Background Five classic thrombophilias have been recognized: factor V Leiden (rs6025), the prothrombin G20210A variant (rs1799963), and protein C, protein S, and antithrombin deficiencies. This study aimed to determine the thrombotic risk of classic thrombophilias in a cohort of middle-aged and older adults. Methods and Results Factor V Leiden, prothrombin G20210A and protein-coding variants in the PROC (protein C), PROS1 (protein S), and SERPINC1 (antithrombin) anticoagulant genes were determined in 29 387 subjects (born 1923-1950, 60% women) who participated in the Malmö Diet and Cancer study (1991-1996). The Human Gene Mutation Database was used to define 68 disease-causing mutations. Patients were followed up from baseline until the first event of venous thromboembolism (VTE), death, or Dec 31, 2018. Carriership (n=908, 3.1%) for disease-causing mutations in the PROC, PROS1, and SERPINC1 genes was associated with incident VTE: Hazard ratio (HR) was 1.6 (95% CI, 1.3-1.9). Variants not in Human Gene Mutation Database were not linked to VTE (HR, 1.1; 95% CI, 0.8-1.5). Heterozygosity for rs6025 and rs1799963 was associated with incident VTE: HR, 1.8 (95% CI, 1.6-2.0) and HR, 1.6 (95% CI, 1.3-2.0), respectively. The HR for carrying 1 classical thrombophilia variant was 1.7 (95% CI, 1.6-1.9). HR was 3.9 (95% CI, 3.1-5.0) for carriers of ≥2 thrombophilia variants. Conclusions The 5 classic thrombophilias are associated with a dose-graded risk of VTE in middle-aged and older adults. Disease-causing variants in the PROC, PROS1, and SERPINC1 genes were more common than the rs1799963 variant but the conferred genetic risk was comparable with the rs6025 and rs1799963 variants.
Keywords: epidemiology; genetics; natural anticoagulants; thrombophilia; venous thromboembolism.