What is Hemophilia type A

Hemophilia A is a rare genetic disorder caused by missing or defective factor VIII (FVIII) clotting protein in the blood. It is usually inherited, but in about one-third of known cases, it’s caused by a spontaneous genetic mutation.

Anyone can be diagnosed with hemophilia A. More than half of all patients eventually develop a severe form of the disease.

Genetics of hemophilia type A

Hemophilia A is inherited in an X-linked recessive pattern, meaning that two hemophilia-carrying X chromosomes must be inherited for the disease to be active in women, but in men, only one X chromosome is needed.

Females inherit two X chromosomes, one from their mother and one from their father (XX). Males inherit an X chromosome from their mother and a Y chromosome from their father (XY). This means that if a son inherits an X chromosome from his mother who carries hemophilia, he will have hemophilia. But because women receive two X chromosomes, they will develop the disease only if both chromosomes carry the defective gene.

More information about the genetics of hemophilia A is available in Genetics Home Reference’s Genetic Consultation Handbook.

The following online resources are also helpful:

Stages and symptoms of hemophilia type A

Hemophilia A has three stages: mild (6-49 percent clotting factor VIII in the blood); moderate (1-5 percent factor VIII); and severe (less than 1 percent factor VIII).

Hemophilia A patients might bleed longer than other people, internally or externally, depending on how much clotting factor VIII is in their blood.

People with this type of hemophilia generally bleed only after serious injury or trauma, and often the disease is diagnosed after a symptomatic event, which may only occur in adulthood. For example, women who often experience heavy menstrual periods can hemorrhage after giving birth.

Moderate hemophilia patients tend to have more frequent bleeding episodes after minor injuries, or even spontaneously. In severe cases, bleeding may occur spontaneously in the joints and muscles.

Testing for hemophilia type A

Hemophilia A should be diagnosed and treated at a specialized hemophilia center. Tests that evaluate clotting time and a patient’s ability to form a clot may be ordered to assess the type and severity.

The Genetic Testing Registry (GTR) provides information about genetic tests for this condition. The registry targets healthcare providers and researchers, so patients and consumers with specific questions should ask their healthcare provider or physician.

Therapies for hemophilia type A

People with hemophilia A require lifelong care, preferably at a specialized treatment center.

The replacement therapy approach — in which the missing clotting factor VIII is replaced to prevent complications — generally works well. Replacement therapy is generally used as “episodic therapy” to treat patients with mild or moderate hemophilia A.

Some people with mild forms of the disease may also be treated with desmopressin (DDAVP), which raises FVIII levels in the blood. Antifibrinolytics, which slow the breakdown of clotting factors in the blood, also are used to treat milder forms of the disorder.

Patients with severe hemophilia A might receive periodic factor VIII infusions to prevent bleeding, in an approach referred to as prophylactic therapy.

Patients can administer these infusions at home themselves if they receive training. This is important for people with severe forms of the disease, because the infusion works best within one hour of a bleeding episode. The goal is to stop the bleeding as soon as possible.

Treatments for hemophilia type A

Here is a list of U.S. Food and Drug Administration-approved products for the treatment of hemophilia A:

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