title: Factor V Leiden, activated protein C resistance, and retinal vein occlusion.
abstract: BACKGROUND
  Resistance to activated protein C (APC resistance) is a thrombophilic abnormality characterized by a normal plasma level of protein C and an inherited defect in the coagulative response. This condition is believed to be caused by a point mutation in factor V, the so-called factor V Leiden, and is inherited as an autosomal dominant trait.
  
  
  OBJECTIVE
  A case-control study was carried out to evaluate the prevalence of APC resistance and factor V Leiden in patients with retinal vein occlusion (RVO) and in control subjects.
  
  
  METHODS
  Eighty-four consecutive RVO patients and 70 controls were tested for APC resistance with a commercial assay (Chromogenix). The first 30 patients and 47 controls were also studied for factor V Leiden. In addition, a repeat APC-resistance test was performed in 40 RVO patients and in 9 controls with a second-generation assay done to compare the reliability and reproducibility 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 frequencies 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 Arg506GIn mutation and one (2%) of the controls was a heterozygous carrier. No homozygous individuals were identified in either the study or the control groups. The difference in frequencies of factor V Leiden in study patients and controls was not statistically significant (P = 1). The repeat APC-resistance assay using factor V-deficient plasma in 40 RVO patients and 9 controls did not show any significant difference between study patients and controls or an association between APC resistance and the determination of the factor V Leiden mutant.
  
  
  CONCLUSIONS
  The first-generation commercial assay for APC resistance is not a useful screening test. The molecular test for factor V Leiden is the only definitive method. Furthermore, no significant association was found between factor V Leiden and retinal vein occlusion. Accordingly, routine testing for the presence of the factor V Leiden mutant is not advisable for patients with retinal vein occlusion.
authors.affiliation: LuEsther T. Mertz Retinal Research Department, Manhattan Eye, Ear, and Throat Hospital, New York, New York 10021, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Ciardella
authors.forename: L A
authors.initials: LA
authors.lastname: Yannuzzi
authors.forename: K B
authors.initials: KB
authors.lastname: Freund
authors.forename: D
authors.initials: D
authors.lastname: DiMichele
authors.forename: M
authors.initials: M
authors.lastname: Nejat
authors.forename: J T
authors.initials: JT
authors.lastname: De Rosa
authors.forename: J R
authors.initials: JR
authors.lastname: Daly
authors.forename: L
authors.initials: L
authors.lastname: Sisco
mesh_terms: D020016:Activated Protein C Resistance / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004252:DNA Mutational Analysis; D005165:Factor V / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010314:Partial Thromboplastin Time; D017354:Point Mutation; D015995:Prevalence; D011486:Protein C / Q000378:metabolism; D015203:Reproducibility of Results; D012170:Retinal Vein Occlusion / Q000378:metabolism*
chemical_list: D011486:Protein C; C095381:factor V Leiden; D005165:Factor V