The bleeding phenotype of people with hemophilia, as noted above, is primarily determined by the baseline factor activity measurable in plasma; however, variability in laboratory assay performance [12,13], along with other possible disease-modifying factors [14], may impact the phenotype of people with hemophilia, including the mutation in the coagulation factor gene, other genetic alterations, and polymorphisms in other genes of the hemostatic system (eg, FV Leiden or antithrombin) as well as genetic variability of inflammatory and immune response genes [15]. The gene discussed is F5; the disease is hemophilia.