Gene carrying Factor IX: X-chromosome
Inheritance: X-linked recessive, so most patients are males and there is usually a family history
Clinical features depend on the level of Factor IX present.
Mild deficiencies are associated with mild bleeding following surgery or trauma.
Moderate deficiencies (2 to 10% of normal functional activity) may show:
(1) bleeding after minor trauma
(2) occasionally spontaneous bleeding
Severe deficiencies (< 2% of normal functional activity) are associated with:
(1) spontaneous external or internal bleeding (with hemarthroses, intramuscular hematomas, intramucosal hematomas, internal organs)
(2) severe bleeding after surgery or trauma
Some forms of hemophilia B (Hemophilia B Leyden) may become evident at puberty due to the surge in testosterone.
Laboratory findings:
(1) normal PT
(2) prolonged aPTT
(3) normal thrombin time
(4) decrease in Factor IX antigen and/or activity which is typically marked in a symptomatic patient
(5) normal levels of Factor VIII antigen and activity
