<p>Factor V is an essential protein in the blood clotting process and plays a central role in secondary hemostasis. Its deficiency causes a rare inherited disorder characterized by episodes of severe bleeding, some of which can be life-threatening. Although previous studies have established that factor V is essential for normal embryonic development, its specific contribution to vascular maturation remains incompletely understood, factor V is believed to contribute to blood vessel stabilization and regulate angiogenesis through its interaction with thrombin. In a recent study, a CRISPR-engineered mouse model intended to produced a mild factor V deficiency disease, unexpectedly produced a frameshift mutation in the A3 domain, resulting in a truncated protein. Factor V levels in healthy embryonic mouse tissues were assessed to investigate its role at different developmental stages. The mutation markedly impaired viability, as homozygous mice exhibited a lethal phenotype with severe bleeding and perinatal death, along with impaired coagulation function. Histopathological and immunohistochemical analyses indicated a link between factor V deficiency, thrombin and α-smooth muscle actin, potentially affecting proangiogenic signaling and embryonic vascular formation. Factor V gene expression increased during late embryogenesis, underscoring its importance in vascular development and maturation. Overall, these findings are consistent with a role for factor V in stabilizing embryonic blood vessels and modulating thrombin-dependent angiogenesis, and add further detail on the developmental impact of its deficiency and the pathogenesis of congenital bleeding disorders.</p>