Congenital factor V (FV) deficiency is a bleeding disorder associated with mild to severe hemorrhagic symptoms and a prevalence in the general population of 1 in 1,000,000 in the homozygous form. Patients with FV deficiency and clinically significant manifestations (mainly involving mucosal tracts) show very low or unmeasurable plasma FV levels and are usually homozygous or compound heterozygous for mutations located in the FV gene ( F5). Heterozygous carriers have approximately half-normal levels of FV and are usually asymptomatic. Replacement therapy for FV-deficient patients can only rely on administration of fresh-frozen plasma because specific FV concentrates are unavailable and FV is not present in cryoprecipitate or prothrombin complex concentrates. A total of 56 mutations have been published to date as being responsible for severe or moderately severe FV deficiency; more than two thirds of these are null mutations (mainly decreasing FV expression), with the remaining being missense mutations (usually impairing FV secretion). This article will provide a concise description of the FV protein and gene and will review the molecular, clinical, and therapeutic aspects of FV deficiency.
