What is Factor V Leiden?
Factor V Leiden is a blood clotting disorder.
It is not a disease.
Factor V is a protein that is needed for blood to clot properly.
Some people do not
have the normal Factor V protein.
Instead, they have an different form called
Factor V Leiden.
This is caused by a change
(mutation) in the gene for this protein.
The different gene that makes the Factor
V Leiden protein is inherited from one or
The Factor V Leiden protein is harder to “turn off” than the normal Factor V protein.
This makes blood clots more likely to
form, a condition called thrombophilia.
If you have Factor V Leiden, you have a
greater chance of developing blood clots.
Blood clots in the deep veins in your legs
(called deep vein thrombosis or DVT)
or in your lungs (called pulmonary embolus or PE) can be dangerous.
How does Factor V Leiden affect clotting?
When you are injured, your body stops bleeding by changing
liquid blood into a
plug (clot) that blocks the leaks in damaged blood vessels.
Your body has many different proteins that
do this work.
There needs to be a balance
of these proteins to make sure there is just enough clotting power:
not enough clotting power leads to bleeding problems
too much clotting power can lead to the formation of dangerous blood clots
Factor V is one of the proteins needed to make blood form
The clotting action of
Factor V is controlled by another protein ca
lled Activated Protein C.
To stop blood
from forming clots, Activated Protein C easily turns off Factor V.
Activated Protein C does not work as well on
the abnormal Factor V Leiden protein.
Factor V Leiden resists the effects of Activat
ed Protein C, so it takes longer to turn off
Factor V Leiden.
As a result, clotting goes on
longer than usual. This is why Factor V
Leiden is sometimes called Activated Protein C Resistance and why people with this
mutation clot more than those without it.