• factor V;
  • coagulation;
  • platelets;
  • polymorphisms;
  • discovery

Summary.  The paper tells the story of how FV was discovered in 1943 and installed into the Morawitz theory, a dogma that had reigned the clotting field since 1905 without serious challenges. It is a witness to the fact, many times experienced throughout scientific history, that seminal achievements may arise from serendipity under awkward conditions. Under the worst of circumstances, only a brilliant mind, scientific curiosity and devotion, could the challenge Owren met in Mary's bleeding problem, lead to such a pivotal result. On top of establishing a new clotting factor, his work spurred an unprecedented activity in the field.

The thorny road to the new factor's place and role in the clotting mechanism is depicted in some detail. But the factor turned out to be more capricious than its role in coagulation seemed to indicate. Thus, in recent times it has become clear that its platelet counterpart plays an additionally important role in hemostasis as a whole. The two polymorphisms of clinical importance discovered in platelet FV lead to a bleeding disorder, whereas one in plasma FV leads to a rather frequent venous thromboembolic state. Further surprises might therefore be expected from this chameleon of a factor – reflecting the increasingly appreciated tendency that one biological compound appears in different roles.