Factor V Leiden – Wikipedia

Factor V Leiden (rs6025 or F5 p.R506Q) is a variant (mutated form) of human factor V (one of several substances that helps blood clot), which causes an increase in blood clotting (hypercoagulability).Due to this mutation, protein C, an anticoagulant protein which normally inhibits the pro-clotting activity of factor V, is not able to bind normally to factor V, leading to a hypercoagulable …

https://en.wikipedia.org/wiki/Factor_V_Leiden