Hemophilia A

Definition

Hemophilia A is a hereditary bleeding disorder caused by a lack of the blood clotting factor VIII. 

Causes

Hemophilia A results from a deficiency (lack) of clotting factor VIII.

The disorder is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome. That means the disorder occurs primarily in males. Females carry two copies of the X chromosome, so if the factor VIII gene on one chromosome doesn't work, the gene on the other chromosome can do the job. Males, however, carry only one X chromosome, so if the factor VIII gene on that chromosome is broken, they will have hemophilia A.

If a woman has a defective factor VIII gene, she is considered a carrier. The gene can be passed down to her children. Half of the male babies born from women who carry the defective gene have a 50% chance of developing the disease. Half of the female babies born from women who have the defective gene have a 50% chance of being carriers. All female children of men with hemophilia carry the defective gene.

The severity of symptoms can vary. Severe forms become apparent early on. Bleeding is the main symptom of the disease and sometimes, though not always, occurs if an infant is circumcised. Additional bleeding problems are seen when the infant starts crawling and walking.

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.