Low factor V level ameliorates bleeding diathesis in patients with combined deficiency of factor V and factor VIII.

Combined factor V (FV) and FVIII deficiency (F5F8D) is a rare autosomal-recessive bleeding disorder caused by mutations in lectin mannose binding-1 (LMAN1) and multiple coagulation factor deficiency-2 (MCFD2). Six causative homozygous mutations (5 in LMAN1 and 1 in MCFD2) were identified in 6 patients with F5F8D. A thrombin-generation assay, triggered with tissue factor (1 pM) in F5F8D plasma, paradoxically exhibited enhanced thrombin generation compared with normal plasma. Significantly lower free tissue factor pathway inhibitor (fTFPI) was found in F5F8D patients compared with healthy controls (P < .01). Normalizing tissue factor pathway inhibitor α (TFPIα) in F5F8D plasma greatly delayed and reduced thrombin generation. Increasing FV concentrations by adding plasma FV to F5F8D plasma only caused a gradual decrease in thrombin generation, suggesting that low levels of TFPIα and FV cocontributed to the elevated thrombin generation by reducing anticoagulant effects. On the contrary, thrombin generation in F5F8D platelet-rich plasma (PRP) was significantly lower than in normal controls (P < .05); however, it was fully corrected by normalizing FVIII or after 1-deamino-8-d-arginine vasopressin (DDAVP) infusion, indicating that the hypocoagulable state of F5F8D patients is associated with low FVIII levels. In addition, plasma and platelet FV in F5F8D PRP were sufficient to support normal thrombin generation, and low TFPIα may have no effect on thrombin generation. DDAVP infusion induced a complete response in 5 F5F8D patients and a partial response in the remaining patient. Based on our findings, we suggest that DDAVP may be considered a potential substitute for FVIII concentrates, and fresh-frozen plasma (FFP) infusion may not be necessary for F5F8D patients with minor bleeding challenges.