A genetic variant of factor IX with decreased capacity for Ca2+ binding.

A genetic variant of factor IX is described that behaves identically to PIVKA/IX (the precursor factor IX molecule induced by the absence of vitamin K or presence of vitamin K antagonists, acarboxy factor IX). It shows an increased electrophoretic mobility in the presence of Ca2+, a low affinity for adsorption to A1(OH)3 and a very low specific coagulant activity. This variant of factor IX has been demonstrated in the plasma of a patient with severe haemophilia B and in the plasmas of a number of possible carriers from the probands' pedigree.