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Described by Bertina et al in 1994, it is an autosomal dominant condition in which the coagulation factor has a mutation and cannot be destroyed by activated protein C (aPC). It is a single nucleotide substitution of adenine for guanine - which causes an amino acid substitution of glutamine for arginine at position 506, 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.
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 electrophoresisDNA electrophoresis is an analytical technique used to separate DNA fragments by dimension. It is an example of chromatography. Basically, an electric field forces the fragments to migrate in a gel. DNA molecules normally migrate from negative to positive will give a quick diagnosis.
Suspicion of factor V leiden being the cause for any thrombotic event should be considered in any white patient below the age of 45, or in any person with a family history of thrombosis.
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