Alpha 2-macroglobulin 5 bp insertion/deletion polymorphism increases the risk of recurrent venous thromboembolism

Alpha 2-macroglobulin (A2M) is a protease inhibitor that has been reported to neutralize thrombin, which may decrease the risk of thrombosis. A 5-base pairs (bp) insertion/deletion polymorphism (rs3832852) at the splice acceptor site of exon 18 has been shown to affect the binding of A2M with proteases. However, the role of this important variant in A2M in recurrent VTE is unknown. We investigated the role of 5 bp insertion/deletion polymorphism in VTE recurrence in a follow up study. A2M 5 bp insertion/deletion polymorphism was genotyped in Malmö Thrombophilia Study (MATS, n = 1465, with follow up of ~10 years) by TaqMan Allelic Discrimination assay. Univariate Cox regression analysis showed that A2M polymorphism was significantly associated with higher risk of VTE recurrence (hazard ratio [HR] = 2.61, 95% confidence interval [CI] = 1.06–6.45, P = 0.037). This association remained significant (HR = 2.61, 95% CI = 1.06–6.47, P = 0.038) even after adjusting for sex, family history of VTE, thrombophilia and acquired risk factors for VTE. In conclusion, our results indicate that patients with A2M 5 bp insertion/deletion polymorphism are at significantly higher risk of VTE recurrence and this may predict VTE recurrence.