Hemophilia B Leyden

HEMOPHILIA B is a hemorrhagic disease inherited in a sex-linked recessive pattern.1 The clinical severity of hemophilia B, which is dependent on factor IX coagulant activity (IX:C), varies between kindreds but not within kindreds and is constant throughout the life of affected persons. Factor IX antigen levels (IX:Ag) in hemophila B, determined by immunologic assays, also vary between and not within kindreds but do not always correlate with IX:C levels. For example, some patients with IX:C levels below 1 per cent of normal (i.e., those with severe hemophilia B) have normal IX:Ag levels, which indicates that the factor IX molecules . . .