Hemophilia A
Key points
- Hemophilia A is a hereditary blood coagulation (clotting) disorder.
- Hemophilia is a hereditary bleeding disorder of specific blood clotting factors.
- Many blood clotting tests are performed if the person tested is the first one in the family to have a bleeding disorder.
- Standard treatment is infusion of factor VIII concentrates to replace the defective clotting factor.
Definition
Hemophilia A is a hereditary blood coagulation (clotting) disorder. It is caused by a deficient activity of plasma protein factor VIII, which affects the clotting property of blood.
Causes, incidence, and risk factors
Hemophilia is a hereditary bleeding disorder of specific blood clotting factors. There are several types, including hemophilia A and B. Hemophilia A is the most common of these disorders and is the result of a deficiency of clotting factor VIII.
The disorder is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome. Thus, the disorder occurs primarily in males. Females carry two copies of the X chromosome, so if the factor VIII gene on one chromosome is defective, the gene on the other chromosome can compensate. Males, however, carry only one X chromosome, so if the factor VIII gene on that chromosome is defective, they will have the disease.
Females with one defective factor VIII gene are carriers of this trait. Fifty percent of the male offspring of female carriers have the disease and 50% of their female offspring are carriers. All female children of a male hemophiliac are carriers of the trait.
The severity of symptoms can vary with this disease, and the severe forms become apparent early on. Bleeding is the hallmark of the disease and sometimes, though not always, occurs if an infant is circumcised. Additional bleeding manifestations make their appearance when the infant becomes mobile.
Mild cases may go unnoticed until later in life when they occur in response to surgery or trauma. Internal bleeding may happen anywhere, and bleeding into joints is common. Risk factors are a family history of bleeding and being male.
Hemophilia A occurs in about 1 out of 5,000 men.
Symptoms
- Bruising
- Spontaneous bleeding
- Bleeding into joints and associated pain and swelling
- Gastrointestinal tract and urinary tract hemorrhage
- Blood in the urine or stool
- Prolonged bleeding from cuts, tooth extraction, and surgery
Signs and tests
Many blood clotting tests are performed if the person tested is the first one in the family to have a bleeding disorder. Once the defect has been identified, other family members will need less testing to diagnose the disorder.
Tests include:
- Prolonged PTT
- Normal prothrombin time
Written and revised by
Andrey Nailor, M.D.
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