Factor V Leiden is associated with an increased risk of developing an episode of
DVT (with or without a PE). Approximately 1
in every 1000 people will develop a
DVT or PE each year, and this increases from about 1 in 10 000 for those in their twenties to about 5 in 1000 for those in their seventies. Heterozygous factor V Leiden increases the risk of developing a first DVT by 5- to 7-fold (or 5 to 7 in 1000 people each year).