[The concomitant presence of prohemorrhagic and thrombophilic changes in coagulation factor V: a severe defect of coagulant activity and homozygote resistance to activated protein C].

We describe the peculiar and concomitant presence of a severe coagulation defect predisposing to bleeding and a mutation associated with inherited thrombophilia. A 6-year-old boy had a severe deficiency in factor V procoagulant activity and antigen and yet remained asymptomatic. This paradox might be explained by the hypothesis of the simultaneous presence of a thrombophilic disorder that might have restored hemostatic balance. The boy was a homozygous carrier of the Arg506Gln mutation of coagulation factor V, that renders this factor resistant to inactivation by its naturally occurring inhibitor, activated protein C. The family members, none of whom had bleeding or thrombotic symptoms, were heterozygotes for either the bleeding or the thrombophilic defect. Despite the severity of the bleeding defect, the absence of bleeding symptoms in the boy can be explained by the hypothesis that any residual amount of factor V present in his plasma is resistant to inactivation by activated protein C.