The term "hemophilia" refers to the following two disorders:
Hemophilia A and B are X-linked recessive diseases. They exhibit
a range of clinical severity that correlates well with assayed
factor levels. Severe disease is defined as <1 percent factor
activity, whereas 1 to 5 percent and >5 percent of normal are
defined as moderate and mild disease, respectively. Males within
a family have the same level of deficiency because they share
the same genetic defect. The combined incidence of hemophilia A
and B is 1 in 5,000 live male births. Approximately 80 percent
have hemophilia A, two-thirds of whom have severe disease.
Bleeding may occur anywhere in patients with hemophilia. The
most common sites are into joints and muscles and from the
gastrointestinal tract. Approximately 80 percent of hemorrhage
occurs in the joints; the ankles are most commonly affected in
children, and the knees, elbows, and ankles in adolescents and
adults. Spontaneous hemarthroses are so characteristic of severe
hemophilia as to be almo