Objectives: To elucidate the association between a genetic polymorphism of the fibrinogen Bbeta-gene (G-455A) and plasma fibrinogen levels and myocardial infarction (MI), respectively. In addition, to explore potential synergistic gene-environment interactions involving this polymorphism--until now, these data were unavailable.
Design setting and subjects: This case-referent study of subjects aged 45-70 and living in Stockholm includes 834 men and 346 women with first-time MI and 1034 men and 494 women randomly chosen as referents from the population. The cases were identified between 1992 and 1994 at the 10 emergency hospitals in Stockholm County.
Main outcome measures: MI and plasma fibrinogen levels.
Results: Crude analyses associated a high level of plasma fibrinogen with an increased risk of MI in both men and women. However, the relative risk decreased after controlling for other risk factors. The multivariate-adjusted odds ratio (OR) (95% confidence interval) was 1.6 (1.2-2.3) for men and 1.5 (0.9-2.6) for women. Presence of the A allele at the G-455A polymorphic site indicated higher plasma fibrinogen levels than the presence of the G allele, but the difference was only statistically significant for male cases. The -455A allele was not associated with an increased risk of MI. Furthermore, there were no strong indications of synergistic interaction between the G-455A polymorphism and any of the environmental exposures considered.
Conclusions: In this large number of MI cases and referents, a high level of plasma fibrinogen was independently associated with increased risk of MI in men but not in women. The presence of the A allele at the G-455A polymorphism of the fibrinogen Bbeta-gene was not associated with increased risk of MI, and no synergistic gene-environment interactions were detected.