Absence of mutations at the activated protein C cleavage sites of factor VIII in 125 patients with venous thrombosis.

Resistance to activated protein C (APC), caused by a mutation at amino acid position Arg506 of the factor V gene, has recently been identified as the most prevalent genetic defect associated with venous thrombosis. Similarly to factor V, mutations at the cleavage sites of factor VIII for APC may occur in patients with venous thrombosis. Here we have analysed 125 consecutive patients with incidental or recurrent venous thromboembolism for the presence of mutations at the cleavage sites for APC at amino acid positions Arg336 and Arg562 of factor VIII. Our findings indicate that mutations at these amino acid positions of factor VIII do not occur in the patient group analysed.