Thrombophilia is a blood clotting disorder that increases the risk of developing blood clots in the blood vessels. One of the most common causes of inherited thrombophilia is factor V Leiden. Learn about the symptoms, causes and management of FVL.
Key points
Factor V Leiden (FVL) increases the chance of developing a blood clot such as a deep vein thrombosis (DVT) or a pulmonary embolism (PE). DVT occurs in the deep veins of the arms or legs, while a PE is a clot that travels to the lungs.
Diagnosis of FVL occurs through a simple blood test.
Although there is no direct treatment for the FVL mutation, preventative measures like exercise, a healthy diet, and avoiding smoking and/or alcohol consumption, are some ways that the risk for developing blood clots can be reduced.
Introduction
What is Factor V Leiden?
Factor V Leiden (FVL) is a blood clotting disorder caused by a change in the factor V (5) gene.
Clotting factors, such as factor V, are proteins in the blood that help to stop cuts and wounds from bleeding. Platelets, one of the main elements in blood, work together with the clotting factors to stop bleeding by creating blood clots. Blood clots are clumps of blood, including clotting factors and platelets, which harden over time to stop wounds from bleeding. Once the bleeding is controlled, the blood clot stops growing.
In people with FVL thrombophilia, coagulation factor V cannot be stopped normally. This means the clotting process continues longer than usual, which increases the chance of developing abnormal blood clots.
FVL is more frequently seen among people of northern European descent.
Signs and symptoms
What are the signs and symptoms of factor V Leiden?
The FVL gene mutation itself does not cause any signs and symptoms. However, if your child develops a blood clot, they will have symptoms related to the clot. Signs and symptoms will depend on where in the body the blood clot is.
Deep vein thrombosis (DVT) is a blood clot in the deep veins of the arms or legs. Signs and symptoms of DVT include:
Pain
Limb swelling
Redness
Warmth
Deep vein thrombosis (DVT)Normally, blood flows easily through the deep veins of the body with the help of both vein valves and muscle contractions. Although less common than in adults, a child might also get a blood clot in a deep vein. The blood clot (thrombus) can fill the inside of the vein obstructing blood flow.
A pulmonary embolism (PE) is a blood clot that has broken off from a larger blood clot and travelled to the lung. Signs and symptoms of PE include:
Chest pain
Shortness of breath
Blood while coughing
Fainting
Pulmonary embolism1) A small piece of a fresh blood clot in a vein can break free (embolus). 2) The embolus travels through the veins of the body to the heart and into the lung. 3) The embolus gets stuck in a blood vessel in the lung. This blocks blood flow to a part of the lung.
Causes, risk factors and prevalence
What causes factor V Leiden?
The FVL mutation can be inherited from one or both parents. The type of FVL a person has depends on whether they inherited one gene from one parent, or one gene from each parent.
Homozygous mutation
When a copy of the FVL gene mutation is inherited from one parent, and another copy of the FVL gene mutation from the other parent, this is called homozygous FVL. It affects less than 1% of the population. The inheritance pattern of the mutation is shown below:
Homozygous inheritanceInheritance of factor V Leiden when both parents are heterozygous.
Heterozygous mutation
Heterozygous mutations are seen in between 5-8% of the population. A mutated copy of the factor V gene is inherited from one parent and a normal copy of the gene from the other parent, as seen below:
Heterozygous inheritance with heterozygous parentInheritance of factor V Leiden when one parent is heterozygous. This is the most common type of inheritance.Heterozygous inheritance with homozygous parentInheritance of factor V Leiden when one parent is homozygous.
Risk factors of blood clots in people with factor V Leiden
The FVL mutation slightly increases the risk of developing blood clots in the veins. In people with heterozygous FVL, the risk of thrombosis is increased 5-7 times. In homozygous FVL, the risk increases 25-50 times. However, it is important to stress that the incidence of blood clots in children is quite rare, occurring at 0.07–0.14 per 10,000 children. As a person ages, their chance of developing a blood clot increases. The figure below shows the increasing frequency of blood clots with age.
Frequency of blood clots with ageAs a person gets older, their chance of developing a blood clot increases exponentially.
Diagnosis
How is factor V Leiden diagnosed?
To diagnose FVL, a blood sample is taken for genetic testing.
Treatment
How is factor V Leiden managed?
There is no direct treatment for FVL disorder. Instead, the goal of management is to minimize the risk of getting a blood clot in the first place. Risk factors for developing blood clots include:
Obesity
Immobility
Cancer and chemotherapy
Surgery or trauma
Dehydration
Catheters
Pregnancy
Use of oral contraceptives or hormone therapies
Smoking
The following measures may be taken to prevent blood clots:
Maintain a healthy diet. Talk to your child’s health-care team before changing your child’s diet and follow Canada’s Food Guide where applicable. Any irregular weight gain can contribute to the poor circulation of blood in the veins, increasing the risk of blood clots.
Smoking and binge drinking or excessive alcohol consumption should be avoided.
When travelling, encourage your child to walk around whenever possible. Decreased circulation of blood flow can increase the risk for blood clots.
Encourage your child to get regular physical activity. Children and youth typically need at least 60 minutes of moderate-to-vigorous intensity physical activity every day.
If a child with FVL needs to take hormonal therapy (e.g., birth control pills), talk to a gynecologist about how they can be safely taken, in order to help reduce the risk of blood clots.
When to seek medical attention
When to seek medical attention
If you suspect your child has developed a blood clot, call their doctor immediately. If you cannot reach the doctor, take your child to the nearest emergency department.
For more information on thrombophilia, thrombosis, post-thrombotic syndrome and the management of these conditions, please visit the
Thrombosis Learning Hub.
References
References
RH White. The Epidemiology of Venous Thromboembolism.
Circulation. 2003;107:I-4-I-8
