Mutations affecting the prothrombinase complex in the family under study.

(Top) Schematic representation of FV molecules characterized by the Leiden mutation (FV R506Q), the R2 haplotype (FV H1299R), and the FV defect (FV Y1702C), respectively. The amino acid substitutions linked to the FV H1299R mutation are indicated by the smaller triangles. (Bottom) Expected combined effects of the FV and PT mutations on the activity of the prothrombinase complex. The arrows indicate the increased cofactor activity for the R506Q and H1299R FV molecules and the increased PT levels for the 20210G/A mutation. The crossed arrow indicates the lack in plasma of the FV molecules bearing the Y1702C substitution.