A patient with a hereditary deficiency of Factor IX may develop hemophilia B, a severe bleeding disorder clinically similar to Hemophilia A.


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


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