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At a glance

Hereditary coagulation disorder caused by defective synthesis of plasma protein factor IX. It is the second-most common form of hemophilia, rarer than hemophilia A. The clinical hallmark of hemophilia B is articular hemorrhage. This bleeding is painful and leads to long-term inflammation and deterioration of the articulation. It is typically present in children and affects the ankles, whereas it more often involves the knees and elbows in adolescents and adults. These complications results in permanent articular deformities, misalignment, loss of mobility, and lead to extremities of unequal lengths.


Christmas Disease; F-IX Deficiency.


Hemophilia B was first recognized as a different kind of hemophilia in 1952. It is also called Christmas disease after Steven Christmas, who was first diagnosed with the disease at 5 years of age in 1952 (and who died of AIDS at age 46 in 1993). Sir Jonathan Hutchinson was responsible for naming clinical disorders after patients and has become familiar for serologic research.


1:40,000 males (15-20% of hemophiliacs). Hemophilia B constitutes about 20% of hemophilia cases, and about 50% of these cases have factor IX levels greater than 1%.

Genetic inheritance

X-linked. Defective coagulation factor IX. Gene map location is Xq27.1-q27.2.


Factor IX is a vitamin K-dependent clotting factor. It is activated by either factor XIa or factor VIIa-tissue factor complex. Once activated, it activates factor X in the presence of calcium, phospholipid, and factor VIIIa. Because deficiency of factor VIII or factor IX decreases factor X activity, hemophilia B is clinically indistinguishable from hemophilia A. Affected patients are classified as mild, moderate, or severe. Mildly afflicted patients have factor IX levels 5 to 40% of normal activity, moderately afflicted patients have levels 1 to 5% of normal activity, and severely afflicted patients have less than 1% of normal activity.


Based on assays of factor IX antigen and factor IX activity. According to the residual factor IX activity, the disorder is classified as severe (<1%), moderate (1-5%), or mild (5-20% of normal value). Prenatal and carrier detection are possible with restriction fragment length polymorphism DNA analysis but are contingent upon parental analysis. Elevation of the partial thromboplastin time with normal prothrombin time and bleeding times are found.

Clinical aspects

Early onset of symptoms: increased tendency to bleeding becomes evident in 90% of affected patients by 1 year of age. The bleeding is usually intra-articular, especially the ankles in children. It is associated with severe pain. Clinical picture very similar to hemophilia A, namely, soft tissue hematomas, including retroperitoneal/pharyngeal hemarthroses (75%), often at the same target joint, pseudotumor of bone, with rare erosion into viscera, hematuria, ...

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