Factor V Leiden

Factor V Leiden is a hypercoagulability disorder where one of the coagulation factors cannot be deactivated. It is a genetic disorder, and 3-5% of the population is believed to have this condition.

Factor V Leiden is an autosomal dominant condition, where this coagulation factor has a mutation and cannot be destroyed by activated protein C[?] (aPC). The actual point mutation causes an arginine to be replaced with a glutamine, at the 506th amino acid. This is a cleavage site for protein C.

As factor V cannot be inactivated, it continues to assist in the production of thrombin, and so thrombi form in the veins.

Up to 30% of patients who present with venous thrombosis, or pulmonary embolism have this mutation.

This disease can be diagnosed by watching the APTT[?] (the time it takes for blood to clot) as activated protein C is added. With a normal patient, adding aPC increases the APTT. With Factor V Leiden, adding aPC will barely affect the time it takes for blood to clot.

There is also a simple genetic test that can be done for this disorder. The mutation (a 1691G→A substitution) removes a cleavage site of the restriction endonuclease[?] MnlI, so simple PCR, treatment with MnlI, and then DNA electrophoresis will give a quick diagnosis.