Influence of the -675 4G/5G dimorphism of the plasminogen activator inhibitor 1 promoter on thrombotic risk in patients with factor V Leiden

Elevated plasminogen activator inhibitor 1 (PAI-1) levels are associated with venous thromboembolism, although their significance is unclear. PAI-1 levels are influenced by a PAI-1 promoter dimorphism (4G/5G), the 4G allele being associated with increased PAI-1 activity. We investigated whether the 4G allele influenced thrombotic risk by studying 99 symptomatic factor V (FV) Leiden heterozygotes and 99 healthy subjects. The 4G allele was more prevalent among cases than among healthy subjects (chi2 = 8.00, P = 0.005) and the odds ratio (OR) for thrombosis associated with either heterozygosity or homozygosity for the 4G allele was 2.43 (P = 0. 011). We conclude that carriership of the 4G allele was more prevalent in patients who already carried factor V Leiden than in control subjects without factor V Leiden.