group in Leiden, The Netherlands, identified the most common underlying defect—a mutation in factor V that made it resistant to the action of activated protein C. The defect was called factor V Leiden, as genetic abnormalities are typically named after the place where they are discovered. Two years later, the same group described a common mutation in the prothrombin gene that caused elevation of prothrombin levels and a mild increase in thrombosis risk. It is suspected that other genetic abnormalities underlying familial thrombosis will in future be discovered through studies of the entire genetic code, looking for small alternations in genes. References External links Coagulopathies