Low prevalence of the factor V Leiden mutation among "severe" hemophiliacs with a "milder" bleeding diathesis.

Patients with hemophilia A and B and factor levels than 1 percent of normal bleed frequently with an average number of spontaneous bleeding episodes of 20-30 or more. However there are patients with equally low levels of factor VIII or factor IX who bleed once or twice per year or not at all. To examine whether the presence of a hereditary defect predisposing to hypercoagulability might play a role in ameliorating the hemorrhagic tendency in these so-called "mild severe" hemophiliacs, we determined the prevalence of prothrombotic defects in 17 patients with hemophilia A and four patients with hemophilia B selected from 295 and 76 individuals with these disorders, respectively, followed at a large Italian hemophilia center. We tested for the presence of the Factor V Leiden mutation by PCR-amplifying a fragment of the factor V gene which contains the mutation site and then digesting the product with the restriction enzyme MnlI. None of the patients with hemophilia A and only one patient with hemophilia B was heterozygous for Factor V Leiden. None of the 21 patients had hereditary deficiencies of antithrombin III, protein C, or protein S. Our results indicate that the milder bleeding diathesis that is occasionally seen among Italian hemophiliacs with factor levels that are less than 1 percent cannot be explained by the concomitant expression of a known prothrombotic defect.