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.