Isolation and characterization of factor IX Chapel Hill: comparison to normal human factor IX.

A classification scheme for patients with hemophilia B has been devised. Assessment of factor IX antigen and factor IX coagulant activity has confirmed the genetic heterogeneity of hemophilia B and has shown that some affected patients have normal amounts of factor IX-like protein. An abnormal factor IX, factor IX Chapel Hill, has been isolated from one of these variants and compared structurally and functionally to the purified normal human factor IX molecule. The major difference between factor IX Chapel Hill and normal human factor IX appears to be defective activation of the abnormal molecule by factor XIa and calcium.