What is the primary deficiency in hemophilia A?
Hemophilia A, the commonest hereditary bleeding
disorder, is due to a genetic deficiency of plasma factor VIII. Although the
inheritance is X-linked recessive, approx-imately 30% of those with the disease
acquire it through a spontaneous mutation and, therefore, will present with no
family history of hemophilia. Regardless of how the disease is acquired, it is
primarily a disease of males.
Its incidence approaches 1 in 5,000 male
births. This “classi-cal hemophilia A” should be considered in any male who
presents with unexplained and uncontrolled bleeding.
The plasma factor VIII concentration correlates
strongly with the degree of bleeding seen. Patients with severe hemophilia have
factor VIII levels 1% or less compared with normal. Those with factor levels
2–5% of normal have moderate hemophilia, while patients with factor levels
6–30% of normal have mild disease. It is important to quantify the plasma
levels of factor VIII prior to surgery to assess the risk of bleeding. Patients
with mild hemophilia will usually bleed excessively only after trauma or during
surgery, whereas severe hemophiliacs can bleed sponta-neously 20–30 times a
year, usually into joints and muscle.