The HR2 haplotype of factor V is not associated with the risk of myocardial infarction

The HR2 haplotype of the factor V gene, which contains the histidine to arg inine substitution at position 1299, has been reported to be associated wit h reduced factor V levels. Because high factor V levels have been found to be associated with an increased risk of myocardial infarction, we examined how the presence of the R2 allele affected the risk of myocardial infarctio n in the case-control "Study of Myocardial Infarctions Leiden". Among 560 men with a first myocardial infarction before the age of 70 years , 9.5% were heterozygous carriers of the R2 allele. The control group consi sted of 646 men, in which 9.9% were heterozygous and 0.2% homozygous carrie rs of the R2 allele. The risk of myocardial infarction in the presence of t he R2 allele was not increased (odds ratio, 0.9; 95% confidence interval 0. 6 to 1.4. Exclusion of factor V Leiden carriers did not change this result. The risk was 4.4-fold increased for smokers who carried the R2 allele comp ared to non-smoking noncarriers. No synergy was found between metabolic ris k factors and the presence of the R2 allele. We conclude that the risk of myocardial infarction for men in the presence of the R2 allele of the His1299Arg polymorphism is neither increased nor de creased.