Glycoprotein Polymorphisms Research Articles

Clinical and Functional Consequences of Platelet Membrane Glycoprotein Polymorphisms

The last several years have seen an abundance of studies of genetic risk factors for vascular disease, and platelet glycoprotein (GP) polymorphisms have been a primary focus of this area of research. This article reviews GP receptor polymorphisms, particularly those on GPIa-IIa (integrin alpha2beta1), GPIb-IX-V, GPIIb-IIIa (integrin alpha(IIb)beta3), and GPVI, and summarizes clinical and functional studies that have attempted to clarify their roles in human disease. Our focus is on recent work relevant to thrombotic and hemostatic processes and advances in pharmacogenetics. We consider issues affecting our ability to derive firm conclusions from these studies, and discuss future directions in this rapidly evolving area.

Platelet glycoprotein Ia C807T, Ib C3550T, and IIIa Pl A1/A2 polymorphisms and ischemic stroke in young Taiwanese

Platelet plays a pivotal role in the pathogenesis of thrombotic cardiovascular diseases. Recently, the polymorphism of platelet glycoprotein (GP) genes has been reported to be associated with an increased risk for ischemic stroke. The purpose of this study is to evaluate the association between platelet GP genetic variants and ischemic stroke in young Taiwanese. We conducted a case-control study in 157 young ischemic stroke patients recruited between September 2001 and March 2003 and 157 age- and sex-matched controls. The genotypes of platelet GP Ia C807T, GP Ib C3550T, and GP IIIa Pl A1/A2 polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism. Student's t-test, chi-square test, and logistic regression modeling were used for data analyses. The GP Ia C807T CC, CT and TT genotype frequencies were similar between patients (50.3%, 43.9%, 5.7%) and controls (53.5%, 38.9%, 7.6%; p=0.58). There were no significant differences in GP Ib C3550T CC and CT genotype distributions between patients (91.1%, 8.9%) and controls (91.7%, 8.3%; p=0.84). Of all subjects, none carries GP IIIa Pl A2 mutation. In conclusion, platelet GP Ia C807T and GP Ib C3550T polymorphisms in our population are less common compared with Caucasians, and GP IIIa Pl A1/A2 genetic mutation is not found, and all of them are not associated with ischemic stroke in young Taiwanese.

The 121Q allele of the plasma cell membrane glycoprotein 1 gene predisposes to polycystic ovary syndrome

The K121Q polymorphism of the plasma cell membrane glycoprotein 1 gene was significantly associated with polycystic ovary syndrome (PCOS) susceptibility, the pooled genotype distribution (K121K vs. 121Q allele) having an odds ratio of 1.90 (95% confidence interval 1.11-3.26). This suggests that impaired insulin signaling is of etiologic importance in PCOS.

Association between the human alpha 2-Heremans Schmidt glycoprotein (AHSG) polymorphism and endometriosis

Many studies have been undertaken to identify the candidate genes for endometriosis with the conflicting data in various populations. To date, the genes responsible for development of endometriosis have not been defined. Recently, it has been demonstrated that the the alpha 2-Heremans Schmidt glycoprotein (AHSG) gene is expressed in the endometrium of endometriosis patients, and that endometriosis patients have high levels of AHSG in serum and peritoneal fluid. Genetic polymorphism of AHSG with two common alleles, AHSG 1 and AHSG 2 has been described on isoelectric focusing.

Association of genetic polymorphisms in the fibrinogen and platelet glycoprotein genes with unstable angina in Chinese patients.

Inherited predisposition has been associated with coronary artery disease (CAD) in the white population. The objective of this study was to investigate the association between the risk of unstable angina (UA) and genetic factors believed to be associated with an increased tendency toward thrombosis (the variable number of tandem repeats [VNTR] polymorphism of the platelet glycoprotein [GP] Ib alpha gene, Pl(A1/A2) of the platelet GP IIIa gene, 448G/A of the Bbeta fibrinogen gene and Thr312Ala of the Aalpha fibrinogen gene) in Chinese patients with UA. We performed a case/control study evaluating 69 Chinese patients (43 men, 26 women) with UA and 69 control subjects without CAD, individually matched for age and gender. The restriction fragment length polymorphism (RFLP) method was used to determine the genetic polymorphisms. The frequencies of GP Ib alpha C/B genotype and Bbeta fibrinogen 448A allele were higher in patients with UA (46.4 vs. 30.4%, odds ratio [OR] 1.977, 95% confidence interval [CI] 0.98-3.97, p = 0.054, and 49.3 vs. 20.3%, OR 3.816, 95% CI 1.797-8.103, p = 0.000, respectively). Only four subjects (two cases, two controls) with GP IIIa Pl(A2) allele were found, and there was no association between Aalpha fibrinogen Thr312Ala polymorphism and UA. Chinese patients with UA had increased frequencies of GP Ib alpha C/B genotype and Bbeta fibrinogen 448A allele. These data suggest that some genetic factors may influence the development of UA.

Effect of glycoprotein IIIa Pl A2 polymorphism on outcome of patients with stable coronary artery disease and effect of smoking

A polymorphism of glycoprotein IIb/IIIa has been associated with myocardial infarction and restenosis after percutaneous coronary intervention. The influence on outcome and the interaction of the Pl A1 genotype with classic risk factors for coronary artery disease (CAD) were characterized in patients with chronic CAD followed prospectively for 3 years. Pl A1 genotypes were assessed in 592 patients enrolled in the Medical, Angioplasty, or Surgery Study II, a randomized trial comparing treatments for patients with CAD and preserved left ventricular function. The incidence of the composite end point of cardiac death, myocardial infarction, and refractory angina requiring revascularization were determined in each genotype group. Risk was assessed with the Cox proportional-hazards model. The clinical characteristics and treatment of each genotype were similar. Although the composite end point tended to be more common in patients with the Pl A2 allele, only smokers with the Pl A2 allele had a significantly increased incidence of the composite end point (p = 0.01). Moreover, a 2.2-fold increased risk was apparent in smokers with the Pl A2 allele (p = 0.03). Thus, taken together, these data provide support for the interaction effect between smoking and the Pl A1 gene variant. Smokers with the Pl A2 polymorphism of platelet glycoprotein IIIa are at greater risk for subsequent cardiac events in stable coronary disease.

1159-190 Role of the 807 C/T polymorphism of glycoprotein Ia/IIa on platelet function following clopidogrel loading dose in patients undergoing coronary stenting

1159-190 Role of the 807 C/T polymorphism of glycoprotein Ia/IIa on platelet function following clopidogrel loading dose in patients undergoing coronary stenting

Invited commentary

Background. Although bleeding and thromboembolism remain major complications after implantation of ventricular assist devices (VADs), no standard anticoagulation protocols are available. Genetic polymorphism of platelet glycoprotein IIb/IIIa may contribute to the development of complications. The present study demonstrates a relationship between the PIA genotype and postoperative complications in patients implanted with pulsatile and axial flow VADs. Methods. The P1A genotype was determined in 41 consecutive patients treated with a VAD who received anticoagulation with phenprocoumon and aspirin. Pulsatile Novacor (Novacor Corp, Oakland, CA) and Berlin Heart VADs (Berlin Heart, Berlin, Germany) were implanted in 28 patients and the axial flow MicroMed DeBakey VAD (MicroMed Technology, Inc, Houston, TX) in 13. The relationship between the P1A genotype, the anticoagulation regime, and bleeding and thromboembolic events was analyzed. Results. There were no differences between patients with the A1A1 and A1A2 genotype regarding demographic characteristics, weight, or infection episodes. The international normalized ratio (INR), platelet activation tests, and doses of aspirin and dipyridamol before events were similar in both groups. Patients with the A1A1 genotype developed more bleeding complications (39% vs 0%, p = 0.021), while patients with the A1A2 genotype showed a tendency toward more thromboembolic events (13% vs 30%, p = 0.33). With regard to different types of VAD, patients with the axial flow DeBakey VAD and the A1A1 genotype developed significantly more bleeding complications (70% vs 0%, p = 0.033). Conclusions. In patients with a long-term VAD determination of P1A polymorphism and subsequent adjustment of the anticoagulation regime may lead to a reduction of bleeding and thromboembolic complications.

Clinical significance of PlA polymorphism of platelet GP IIb/IIIa receptors during long-term VAD support

Background Although bleeding and thromboembolism remain major complications after implantation of ventricular assist devices (VADs), no standard anticoagulation protocols are available. Genetic polymorphism of platelet glycoprotein IIb/IIIa may contribute to the development of complications. The present study demonstrates a relationship between the PlA genotype and postoperative complications in patients implanted with pulsatile and axial flow VADs. Methods The PlA genotype was determined in 41 consecutive patients treated with a VAD who received anticoagulation with phenprocoumon and aspirin. Pulsatile Novacor (Novacor Corp, Oakland, CA) and Berlin Heart VADs (Berlin Heart, Berlin, Germany) were implanted in 28 patients and the axial flow MicroMed DeBakey VAD (MicroMed Technology, Inc, Houston, TX) in 13. The relationship between the PlA genotype, the anticoagulation regime, and bleeding and thromboembolic events was analyzed. Results There were no differences between patients with the A1A1 and A1A2 genotype regarding demographic characteristics, weight, or infection episodes. The international normalized ratio (INR), platelet activation tests, and doses of aspirin and dipyridamol before events were similar in both groups. Patients with the A1A1 genotype developed more bleeding complications (39% vs 0%, p = 0.021), while patients with the A1A2 genotype showed a tendency toward more thromboembolic events (13% vs 30%, p = 0.33). With regard to different types of VAD, patients with the axial flow DeBakey VAD and the A1A1 genotype developed significantly more bleeding complications (70% vs 0%, p = 0.033). Conclusions In patients with a long-term VAD determination of PlA polymorphism and subsequent adjustment of the anticoagulation regime may lead to a reduction of bleeding and thromboembolic complications.

Association of the gene polymorphisms of platelet glycoprotein Ia and IIb/IIIa with myocardial infarction and extent of coronary artery disease in the Korean population.

Platelet membrane receptor glycoproteins (GP) are essential for the platelet activation process, and the genetic polymorphisms in the genes that encode platelet glycoproteins have been proposed to influence the risk of acute coronary syndrome and atherosclerosis. In this study, we investigated the role of GPIa, HPA-1 and HPA-3 polymorphisms as putative risk factors for myocardial infarction (MI) and the extent of coronary artery disease. We selected 1,073 subjects who underwent coronary angiography; 242 had normal or minimal coronary atherosclerosis, and 831 patients had significant coronary artery disease (CAD). The genotype was determined by the methods of single base extension for C807T/G873A polymorphisms of GPIa, and restriction fragment length polymorphism for HPA-1 and HPA-3. The C807T and G873A polymorphisms of GPIa showed complete linkage in the Korean population. For HPA-1 gene polymorphism, only the HPA-1a/a (PlA1/A1) genotype was observed in 192 selected subjects from our study population. The distribution of GPIa (C807T/G873A) and HPA-3 genotypes did not differ significantly between normal subjects and CAD subjects. No significant association between MI and both gene polymorphisms was present. However, for the subgroup analysis of young male patients whose age was less than 56 years, the genotype frequency of HPA-3b/b was significantly lower in patients with MI compared to patients without a history of MI (7.5% vs. 20.0%, p=0.04). The odds ratio for HPA-3 b homozygosity versus the HPA-3a carrier was 0.32 (95% CI, 0.10- 0.99, p=0.04). Conclusively, HPA-3 polymorphism was associated with MI in Korean individuals younger than 56 years of age, but other polymorphisms of GP, which we studied, were not associated with both the extent of coronary atherosclerosis or MI.

PlA polymorphism and platelet reactivity following clopidogrel loading dose in patients undergoing coronary stent implantation

The PlA polymorphism (Leu33Pro) of the platelet glycoprotein (GP) IIIa gene has been suggested to play an important role in coronary thrombosis. In vitro studies have shown differences for this polymorphism in platelet sensitivity towards antiplatelet drugs (aspirin and abciximab), suggesting a pharmacogenetic modulation. The aim of the study was to assess the modulatory effect of the PlA polymorphism on clopidogrel-induced antiplatelet effects in 38 patients undergoing coronary stent implantation receiving a 300 mg clopidogrel loading-dose. Platelet reactivity was assessed as GPIIb/IIIa activation and P-selectin expression in platelets stimulated with 2 micromol/l adenosine diphosphate using whole blood flow cytometry. The distribution of the homozygous PlA1/A1 and heterozygous PlA1/A2 genotypes were 74 and 26%, respectively. PlA2 carriers had a higher degree of GPIIb/IIIa activation (P = 0.05) and P-selectin expression (P = 0.02) during the overall study time course and a lower antiplatelet effect to a 300 mg clopidogrel loading-dose up to 24 h following intervention (P < 0.05). In conclusion, the Pl polymorphism of the GPIIIa gene modulates platelet reactivity towards clopidogrel front loading in patients undergoing coronary stenting. This suggests the need for individualized antithrombotic regimens to optimally inhibit platelet reactivity.

Nonarteritic anterior ischemic optic neuropathy is associated with a specific platelet polymorphism located on the glycoprotein Ibα gene

Objective To evaluate the association between platelet glycoprotein polymorphisms and the risks of single and second eye involvement with nonarteritic anterior ischemic optic neuropathy (NAION). Design Case–control study. Participants Ninety-two consecutive patients with NAION, 26 of whom had second eye involvement, and 145 controls who attended the eye clinic for nonvascular entities. Methods Polymerase chain reactions and restriction enzyme analyses were performed for genotyping 5 platelet glycoprotein polymorphisms on DNA extracted from whole blood. Main outcome measures Frequencies of the various platelet polymorphisms. Results One of the 5 platelet glycoprotein polymorphisms analyzed, the B allele of the glycoprotein Ibα variable number of tandem repeats (VNTR), was a significant independent risk factor for NAION, with an odds ratio of 4.25 and a 95% confidence interval of 1.67 to 10.82 ( P = 0.0026). All other platelet glycoprotein polymorphisms were similarly distributed in patients and controls. In addition, 9 of 16 patients who bore the VNTR B allele (56.3%) had second eye involvement, whereas among patients not harboring the VNTR B allele only 17 of 72 patients (23.6%) had second eye involvement ( P = 0.009). Moreover, second eye involvement occurred earlier in patients who bore the specific polymorphism. Conclusions The presence of the VNTR B allele of glycoprotein Ibα confers a significant risk for NAION and predisposes affected patients to second eye involvement.

Role of platelet glycoprotein polymorphisms in cardiovascular diseases.

Atherothrombosis is the leading cause of death in western countries. Major complications of atherothrombotic disease, which are responsible for a large burden of morbidity and mortality, are acute coronary syndromes, ischemic stroke, and peripheral occlusive disease. Plaque rupture, platelet adhesion, aggregation, and thrombosis may lead to unstable angina and may progress to myocardial infarction as well as to ischemic stroke. Platelet membrane glycoprotein receptors mediate crucial reactions in acute thrombosis and chronic processes of atherogenesis. The platelet glycoprotein GP IIb/IIIa, which is the most abundant platelet receptor, also represents the drug target of a novel class of anti-platelet drugs, which includes abciximab, tirofiban, and eptifibatide. The genes encoding the three major platelet glycoprotein receptors (GP Ib/IX/V, GP Ia/IIa, and GP IIb/IIIa) are subject to considerable genetic variability. This paper reviews how polymorphisms in the platelet glycoprotein receptors affect platelet function, susceptibility to atherothrombosis and its major complications including myocardial infarction, stroke, and complications following percutaneous coronary interventions, and individual variability of drug response. Recent data on platelet glycoprotein receptor polymorphisms as modifiers of drug action and as predictors of drug response offer the perspective of individualized drug treatment. Prospective studies will show whether this approach is useful or not. As the data reviewed here show clearly, future clinical trials should routinely take into account genetic susceptibility factors and modifiers, both for study design and for predefined patient stratification.

Resistance in vitro to low-dose aspirin is associated with platelet PlA1(GP IIIa) polymorphism but not with C807T(GP Ia/IIa) and C-5T kozak (GP Ibα) polymorphisms

ObjectivesWe investigated whether three platelet gene polymorphisms, PlA1/A2, C807T, and C-5T Kozak (encoding, respectively, for platelet membrane glycoproteins (GP) IIIa, GP Ia/IIa, GP Ibα), could contribute to the resistance to a low dose of aspirin (160 mg/day). BackgroundAspirin antiplatelet effect is not uniform in all patients, and the mechanism by which some patients are in vitro resistant to aspirin remains to be determined. However, it has been suggested that polymorphisms of platelet membrane glycoproteins might contribute to aspirin resistance. MethodsNinety-eight patients on aspirin (160 mg/day) for at least one month were enrolled. Aspirin resistance was measured by the platelet function analyzer (PFA)-100 analyzer; genotyping of the three polymorphisms was performed using a polymerase chain reaction-based restriction fragment-length polymorphism analysis. ResultsUsing a collagen/epinephrine–coated cartridge on the PFA-100, the prevalence of aspirin resistance was 29.6% (n = 29). Aspirin-resistant patients were significantly more often PlA1/A1(86.2%; n = 25) than sensitive patients (59.4%; n = 41; p = 0.01). Of the 29 patients, 25 were reevaluated after having taken 300 mg/day aspirin for at least one month. Only 11 patients still have nonprolonged collagen epinephrine closure time, and these were all PlA1/A1. No relation was found between resistance status and C-5T Kozak or C807T genotypes. ConclusionsPlatelets homozygous for the PlA1allele appear to be less sensitive to inhibitory action of low-dose aspirin. This differential sensitivity to aspirin may have potential clinical implications whereby specific antiplatelet therapy may be best tailored according to the patient's PlAgenotype.

Collagen platelet receptor polymorphisms integrin α2β1 C807T and GPVI Q317L and risk of ischemic stroke

Several polymorphisms of integrin alpha2beta1 and glycoprotein (GP) VI that may modify platelet-collagen interactions or subsequent signaling have been described. We conducted a case-control study involving 180 stroke patients and 172 controls to determine whether the alpha2 C807T and GPVI Q317L polymorphisms were associated with an increased risk of ischemic stroke. We found no statistically significant differences in the distribution of alpha2 C807T and GPVI Q317L in patients and controls overall or after stratification by etiological subtype. The GPVI 317QQ genotype was found to be over-represented in a subgroup of patients >/=60 years compared to corresponding controls. However, this association did not remain significant after adjustment for other cardiovascular risk factors. Our results do not support a role for the integrin alpha2 C807T and GPVI Q317L polymorphisms in the development of first-ever ischemic stroke. However, larger studies are required to confirm this.

K121Q PC-1 gene polymorphism is not associated with insulin resistance in a Spanish population.

To investigate the effect of the K121Q plasma cell membrane glycoprotein (PC-1) polymorphism on the components of the insulin resistance syndrome in a population-based nationwide multicenter study in Spain. The subjects of the study were 293 nonrelated adults (44.7% men and 55.3% women) ages 35 to 64 years randomly chosen from a nationwide population-based survey on obesity and related conditions, including insulin resistance and cardiovascular risk factors. Obesity-related anthropometric measurements included blood pressure, oral glucose tolerance test, lipid profile (total cholesterol, high-density lipoprotein- and low-density lipoprotein-cholesterol, and triglycerides), plasma leptin, insulin levels by radioimmunoassay, and insulin resistance (homeostasis model assessment). K121Q PC-1 genotypes were determined by restriction fragment-length polymorphism-polymerase chain reaction. Overall Q allele frequency was 0.14, with no differences between obese and nonobese individuals (0.15 vs. 0.13). After adjustment for sex, age, BMI, and degree of glucose tolerance, the Q allele was associated with high plasma leptin and triglyceride levels, but not with insulin resistance. The results showed that the K121Q PC-1 polymorphism in the Spanish population has no significant impact on insulin sensitivity.

Analysis of platelet membrane glycoprotein polymorphisms in Glanzmann thrombasthenia showed the French gypsy mutation in the αIIb gene to be strongly linked to the HPA-1b polymorphism in β3

We have tested the DNA of a large series of Glanzmann thrombasthenia patients for polymorphisms in platelet membrane glycoproteins. To our surprise, we noted a high prevalence of the HPA-1b allele of beta3, the minority allele in a normal population. This proved to be due to the presence of nine patients homozygous for the so-called French gypsy mutation (IVS15[ + 1]G-->A) in alphaIIb. Seven of these patients were homozygous for the HPA-1b alloantigen and the other two heterozygous HPA-1a/1b. As the alphaIIb and beta3 genes are both on chromosome 17, it is highly probable that the French gypsy mutation first arose on a chromosome encoding HPA-1b. For other adhesion receptors, no major differences were seen in the distribution of the A1, A2 and A3 alleles in the alpha2 gene, or in the Kozak or HPA-2 polymorphisms of GPIbalpha, suggesting that none of these alleles result in increased survival in Glanzmann thrombasthenia.

CLINICAL SIGNIFICANCE OF PIA POLYMORPHISM OF PLATELET GP IIb/IIIa RECEPTORS DURING LONG-TERM VAD SUPPORT

Background Bleeding and thromboembolic events remain major complications after the implantation of VADs. Genetic polymorphism of platelet glycoprotein IIb/IIIa may contribute to the development of complications. Methods The PIA genotype was determined in 41 consecutive VAD patients who received anticoagulation with phenprocoumon, ASS and dipirydamol. Pulsatile VADs of the type Novacor and Berlin Heart were implanted in 28 patients and the axial flow MicroMed DeBakey VAD in 13. The relationship between the PIA genotype, the anticoagulation regime and bleeding and thromboembolic events was analyzed. Results There are no differences between patients with the A1A1 and A1A2 genotype regarding demographic characteristics. The follow-up time was in A1A1 group 239 and in the A1A2 group 442 days. The INR, results of platelet activation tests and doses of ASS and dipirydamol before events were similar in both groups. Patients with the A1A1 genotype developed more bleeding complications (42% vs. 0%, p=0.017), while A1A2 genotype patients showed more thromboembolic events (40% vs. 10%, p= 0.047). Multivariate analysis showed no impact of type of VAD and significant impact only of the genotype (p<0.05) on the development of postoperative complications. Conclusion In patients with VADs determination of PIA polymorphism and corresponding adjustment of anticoagulation regime may lead to a reduction of bleeding and thromboembolic complications.

The K121Q Polymorphism of the PC-1 Gene Is Associated With Insulin Resistance but not With Dyslipidemia

To investigate the relationship of the K121Q polymorphism of the plasma cell glycoprotein 1 (PC-1) gene with insulin resistance, insulin secretion, and lipids and lipoproteins. Altogether, 110 normoglycemic subjects (group I) underwent a hyperinsulinemic-euglycemic clamp for evaluation of insulin sensitivity. The first-phase insulin secretion was determined by the intravenous glucose tolerance test (IVGTT) in a separate sample of 295 normoglycemic subjects (group II). The 121Q allele (genotypes K121Q and Q121Q) compared with the K121K genotype was related to higher fasting insulin levels (group I: 69.6 +/- 45.6 vs. 51.9 +/- 28.4 pmol/l [mean +/- SD], P = 0.050; group II: 66.6 +/- 38.8 vs. 53.8 +/- 26.6 pmol/l, P = 0.009). In group I, subjects carrying the 121Q allele compared with subjects with the K121K genotype had lower rates of whole-body glucose uptake (51.17 +/- 12.07 vs. 60.12 +/- 14.86 micro mol x kg(-1) x min(-1), P = 0.012) and nonoxidative glucose disposal (33.71 +/- 10.51 vs. 41.51 +/- 13.36 micro mol x kg(-1) x min(-1), P = 0.015) during the clamp. In group II, there was no significant difference between the 121Q allele carriers and subjects with the K121K genotype in total first-phase insulin secretion during the first 10 min of the IVGTT (2,973 +/- 2,224 vs. 2,520 +/- 1,492 pmol. l(-1). min(-1), P = 0.415). No association of the K121Q polymorphism with serum lipids and lipoproteins was found. In healthy normoglycemic Finnish subjects, the K121Q polymorphism of the PC-1 gene is associated with insulin resistance but not with impaired insulin secretion or dyslipidemia.

Association of C807T, Pl A, and −5 C/T Kozak genotypes with density of glycoprotein receptors on platelet surface

This study investigates whether three platelet glycoprotein (GP) polymorphisms, C807T in GP Ia, Pl A1/A2 in GP IIIa, and −5 T/C Kozak in GP Ibα gene, influence the density of the three important adhesion and activation receptors on the platelet surface. Fifty-four healthy donors were genotyped according to the three polymorphisms, and densities of the corresponding GPs were measured by flow cytometry. Our study confirmed the association between C807T polymorphism and platelet surface expression of GP Ia–IIa and GP Ia and demonstrated that the density of GP Ibα or GP IX is not associated with the Kozak polymorphism. Although the Pl A1/A2 polymorphism did not affect the expression of GP IIb–IIIa and GP IIIa on the platelet surface, flow-cytometric analysis employing murine monoclonal antibody SZ21 against GP IIIa can be applied to distinguish Pl A1/A1 and Pl A1/A2 polymorphism.