external bleeding after trauma and bruising that occurs easily or for no apparent reason, are two major symptoms of hemophilia. Symptoms vary depending on whether the patient has the mild, moderate, or severe form of the disorder:

  • In severe hemophilia, bleeding episodes occur often and with little or no provocation.
  • In moderate hemophilia, prolonged bleeding tends to occur after a more significant injury.
  • In mild hemophilia, a patient might have unusual bleeding only after a major injury, surgery, or trauma.

People with hemophilia may have any type of internal bleeding, but most often it is in the muscles and joints, such as the elbows, knees, hips, shoulders, and ankles. Often there is no pain at first, but if it continues, the joint may become hot to the touch, swollen, and painful to move.

Repeated bleeding into the joints and muscles eventually causes permanent damage, such as joint deformity and reduced mobility.

Bleeding in the brain is a very serious problem for those with severe hemophilia, and may be life-threatening. Signs of bleeding in the brain may include changes in behavior, excessive sleepiness, persistent headaches and neck pain, double vision, vomiting, and convulsions or seizures.

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