Heritable thrombophilia and hypofibrinolysis. Possible causes of retinal vein occlusion.

Abstract

To determine whether heritable thrombophilia and hypofibrinolysis were risk factors for retinal vein occlusion. Measures of thrombophilia (increased likelihood of thrombus formation) included anticardiolipin antibodies (IgG and IgM), the lupus anticoagulant (including dilute Russell viper venom clotting time), antigenic proteins C and S, and homocysteine. Polymerase chain reaction assays were performed for 3 thrombophilic gene mutations (factor V Leiden, methylenetetra-hydrofolate reductase, and prothrombin gene). Measures of hypofibrinolysis (reduced ability to lyse thrombi) included lipoprotein Lp(a), plasminogen activator inhibitor activity, and polymerase chain reaction analysis of the hypofibrinolytic 4G/5G polymorphism of the PAI1 gene. These coagulation measures were performed in 17 patients with retinal vein occlusions with comparison with serologic coagulation measures and polymerase chain reaction assays in 40 and 234 healthy normal volunteers as controls, respectively. Of 14 patients with retinal vein occlusion with measures of dilute Russell viper venom clotting time, a thrombophilic antiphospholipid antibody, 6 (43%) had abnormal results (> 38.8 seconds) compared with 1 (3%) of 30 controls (P = .002). Of 17 patients with vein occlusion, 3 (18%) were heterozygous for the thrombophilic factor V Leiden G1691A mutation compared with 7 (3%) of 233 controls (P = .02). Of 17 patients with vein occlusion, 2 (12%) had normal alleles (5G/5G) for the plasminogen activator inhibitor gene promoter; the other 15 (88%) were heterozygous or homozygous for the 4G polymorphism, which is associated with hypofibrinolysis. Of 234 controls, 85 (36.3%) had the 5G/5G allele; 149 (63.7%) were heterozygous or homozygous for the 4G polymorphism (P = .03). Patients with vein occlusion were more likely to have high levels of the major determinant of hypofibrinolysis, plasminogen activator inhibitor activity. These levels were high (> 22 U/L) in 6 (38%) of 16 patients with vein occlusion compared with 1 (2%) of 40 controls (chi 2 = 12.8; P = .001). Patients with vein occlusion were more likely (8/16 [50%]) to have high levels of hypofibrinolytic Lp(a) (> 35 mg/dL) than controls (5/40 [13%]; chi 2 = 9; P = .003). The median Lp(a) level in patients with vein occlusion who had the 4G/4G genotype was 62 mg/dL compared with 5.3 mg/dL in controls with the 4G/4G genotype (P = .05). Thrombophilia and hypofibrinolysis are possible causes of retinal vein occlusion.