Factor V LeidenRogier Bertina and Pieter Reitsma

Blood clotting is not normally a problem. It allows a scab to form on a wound, and it keeps you from bleeding to death from the slightest cut or scrape. But if something goes wrong, clotting can be disastrous. In some cases this kind of defect can lead to decreased blood coagulation coupled with an increased tendency to bleed (haemophilia). , but the reverse is also possible: some people have an increased tendency towards blood coagulation, which can lead to clots in the blood vessels. Blood coagulation is regulated by specific proteins. A genetic defect can occur in one of these proteins, including a defect in blood coagulation factor V (five).  People with this defect have an increased risk of blood clots.

Venous and other forms of thrombosis

The greater chance of developing blood clots makes these people very vulnerable to venous thrombosis (a clot in a vein, especially in the leg), as well as to pulmonary embolism, and to a lesser extent also to a heart attack or a cerebral infarction (a type of stroke). Pregnant women with this defect are at greater risk of having a miscarriage. A mild form of the defect occurs in about five per cent of the population (when the defect is in a single chromosome), while the serious form (when both chromosomes have the defect) occurs in roughly one in every 5,000 people. It is the most commonly occurring genetic cause of venous thrombosis: nearly one in five patients with venous thrombosis in Europe have this defect.

In 1994, Leiden biochemist Rogier Bertina and molecular medicine specialist Pieter Reitsma, working in close collaboration with clinicians, discovered the genetic cause of the defect in blood coagulation factor V. The work of Fritz Rosendaal, a Leiden professor of epidemiology and a Spinoza Prize winner, then provided an extensive use for the information they had discovered about Factor V in understanding the causes of venous thrombosis. Venous thrombosis is usually caused by a combination of different factors together, one of which can be the genetic aspect. Additional factors include being bedridden or remaining seated on long trips, other illnesses, surgical operations and the use of female hormones (such as birth control pills). These factors also play a role in causing a heart attack, especially when accompanied by additional risk factors like smoking. Thanks to this Leiden discovery, we have a more complete picture of what is going on with patients, especially when multiple people in a single family develop thrombosis, and what preventive measures they can take for the future.