Introduction
The prevalence of a heterozygous mutation in either Factor V Leiden
(FVL) or prothrombin G20210A (PT-G20210A) is 5% or 2%, respectively,
in the Caucasian population. The prevalence of double-heterozygosity for
these mutations is estimated to be 0.1% in the Caucasian population and
may be as high as 5% in patients diagnosed with deep vein thrombosis
(DVT). Heterozygosity for FVL increases the risk of venous
thromboembolism (VTE) from 1:1 000 to 3-8:1 000 per year whereas
heterozygosity for PT-G20210A mutation has been shown to increase the
risk from 1:1 000 to 2-3:1 000 per year. Antiphospholipid antibody
syndrome (APS) is a rare autoimmune disorder with estimated prevalence
of 20-50 cases per 100 000 persons and most commonly presents in
adolescents and young adults. These common polymorphisms are well
established risk factors for VTE. More recently, there have been large
studies comparing the risk in patients who have double-heterozygous
states or multiple polymorphisms. One study found patients who are
heterozygous for both FVL and PT-G20210A have up to a 20-fold increased
risk for initial venous thromboembolism. The prevalence and associated
risk of double-heterozygosity for FVL/PT-G20210A and concurrent APS is
rare and not well-described.
This report aims to describe the diagnosis, treatment, and outcome for
the acute presentation of extensive lower extremity DVT and saddle
pulmonary embolism (PE) in a previously healthy 17-year-old Caucasian
male found to have multiple genetic risk factors for venous
thromboembolism.