Meta-analysis of the association of platelet glycoprotein IIIa PlA1/A2 polymorphism with myocardial infarction

Invited review: Pharmacogenetics of estrogen replacement therapy

There are a number of genetic factors that likely modulate both the beneficial and adverse effects of estrogen. An important domain of consideration is the relationship of estrogen and thrombosis risk. Gene polymorphisms among the key elements of the coagulation and fibrinolytic cascade appear to influence the effects of estrogen on risk for venous thromboembolic events and possibly arterial thrombosis as well. Emerging data also suggest that allelic variants in the estrogen receptor-alpha may modulate estrogen's effects, especially with respect to bone and lipid metabolism.

Pl(A2) polymorphism of beta(3) integrins is associated with enhanced thrombin generation and impaired antithrombotic action of aspirin at the site of microvascular injury

BACKGROUND

Mechanisms by which the Pl(A2) (Leu33Pro) polymorphism of beta(3) integrins could lead to an increased risk for coronary events are unclear. This study was designed to examine the effect of this polymorphism on blood coagulation.

METHODS AND RESULTS

In normal subjects (12 with Pl(A1A1), 9 with Pl(A1A2), and 3 with Pl(A2A2)), we evaluated the activation of prothrombin, factor V, and factor XIII and fibrinogen removal by quantitative immunoblotting; thrombin-antithrombin III complex generation using ELISA; and levels of fibrinopeptide A and B by high-performance liquid chromatography in blood collected every 30 seconds at sites of standardized microvascular injury before and after 7 days of aspirin ingestion (75 mg/d). Compared with the Pl(A1A1) subjects, the Pl(A2) carriers exhibited higher maximum rates of thrombin B-chain generation (by 31.6%; P=0.005), thrombin-antithrombin III complex generation (by 30.7%; P=0.003), fibrinogen consumption (by 31.3%; P=0.002), prothrombin consumption (by 26.1%; P=0.011), and activation of factor V (by 14.1%; P=0.033) and factor XIII (by 27.0%; P=0.012). In the Pl(A1A1) homozygotes, aspirin ingestion resulted in reductions in the velocity of thrombin B-chain formation (by 32.1%; P=0.007), prothrombin consumption (by 30.4%; P=0.018), factor Va generation (by 28.9%; P=0.014), fibrinogen removal (by 41.2%; P=0.001), and factor XIII activation (by 22.6%; P=0.026). In the Pl(A2) carriers, aspirin did not alter the velocity of all these processes. After aspirin ingestion, fibrinopeptide A and B concentrations in the last 30-second interval were significantly reduced, but only in the Pl(A1A1) subjects.

CONCLUSIONS

The presence of the Pl(A2) allele is associated with enhanced thrombin formation and an impaired antithrombotic action of aspirin, which might favor coronary thrombosis in the Pl(A2) carriers.

Interaction between smoking and the glycoprotein IIIa P1(A2) polymorphism in non-ST-elevation acute coronary syndromes

OBJECTIVES

The goal of this study was to determine the interaction between smoking and the glycoprotein IIIa P1(A2) polymorphism in patients admitted with non-ST-elevation acute coronary syndromes (ACS).

BACKGROUND

An increased incidence of the P1(A2) polymorphism in smokers presenting with ST-elevation acute myocardial infarction (AMI) has recently been reported. We, therefore, postulated that, as a consequence of this interaction, fewer smokers with the P1(A2) polymorphism would present with non-ST-elevation ACS.

METHODS

We performed a prospective cohort analysis of 220 white Caucasoid patients admitted with non-ST-elevation ACS fulfilling Braunwald class IIIb criteria for unstable angina who were stratified by smoking status.

RESULTS

There were twice as many nonsmokers as smokers. Nonsmokers compared with smokers were older (mean [SD]; 63.9 [11.2] vs. 57.6 [10.3]; p < 0.0001), more likely to have had a previous admission with unstable angina (24.3% vs. 13.2%; p = 0.051) and AMI (45.8% vs. 30.3%; p < 0.026), more likely to have undergone revascularization (24.3% vs. 1.8%; p = 0.028) and were more likely to be on aspirin on admission (60.4% vs. 44.7%; p = 0.026). The proportion of nonsmokers positive for the P1(A2) polymorphism was equivalent to that expected for this population but was significantly reduced in smokers (28.7% vs. 10%; Pearson chi-square = 9.09, p = 0.0026). In a logistic regression model, the odds ratio (OR) for being positive for the P1(A2) polymorphism was significantly reduced by smoking (OR [interquartile range]: 0.26 [0.11 to 0.62]; p = 0.0026).

CONCLUSIONS

There is a significant reduction in the P1(A2) polymorphism in smokers admitted with non-ST-elevation ACS compared with nonsmokers, which suggests an interaction between smoking and this polymorphism.

Platelet glycoprotein gene polymorphisms and risk of thrombosis: facts and fancies

Over the past several years, platelet glycoprotein gene polymorphisms have received increasing attention as possible inherited determinants of prothrombotic tendency. However, their role in genetic susceptibility to thrombotic disease remains controversial. The glycoprotein IIIa Leu33Pro amino acid substitution appears to be associated with a subtle effect on platelet thrombogenicity in vitro, but is not a major risk factor for arterial thrombotic disease among the general population. Evidence suggests that the glycoprotein IIIa Pro33 allele may be associated with increased risk of thrombotic events following coronary re-vascularization and possibly among younger subjects with atherosclerosis. The nucleotide 807T variant of glycoprotein Ia is associated with increased platelet glycoprotein Ia/IIa receptor density, collagen-induced platelet adhesion and an increased risk of early onset myocardial infarction and stroke. Evaluation of the roles of the glycoprotein Ibalpha Thr145Met and variable number of tandem repeat polymorphisms has been complicated by their lack of well-defined effects on platelet adhesive function and the strong linkage disequilibrium between the two sites. Future epidemiologic studies of platelet glycoprotein gene polymorphisms will require larger sample sizes and family based approaches to further elucidate clinically important associations with thrombotic disease, including gene-environment and gene-gene interactions. Other polymorphisms of potential functional significance within genes encoding platelet membrane proteins will undoubtedly be discovered. The challenge will be to integrate advances in platelet biology with molecular and genetic epidemiology to enhance our understanding of the genetic determinants of common, but etiologically complex thrombotic diseases.