Role of the M2 haplotype within the annexin A5 gene in the occurrence of pregnancy-related venous thromboembolism

OBJECTIVE: Knowledge about risk factors for venous thromboembolism (VTE) is still limited. A recently found haplotype within the natural anticoagulant protein annexin A5 (ANXA5) exerts an important modulating effect on gene expression. STUDY DESIGN: Eighty-three nonanticoagulated patients with a documented pregnancy-related VTE and 195 controls were investigated. The presence of the ANXA5 haplotypes was determined. RESULTS: Twenty-seven patients (32.5%) carried the M2 haplotype. Among them, 17 (63.0%) had a history of VTE in puerperium and 10 (37.0%) during pregnancy. The prevalence of the M2 haplotype was different as compared with that recorded among controls (odds ratio, 2.7; 95% confidence interval, 1.5-4.9, P < .001). A logistic regression analysis, correcting for potential confounders (age at which the thrombotic event occurred, factor V Leiden, and factor IIA20210 variants) showed a significant increase (odds ratio, 3.4; 95% confidence interval, 1.7-6.7) of the occurrence of VTE in carriers of the M2 haplotype as compared with noncarriers. CONCLUSION: The M2 haplotype within the ANXA5 gene may represent a new thrombophilic risk factor for pregnancy-related VTE.