Factor V Leiden (rs6025 or F5p.R506Q[1]) 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 that normally inhibits the pro-clotting activity of factor V, is not able to bind normally to factor V, leading to a hypercoagulable state, i.e., an increased tendency for the patient to form abnormal and potentially harmful blood clots.[2] Factor V Leiden is the most common hereditary hypercoagulability (prone to clotting) disorder amongst ethnic Europeans.[3][4][5] It is named after the Dutch city of Leiden, where it was first identified in 1994 by Rogier Maria Bertina under the direction of (and in the laboratory of) Pieter Hendrik Reitsma.[6] Despite the increased risk of venous thromboembolisms, people with one copy of this gene have not been found to have shorter lives than the general population.[7] It is an autosomaldominantgenetic disorder with incomplete penetrance.
^Ridker PM, Miletich JP, Hennekens CH, Buring JE (1997). "Ethnic distribution of factor V Leiden in 4047 men and women. Implications for venous thromboembolism screening". JAMA. 277 (16): 1305–7. doi:10.1001/jama.277.16.1305. PMID9109469.