An Immunological Investigation of Hemophilia B with a Tentative Classification of the Disease into Five Variants1

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Abstract
Patients (23) with hemophilia B were investigated by several immunological methods; 16 patients (69.9%) had no detectable factor XI antigen. Five had a normal factor IX antigen and the electrophoretic mobility of this abnormal factor IX was similar to that of its normal counterpart. One of these 5 patients had hemophilia BM, since ox brain thromboplastin clotting time was severely prolonged. The remaining 2 patients had reduced or decreased factor IX antigen. Several patients showed a slight prolongation of ox brain thromboplastin time due to an associated slight factor VII deficiency. On the basis of these results, a tentative classification of hemophilia B into 5 variants is proposed: hemophilia B-, or with no factor IX antigen; hemophilia B+, or with normal factor IX antigen; hemophilia BRA, or with reduced factor IX antigen; hemophilia BM, or with normal factor IX antigen and severely prolonged ox brain thromboplastin; hemophilia B, usually B-, with associated mild factor VII defect. A complete evaluation of the hemophilia B patients is feasible only by means of a battery or tests, i.e., factor IX activity assay, factor IX antigen determination, ox brain thromboplastin clotting time and factor VII activity assay.