Factor V Leiden
Factor V Leiden is a hypercoagulability disorder in which one of the
coagulation factors cannot be deactivated. It is a genetic disorder and
is believed to affect 3-5% of the population.
It is an autosomal dominant condition in which the 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, the cleavage site for protein C.
As factor V cannot be inactivated, it continues to facilitate production
of thrombin, and so thrombi form in the veins.
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Symptoms and signs
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 patients suffering from
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.