Factor VII Activity and Antigen in Haemophilia B Variants

Summary

Twenty three patients belonging to 18 different pedigrees of Haemophilia B were studied with regard to ox-brain prothrombin time and its correlation to factor VII.

Eleven among them were B-negative (no detectable factor IX antigen), five were B-reduced (factor IX antigen detectable but below the normal values) and seven were B-positive (normal levels of factor IX antigen).

Ox-brain prothrombin time was found prolonged (≥ x̄ + 2.5 SD:99% confidence limits) in nine patients. Factor VII Activity (VII: C) was found reduced in 1/11 B-negative, in 2/5 B-reduced and in 4/7 B-positive patients. Factor VII Antigen (VII: Ag) was found normal in all but one patient.

The ratio VII:C/VII:Ag was abnormal in eight patients independently from the variant of Haemophilia B. The underlying defect which causes the prolongation of Ox-brain prothrombin time due to factor VII: C mild deficiency is heterogeneous. Age, a mild Vitamin K deficiency, the presence of an inhibitor of Factor VII activation and other unknown causes, may be responsible for this pattern.

Keywords

Factor VII antigen - Prothrombin time - Haemophilia B variants - Haemophilia B_M

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