This study examined the influence of the Pl A polymorphism of glycoprotein IIIa (GPIIIa) in determining the response to an oral GPIIb/IIIa antagonist, orbofiban, in patients with unstable coronary syndromes. Genotyping for the Pl A polymorphism was performed in 1014 patients recruited into the OPUS-TIMI-16 (orbofiban in patients with unstable coronary syndromes-thrombolysis in myocardial infarction 16) trial, in which patients were randomized to low-or high-dose orbofiban or placebo for 1 year. The primary end point (n ‫؍‬ 165) was a composite of death, myocardial infarction (MI), recurrent ischemia requiring rehospitalization, urgent revascularization, and stroke.Overall, orbofiban failed to reduce ischemic events when compared with placebo, but increased the rate of bleeding. In the whole population, Pl A2 carriers had a significant increase in MI (n ‫؍‬ 33) during follow up, with a relative risk (RR) of 2.71 (95% CI, 1.37 to 5.38; P ‫؍‬ .004). There was a significant interaction between treatment (placebo and orbofiban) and the Pl A polymorphism for bleeding (n ‫؍‬ 187; P ‫؍‬ .05). Thus, while orbofiban increased bleeding in noncarriers (RR ‫؍‬ 1.87, 1.29 to 2.71; P < .001) in a dose-dependent fashion, it did not increase bleeding events in Pl A2 carriers (RR ‫؍‬ 0.87, 0.46 to 1.64). There was no interaction between treatment (placebo and orbofiban) and the Pl A polymorphism for the primary end point (P ‫؍‬ .10). However, in the patients receiving orbifiban there was a higher risk of a primary event (RR ‫؍‬ 1.55, 1.03 to 2.34; P ‫؍‬ .04) and MI (RR 4.27, 1.82 to 10.03; P < .001) in Pl A2 carriers compared with noncarriers. In contrast, there was no evidence that Pl A2 influenced the rate of recurrent events in placebo-treated patients. In patients presenting with an acute coronary syndrome, the Pl A polymorphism of GPIIb/IIIa may explain some of the variance in the response to an oral GPIIb/IIIa antagonist. IntroductionPlatelet activation and subsequent aggregation play major roles in initiating coronary thrombosis, the underlying event in acute coronary syndromes such as unstable angina and myocardial infarction (MI). Platelet aggregation is mediated by glycoprotein (GP) IIb/IIIa, the receptor for fibrinogen and von Willebrand factor (vWf). GPIIb/IIIa antagonists bind to the receptor and prevent platelet aggregation to all known agonists. Yet oral GPIIb/IIIa antagonists have proven ineffective and may be harmful when administered chronically to patients presenting with acute coronary syndromes. 1 Three large-scale clinical trials have reported an increase in death and MI in patients on active treatment compared with placebo. In the OPUS-TIMI-16 (orbofiban in patients with unstable coronary syndromes-thrombolysis in myocardial infarction 16) trial of orbofiban, the study was terminated due to an increase in mortality. 2 In the SYMPHONY II (sibrafiban versus aspirin to yield maximum protection from ischemic heart events post-acute coronary syndromes II) trial, 3 there was an increase in MI and death in patien...

Summary Some studies have suggested that genetic variability in the glycoprotein (GP) IIIa gene modulates expression of platelet GPIIb/IIIa (α2bβ3). We sought to determine as to whether combinations of genetic variants within the GPIIIa gene (haplotypes) influenced the expression of GPIIIa RNA and protein levels in human platelets. Three promoter polymorphisms, PlA1/A2 genotype and platelet receptor densities were determined in 207 acute coronary syndrome (ACS) patients. Allele‐specific quantitative reverse transcription‐polymerase chain reaction of platelet RNA from PlA1/A2 heterozygotes identified a greater expression of PlA2 bearing transcripts among heterozygotes. Among the patients studied, the ratio of PlA1/PlA2 RNA expression was significantly influenced by promoter haplotype (P < 0·01). However, this effect reflected carriership of rare not common haplotypes (P = 0·2). There was a threefold variation between subjects in the number of GPIIb/IIIa receptors expressed per platelet, although no association between receptor density and the PlA2 (P = 0·93) or promoter polymorphisms was demonstrated (−468A, P = 0·52; −425C, P = 0·59; −400A, P = 0·52). Among common haplotypes, PlA1/PlA2 RNA expression was negatively correlated with adjusted GPIIb/IIIa receptor density (P = 0·04). The overall trend towards higher expression of PlA2 bearing message in PlA1/A2 heterozygotes, and the existence of rare haplotypes with more pronounced changes indicate the existence of cis‐acting genetic factors that remain to be identified.

SummaryScreening for the PlA polymorphism has been made faster and simpler with the advent of heteroduplex technology. Simultaneous screening for three common prothrombotic polymorphisms PlA, factor V Leiden, and MTHFR(C677T) has been achieved with multiplex heteroduplex analysis. We describe a quick and simple method for PlA heteroduplex probe production. The probe was multiplexed with heteroduplex probes for MTHFR(C677T) and factor V Leiden polymorphisms in a one tube assay, allowing rapid automated genotyping of all three. This automated multiplex assay was applied to a cohort of 165 patients and showed excellent correlation with gel-based assays, both PAGE and RFLP. This approach will facilitate the analysis of multiple polymorphisms in complex disease in large populations.