FACTOR-V-LEIDEN, ACTIVATED PROTEIN-C RESISTANCE, AND RETINAL VEIN OCCLUSION

Background: Resistance to activated protein C (APC resistance) is a th rombophilic abnormality characterized by a normal plasma level of prot ein C and an inherited defect in the coagulative response. This condit ion is believed to be caused by a point mutation in factor V, the so-c alled factor V Leiden, and is inherited as an autosomal dominant trait . Purpose: A case-control study was carried out to evaluate the preval ence of APC resistance and factor V Leiden in patients with retinal ve in occlusion (RVO) and in control subjects. Methods: Eighty-four conse cutive RVO patients and 70 controls were tested for APC resistance wit h a commercial assay (Chromogenix), The first 30 patients and 47 contr ols were also studied for factor V Leiden, In addition, a repeat APC-r esistance test was performed in 40 RVO patients and in 9 controls with a second-generation assay done to compare the reliability and reprodu cibility of the tests. Results: Results of testing for APC resistance with the first-generation assay revealed positive results in 38 (45%) of the study patients and 6 (9%) of the controls. The difference in fr equencies of APC resistance in patients and controls was statistically significant (P < 0.0001). in the patients tested for factor V Leiden, one (3%) was a heterozygous carrier of the Arg506Gln mutation and one (2%) of the controls was a heterozygous carrier. No homozygous indivi duals were identified in either the study or the control groups. The d ifference in frequencies of factor V Leiden in study patients and cont rols was not statistically significant (P = 1). The repeat APC-resista nce assay using factor V-deficient plasma in 40 RVO patients and 9 con trols did not show any significant difference between study patients a nd controls or an association between APC resistance and the determina tion of the factor V Leiden mutant. Conclusion: The first-generation c ommercial assay for APC resistance is not a useful screening test. The molecular test for factor V Leiden is the only definitive method. Fur thermore, no significant association was found between factor V Leiden and retinal vein occlusion. Accordingly, routine testing for the pres ence of the factor V Leiden mutant is not advisable for patients with retinal vein occlusion.