The GPIa C807T dimorphism associated with platelet collagen receptor density is not a risk factor for myocardial infarction

GPla Polymorphisms Are Associated with Outcomes in Patients at High Cardiovascular Risk

Background

Platelet membrane glycoprotein receptors mediate thrombus formation. GP Ia/IIa is an essential platelet integrin receptor. Single-nucleotide polymorphisms (SNPs) of the GP Ia/IIa gene alter GP Ia/IIa expression; however, their influence on cardiovascular disease remains unclear. This study aimed to investigate the effect of the GP Ia/IIa SNPs rs1126643 and rs1062535 on clinical outcomes in a large collective including high-risk patients with cardiovascular disease.

Methods and results

GP Ia SNP analysis was performed in 943 patients with symptomatic coronary artery disease. All patients were tracked for all-cause death, myocardial infarction, and ischemic stroke for 360 days. Homozygous carriers of the minor allele showed significantly worse event-free survival when compared with major allele carriers in the complete collective as well as in the subset of high-risk patients (carrying all of the following three risk factors: diabetes type II, hypertension, and hyperlipidemia). There was no significant difference in the subset of low-risk patients (carrying none of the three risk factors).

Conclusions

GPla SNPs are associated with cardiovascular prognosis especially in high-risk patients. Identification of GPIa SNPs is of importance to tailor therapies in patients at already high cardiovascular risk.

Platelet Receptor HPA-1 Polymorphism of αIIbβ3 and 807 C/T Polymorphism of α2β1 and Buerger's Disease

Thromboangiitis obliterans or Buerger's disease is an episodic and segmental inflammatory and thrombotic process of the medium and small arteries of the lower extremities. Even though the disease was described 90 years ago, the etiopathogenesis is still under consideration. Afflicted patients are mostly young male cigarette smokers without signs of atherosclerosis or other risk factors for peripheral arterial occlusive disease. This indicates that hereditary thrombophilic factors could play a role in the etiopathogenesis. Recently, increasing evidence shows that platelet receptor polymorphisms (HPA-1 polymorphism of β3 subunit of αIIbβ3 and 807 C/T polymorphism α2β1) are associated with early onset of arterial thrombosis (myocardial infarction, stroke). This case-control study was designed to assess whether the 807 C/T polymorphism or the HPA-1 polymorphism is involved in the pathogenesis of Buerger's disease or has any influence on the clinical course of Buerger's disease. Eighteen patients with Buerger's disease and 81 (sex and age matched) healthy control subjects (mean age 44 ± 10 vs 45 8 years, respectively) were genotyped for platelet receptor HPA-1 and GPIa 807 C/T polymorphism. The gene frequency of HPA-1 and GPIa 807 C/T polymorphisms was identical in both groups. Prevalence of hetero- and homozygous carriers of the HPA-1b allel (1a1b and 1b1b genotype) as well as the prevalence of the 807 C/T and 807 T/T carriers did not differ significantly between the two groups, p >0.05. The grade of clinical disease manifestation as well as disease progression did not reveal any significant relationship with HPA-1 and 807 C/T polymorphisms. A relationship between the age at onset of the disease and HPA-1 polymorphism was not found. Otherwise analysis of the GPIa 807 C/T platelet receptor polymorphism showed that the average age of patients who are carriers of the T allele at early onset of disease was 32 ± 6 years (range 27—48 years) compared to 42 ± 6 years (range 34—53 years) of the C/C carriers (p <0.05). This indicates that the GPIa 807 C/T polymorphism does not represent a risk factor for Buerger's disease itself, but could be associated with premature onset of this disorder in predisposed individuals.

Idiopathic sudden sensorineural hearing loss: classic cardiovascular and new genetic risk factors

BACKGROUND

The main causative process in idiopathic sudden sensorineural hearing loss (iSSNHL) has yet to be explained or demonstrated. The clinical picture supports vascular involvement, but obvious limitations of inner ear study make this difficult to corroborate.

OBJECTIVES

To determine the role of thrombophilic genetic variants that may affect platelet function and to assess the cardiovascular risk profile in a cohort of patients with iSSNHL.

PATIENTS AND METHODS

118 Caucasian patients with iSSNHL were recruited from the same geographical area and enrolled prospectively in this study. Clinical data were obtained for each patient. Polymorphisms of the platelet glycoprotein subunit IIIa gene, ITGB3 (PLA1/A2, rs5918), and of the platelet glycoprotein subunit Ia gene, ITGA2 (C807T, rs1126643) were analyzed. A control group of 161 age- and gender-matched healthy individuals from the same geographical area was recruited for genetic comparisons. In order to determine the cardiovascular risk profile of each patient and of our cohort, a cross-sectional assessment was performed by means of a calibrated Framingham coronary heart disease risk scale. Risk factor proportions were compared to those recommended in European guidelines for coronary prevention, which are also based on the Framingham function.

RESULTS

A significantly high prevalence of the 807T allele of platelet glycoprotein subunit Ia was found in patients compared to controls. There was a significant correlation between the 807TT homozygous genotype and a low probability of recovery. The PLA1/A2 polymorphism of platelet glycoprotein subunit IIIa was not associated with recovery, with a similar genotype prevalence being found in patients and controls. In terms of cardiovascular risk profile, patients did not present an excess of baseline coronary risk factors compared to the general population in the same geographical area.

CONCLUSIONS

Patients with iSSNHL had a higher prevalence of the 807T thrombophilic polymorphism of platelet glycoprotein Ia/IIa. Patients homozygous for this polymorphism are less likely to recover from iSSNHL. Classical cardiovascular risk factors were not related to iSSNHL.

Genetic regulation of platelet receptor expression and function: application in clinical practice and drug development

Understanding genetic contributions to platelet function could have profound clinical ramifications for personalizing platelet-directed pharmacotherapy, by providing insight into the risks and possible benefits associated with specific genotypes. This article represents an integrated summary of presentations related to genetic regulation of platelet receptor expression and function given at the Fifth Annual Platelet Colloquium in January 2010. It is supplemented with additional highlights from the literature covering (1) approaches to determining and evidence for the associations of genetic variants with platelet hypo- and hyperresponsive phenotypes, (2) the ramifications of these polymorphisms with regard to clinical responses to antiplatelet therapies, and (3) the role of platelet function/genetic testing in guiding antiplatelet therapy.

Inherited Thrombophilia

Inherited thrombophilia can be defined as a genetically determined predisposition to the development of thromboembolic complications. Since the discovery of activated protein C resistance in 1993, several additional disorders have been described and, at present, it is possible to identify an inherited predisposition in about 60 to 70% of patients with such complications. These inherited prothrombotic risk factors include qualitative or quantitative defects of coagulation factor inhibitors, increased levels or function of coagulation factors, defects of the fibrinolytic system, altered platelet function, and hyperhomocysteinemia. In this review, the main inherited prothrombotic risk factors are analyzed from epidemiological, laboratory, clinical, and therapeutic points of view. Finally, we discuss the synergism between genetic and acquired prothrombotic risk factors in particular conditions such as childhood and pregnancy.

Genetic polymorphisms for the study of multifactorial stroke

Single-gene disorders explain only a minority of stroke cases. Stroke represents a complex trait, which is usually assumed to be polygenic. On this topic, the role of a wide number of candidate genes has been investigated in stroke through association studies, with controversial results. Therefore, it is difficult for the clinician to establish the validity and the level of clinical applicability of the previously reported associations between genetic factors and stroke. This review is an update and an extensive analysis of the more recent association studies conducted in stroke. We evaluated a number of studies on several candidate genes (including F5, F2, FGA/FGB/FGG, F7, F13A1, vWF, F12, SERPINE1, ITGB3/PLA1/PLA2/ITGA2B, ITGA2, GP1BA, ACE, AGT, NOS3, APOE, LPL, PON1, PDE4D, ALOX5AP, MTHFR, MTR, and CBS), providing a final panel of genes and molecular variants. We categorized this panel in relation to the degree of association with stroke, supported by the results of meta-analyses and case-control studies. Our findings could represent a useful tool to address further molecular investigations and to realize more detailed meta-analyses.

807C/T polymorphism in the platelet glycoprotein Ia gene in young patients with ischemic stroke of undetermined etiology

Platelet membrane glycoprotein receptors mediate key reactions in arterial thrombosis. The relationship between glycoprotein Ia polymorphisms and the risk of ischemic stroke, however, remains controversial. A matched case-control study was conducted to evaluate this question in young patients. Seventy patients with ischemic stroke of undetermined etiology, with ages ranging from 15 to 50 years, and 70 healthy control individuals, matched by age, gender and ethnicity, were tested for the 807C/T genotypes. Patients were excluded if they had systemic diseases known to predispose to thrombosis or any defined etiology of ischemic stroke. The frequencies of the 807T glycoprotein Ia variant and of conventional risk factors for arterial thrombosis (hypertension, smoking, diabetes mellitus, use of oral contraceptives, levels of serum cholesterol and body mass index) were compared in stroke patients and control individuals. The 807T allele was found in 61% of patients and 53% of control individuals (matched-pair odds ratio, 1.38; 95% confidence interval, 0.69-2.74; P = 0.42). Arterial hypertension and smoking were more frequent in patients than control individuals (matched-pair odds ratio, 2.83; 95% confidence interval, 1.05-8.02; P = 0.04; and odds ratio, 3.20; 95% confidence interval, 1.10-9.97, P = 0.03, respectively). In conclusion, our results do not support an independent association between the 807C/T polymorphism and stroke of undetermined etiology. The interplay of this polymorphism with arterial hypertension in the causation of ischemic stroke requires further evaluation.

Lack of association between the platelet glycoprotein Ia C807T gene polymorphism and coronary artery disease: a meta-analysis

BACKGROUND

The platelet-collagen receptor, glycoprotein (GP) la/lla plays a crucial role in the adhesion of platelets to fibrillar collagen, an event contributing to the pathogenesis of thrombosis. The C807T polymorphism of the GPla gene is considered a genetic marker of the platelet GPla/lla density. The importance of the GPla gene C807T polymorphism as a genetic risk factor for coronary artery disease (CAD) remains controversial. To assess this association, we performed a meta-analysis of published data.

METHODS

A comprehensive meta-analysis of 19 studies, with a total sample of 13835 subjects using random effects models.

RESULTS

The C versus T allele contrast gave an OR of 0.998 with 95% Cl 0.937-1.064. Similarly, comparing the C homozygotes with the T homozygotes, the CC genotype versus the others and the TT genotype versus the rest, no evidence of any gene-disease association was obtained. Furthermore, the meta-regression analysis did not disclose any variable that could modify the role of this polymorphism in the development of CAD.

CONCLUSION

Our findings support the view that C807T polymorphism of the GPla gene is not a significant risk factor for CAD, either alone or in combination with other major cardiovascular risk factors.

Genetic Polymorphisms of Platelet Glycoprotein Ia and the Risk for Premature Myocardial Infarction

OBJECTIVES

The aim of this research was to evaluate the effect of genetic polymorphisms C807T and G1648A of platelet glycoprotein Ia (GPIa), on the risk for myocardial infarction (MI) and on the release of soluble CD40 ligand (sCD40L) during the acute phase of MI and one year after the event.

BACKGROUND

C807T and G1648A polymorphisms affect the density of GPIa on platelet surface, but their effect on the risk for MI and the release of sCD40L is unknown.

METHODS

The study population consisted of 219 patients with premature MI and 389 controls. One year after the event, 67 patients and 232 controls were recalled for the follow-up study.

RESULTS

The risk for MI in 807TT was 2.296 (95% confidence interval [CI]: 1.187 to 4.440) p < 0.05 versus CC + CT, 2.269 (95% CI: 1.085 to 4.745) p < 0.05 versus CC, and 2.135 (95% CI: 1.080 to 4.219) p < 0.05 versus CT. During the acute phase of MI, sCD40L was higher in 807CT + TT compared with 807CC (p < 0.01), an effect persisting after one year (p < 0.01). The carriage of 807T allele was an independent predictor for sCD40L during the acute phase of MI (beta = 9.442 [standard error (SE): 2.526], p = 0.001) and in the same patients one year later (beta = 8.282 [SE: 2.044], p = 0.001). In healthy individuals, 807T allele was associated with higher sCD40L levels compared with 807CC (p < 0.05), only among those with von Willebrand factor greater than or equal to median.

CONCLUSIONS

Genetic polymorphism C807T increases the risk for premature MI. 807T allele is an independent predictor for sCD40L levels during the acute phase of premature MI as well as one year after the event, while it is associated with elevated sCD40L levels in healthy subjects, only in the presence of high von Willebrand levels.

Role of thrombophilic gene polymorphisms in branch retinal vein occlusion

OBJECTIVE

Branch retinal vein occlusion (BRVO) is a common cause of severe visual loss. Numerous risk factors, including arterial hypertension, diabetes mellitus, and arteriosclerosis, have been identified. Gene polymorphisms affecting hemostasis may also play a role in the pathogenesis of BRVO. The present study was therefore done to determine the prevalence of genetic polymorphisms in factors implicated in hypercoagulability among patients with BRVO.

DESIGN

Retrospective case-control study.

PARTICIPANTS

The study cohort consisted of 294 patients with BRVO and 294 control subjects, matched for age and gender.

METHODS

Determination of genotypes was done by allele-specific digestion of polymerase chain reaction products, or by 5' exonuclease assay (TaqMan).

MAIN OUTCOME PARAMETERS

Genotypes of factor V R506Q (factor V Leiden), prothrombin 20210G>A, fibrinogen beta -455G> A, factor XII (FXII) 46C>T, and ITGA2 807C>T (platelet glycoprotein Ia [GPIa] 807C>T) and ITGB3 L59P (platelet GPIIIa PlA1/PlA2) polymorphisms.

RESULTS

Genotype distributions of the investigated gene polymorphisms did not differ significantly between patients and control subjects. In contrast, significantly increased prevalences of arterial hypertension and hypercholesterolemia were found among patients with BRVO. In a logistic regression analysis, the presence of arterial hypertension was associated with an odds ratio (OR) of 2.32 (95% confidence interval [CI], 1.62-3.32), whereas hypercholesterolemia yielded an OR of 2.54 (95% CI, 1.74-3.70) for BRVO.

CONCLUSION

Our data indicate that the prevalences of the investigated gene polymorphisms do not differ significantly in patients with BRVO and control subjects. This suggests that these polymorphisms are not major risk factors for BRVO.

Association of the −92C/G and 807C/T Polymorphisms of the α2Subunit Gene With Human Platelets α2β1Receptor Density

OBJECTIVE

Platelet adhesion to the subendothelial tissue via the collagen receptor alpha2beta1 is a crucial event in vascular biology. Although evidence has been provided that the number of platelets alpha2beta1 copies is genetically determined, the molecular change primary responsible has not been yet elucidated. The aim of our present study was to investigate the effect of combined polymorphisms within both regulatory (-52C/T and -92C/G) and coding regions (807C/T and 1648A/G) of the alpha2 subunit gene on human platelets alpha2beta1 receptor density and/or susceptibility to coronary artery disease (CAD).

METHODS AND RESULTS

Among 254 cardiac surgery patients, no evidence was found for an association between the alpha2 subunit gene polymorphisms and CAD. In contrast, in a subgroup of 113 patients, we observed a significant association between all polymorphisms except -52C/T and alpha2beta1 receptor level. Furthermore, when 3 groups of patients were defined according to the tertiles of platelets alpha2beta1 copies, the -92C/807T haplotype was more frequent in the group of patients with high alpha2beta1 receptor level.

CONCLUSIONS

These results suggest that an individual effect of each polymorphism located either in the coding or promoter sequence of the alpha2 gene may act in combination to modulate variations in platelets alpha2beta1 receptor density.

Association of polymorphisms of platelet membrane integrins alpha IIb(beta)3 (HPA-1b/Pl) and alpha2(beta)1 (alpha807TT) with premature myocardial infarction

Conflicting results of an association of the human platelet antigen 1b (HPA-1b/PlA2), localized on the beta-subunit of the integrin alpha(IIb)beta3, and the alpha(2)807TT genotype of the integrin alpha2beta1 with coronary atherosclerosis and myocardial infarction have been reported. Both platelet receptor polymorphisms were genotyped in 3261 patients who had undergone coronary angiography, including 1175 survivors of a myocardial infarction, 1211 individuals with coronary artery disease but no history of myocardial infarction, and 571 control patients without angiographic coronary artery disease, and in 793 blood donors. In a case-control design, the prevalence of HPA-1b and alpha(2)807TT genotypes did not differ significantly between the patient groups with coronary artery disease or myocardial infarction and patient controls or blood donors. By contrast, using a multivariate case-only design, it was found that the median age of onset of myocardial infarction was 5.2 years earlier (P = 0.006) in carriers of the HPA-1b allele and 6.3 years earlier (P = 0.006) in carriers of the alpha(2)807TT genotype in the 264 survivors of myocardial infarction of recent onset with one- or two-vessel coronary artery disease. A significant interaction with the conventional risk factors hypercholesterolemia, smoking, diabetes, hypertension, and hyperfibrinogenemia was excluded. Human platelet antigen 1b and alpha(2)807TT are associated with premature myocardial infarction but not with coronary artery disease, suggesting a role of distinct integrin genotypes for increased platelet thrombogenicity. This association requires confirmation in follow-up studies.

Genetics of platelet glycoprotein receptors: risk of thrombotic events and pharmacogenetic implications

Platelet aggregation and coronary thrombosis have a central role in the development of acute coronary syndromes and myocardial infarction (MI). Therapies aimed at inhibiting platelet aggregation have shown great benefit in individuals with coronary disease or with multiple risk factors for coronary disease. Genetic variation in platelet surface receptors mediating thrombus formation has been suggested to be associated with platelet hyperreactivity, with increased risk of MI and possibly with the benefit received from various antithrombotic drug treatments. This review focuses on discrepancies and their likely explanations in studies on platelet glycoprotein genetics. Current knowledge on important issues concerning coronary event phenotypes and pharmacogenetics is analyzed. Possible future applicability of these data to patient treatment is also discussed.

807 C/T Polymorphism of the glycoprotein Ia gene and pharmacogenetic modulation of platelet response to dual antiplatelet treatment

Glycoprotein (GP) Ia/IIa is a major platelet-collagen receptor playing a key role in thrombosis following collagen exposure. The 807 C/T polymorphism of the GP Ia gene (ITGA2) has been associated with platelet GP Ia/IIa receptor expression, having T-allele carriers, increased receptor density and thrombotic risk. The aim of the study was to assess the role of the 807 C/T polymorphism on modulating platelet function in patients undergoing coronary stenting receiving a 300 mg clopidogrel loading dose. Platelet aggregation was assessed in 44 patients by light transmittance aggregometry following adenosine diphosphate and collagen stimuli at baseline, and 10 min, 4 h and 24 h after clopidogrel front loading. The T allele was found in 73% of patients. Clopidogrel reduced adenosine diphosphate-induced platelet aggregation (P < 0.01), which was similar in carriers and non-carriers of the T allele throughout the study (P = 0.73). Clopidogrel reduced collagen-induced platelet aggregation only in non-carriers of the T allele (P = 0.03), which resulted in an increase in T allele carriers during the overall study (P = 0.04). In conclusion, the T allele of the GP Ia gene modulates platelet aggregation and clopidogrel antiplatelet effects, suggesting an enhanced reactivity to fibrillar collagens (exposed during coronary stenting) in T allele carriers and might contribute to an increased thrombotic risk in these patients.

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.

The platelet glycoprotein Ia/IIa gene polymorphism C807T/G873A: a novel risk factor for retinal vein occlusion

Retinal vein occlusion (RVO) is associated with hyperhomocysteinaemia and the antiphospholipid syndrome-disorders known to contribute to both arterial and venous thrombosis. In both of these conditions and RVO, platelet activation occurs. Aspirin, not warfarin, is the most effective antithrombotic agent in RVO and, taken together, these observations suggest an important role for platelets in this common ocular thrombotic condition. Platelet glycoprotein Ia/IIa (GpIa/IIa) is an adhesion molecule mediating platelet-collagen interactions and is key to the initiation of thrombosis. Recently, the cellular density of this molecule was shown to be determined by two silent, linked polymorphisms (C807T/G873A) within the GpIa/IIa gene. There is evidence that some of the resulting genotypes are associated with thrombo-embolic disease. This study therefore aimed to establish the prevalence of the GpIa/IIa polymorphisms and the three commonest hereditary thrombophilic disorders (prothrombin gene G20210A (PT) mutation, Factor V Leiden (FVL), and the thermolabile methylene tetrahydrofolate reductase C677T (MTHFR) mutation) in patients with RVO and normal controls. The GpIa/IIa polymorphisms and thrombophilic abnormalities were all identified using the polymerase chain reaction.Our results show that the frequency of the GpIa/IIa polymorphisms was similar in our normal control population to previously published series. Patients with RVO, however, had only a 10% (4/40) frequency of the lowest risk subtype (CC/GG) compared to 37.5% (15/40) in the control group-P 0.0039. The incidence of the PT, FVL, and MTHFR thrombophilic mutations was not different between the two groups, but interestingly none of the 7/40 RVO cases with a PT, FVL, or MTHFR mutation had the low-risk GpIa/IIa genotype while all but one of the controls did-P<0.05. Thus, 17.5% of RVO patients harboured more than one prothrombotic abnormality. The principal difference between the RVO and control group was the very high incidence of the intermediate-risk GpIa/IIa subtype (CT/GA)-82.5 vs 50%, P&<0.05. These results suggest a major role for GpIa/IIa polymorphisms in the pathogenesis of RVO.

The role of platelet receptors and adhesion molecules in coronary artery disease

Platelets play a significant role in coronary artery disease through interactions with each other and with other cell types. These interactions are mediated by certain receptors on the surface of platelets and other cells which can lead to intra-coronary thrombus formation and occlusion that may result in acute coronary syndromes. The important roles of the currently available anti-platelet therapies have been well established in many clinical outcome trials in cardiovascular patients. An understanding of these different interactions provides the clinician with a background that supports the clinical importance of currently available anti-platelet therapies. Moreover, knowledge of the mechanisms of cellular crosstalk will lead to important advances in the development of better antithrombotic therapies.

Increased platelet-collagen interaction associated with double homozygosity for receptor polymorphisms of platelet GPIa and GPIIIa

OBJECTIVE

There is considerable controversy regarding the clinical role of the single-nucleotide polymorphisms (SNPs) of the platelet glycoprotein receptor GPIa C807T and the Pl(A1/A2) of GPIIIa as cardiovascular risk factors. We hypothesized that two combined SNPs in their homozygous prothrombotic forms could clarify their pathophysiological impact.

METHODS AND RESULTS

We identified a family with a striking history of premature cardiovascular events and a high frequency of the prothrombotic form of the two SNPs. From this family, the platelets of a healthy, 27-year-old propositus with this double homozygosity were compared with three matched male neutral gene variant controls. The propositus had shortened PFA-100 closure times and an increased platelet aggregation response to collagen. Platelet deposition to collagen was augmented under the blood flow conditions of a high shear rate model (1600 s(-1)). Platelet adhesion on collagen monomers was induced in a static system, leading to the promotion of subsequent procoagulant activity.

CONCLUSIONS

The combined homozygous prothrombotic SNPs of GPIa and GPIIIa are associated with an increased platelet-collagen interaction and procoagulant activity that can be readily demonstrated in several independent systems. Our patient may serve as a useful model for the functional consequences of two combined, potentially procoagulant, platelet SNPs.

Platelet collagen receptor GPIa (C807T/HPA-5) haplotype is not associated with an increased risk of fatal coronary events in middle-aged men

Platelet GPIa/IIa receptors play key roles in the adhesion of platelets to collagen during the formation of coronary thrombosis. The C807T and HPA-5 polymorphisms of the gene for GPIa define three distinct alleles of GPIa which are associated with the surface expression of the protein in an allele-dependent fashion. Significance of these polymorphisms in victims of sudden cardiac death (SCD) was studied in Helsinki Sudden Death Study (HSDS) comprising 700 autopsied middle-aged Caucasian Finnish men with 288 SCD victims and 84 men with fatal acute myocardial infarction (AMI). The high-expression A1 allele was found in 36.6% of control men as opposed to 38.0% of all SCD victims and 36.9% of men with fatal AMI (P>0.4). The high-expression A1A1 genotype was found in 11.9% of men with fatal AMI and 10.0% of controls as opposed to the low-expression A2A2 genotype which was found in 29.8% of men with fatal AMI and in 31.2% of controls (OR 1.2, P>0.3). Age group (under/over 55) had no effect on the results. Our results do not support an effect of the GPIa haplotype on fatal coronary events among middle-aged men.

Polymorphisms of genes affecting thrombosis and risk of myocardial infarction

BACKGROUND

As thrombosis is an essential factor in the pathogenesis of acute myocardial infarction (AMI), the genes of proteins affecting haemostasis are good candidate genes for AMI.

DESIGN

Associations of the known polymorphisms of the coagulation factor VII (FVII) gene (R353Q), the coagulation factor XIII (FXIII) gene (V34L) and the glycoprotein Ia (Gp1a) gene (C807T) with the occurrence of AMI were studied in 142 AMI survivors and 142 age- and sex-matched control subjects.

RESULTS

Among those who smoked, the L34 allele of the amino acid FXIII polymorphism was less common in the AMI patients (16%) than in the controls (27%) (P = 0.06), suggesting a possible interaction of AMI risk between the FXIII genotype and smoking status. No differences in the allele or genotype frequencies of the studied polymorphisms were seen between the whole study groups. Logistic regression analysis showed the carriers of the L34 allele of the FXIII amino acid polymorphism to have a significantly (P = 0.03) lower AMI risk compared with those homozygous for the V34 allele (odds ratio = 0.54, 95% confidence interval 0.31-0.93).

CONCLUSION

The L34 allele of the amino acid polymorphism of the FXIII gene is associated with a decreased risk of AMI, and this protecting association seems to be more pronounced in smokers.

Genetic polymorphisms associated with venous and arterial thrombosis: an overview

OBJECTIVE

To provide an overview of genetic polymorphisms associated with thrombotic cardiovascular disease.

DATA SOURCES

A literature search using the National Library of Medicine database.

STUDY SELECTION

The literature on genetic polymorphisms associated with venous and arterial thrombosis was reviewed.

DATA EXTRACTION

Based on the literature review, the clinical significance of polymorphisms in various coagulation proteins was assessed and a summary was developed.

CONCLUSIONS

Thrombosis is a multifactorial disorder, with both congenital and acquired risk factors. It is now clear that there are many genetic abnormalities that impart an increased risk for thrombophilia, and the presence of more than 1 abnormality results in a further increased risk of thrombosis. In hemostasis, there is a balance between procoagulant factors and natural anticoagulant proteins. The first genetic thrombotic disorders described were deficiencies of the natural anticoagulants, such as antithrombin, protein C, and protein S, but these abnormalities are rare and are caused by many different mutations. More recently, single polymorphisms that are relatively common in the general population have been described in procoagulant factors, such as factor V and prothrombin, which impart an increased risk for venous thrombosis. As more scrutiny is placed on the hemostatic system, further polymorphisms have come to light. The current challenge is to elucidate the relationship between these new polymorphisms and either venous or arterial thrombotic cardiovascular disease.

Influence of platelet collagen receptor polymorphisms on risk for arterial thrombosis

CONTEXT

Collagens are major components of the vascular subendothelium, and the interaction of platelets with collagens initiates normal hemostasis or pathologic arteriothrombosis. Genetic factors that affect the interaction of platelets with collagens could represent risk factors for either arteriothrombosis or excessive hemorrhage. In this regard, we first found that platelet levels of one of the major platelet collagen receptors, integrin alpha(2)beta(1), vary up to 10-fold in normal healthy individuals and that the higher-level phenotype is associated with allele 1 (807T) of the integrin alpha(2) gene. More recently, we found that there is roughly a fivefold range in platelet glycoprotein VI content among normal individuals, which may also influence risk for thromboembolism.

OBJECTIVE

To determine if genetic polymorphisms of platelet glycoproteins involved in collagen-related function are associated with higher risk for thrombotic disorders, such as coronary heart disease, myocardial infarction, or stroke.

METHODS

We examined the genetic mechanisms responsible for variation in expression levels of the collagen receptor integrin alpha(2)beta(1) and the potential influence of this variation on risk for thrombotic diseases.

RESULTS

We found that patients with arteriothrombotic diseases have a higher frequency of alpha(2) allele 1 (associated with higher levels of platelet integrin alpha(2)beta(1)). We further found that platelet glycoprotein VI content directly correlates with platelet prothrombinase activity, suggesting that a higher phenotype of platelet glycoprotein VI also may contribute to increased risk of arteriothrombotic diseases.

CONCLUSION

Genetic polymorphisms that influence the level or function of platelet collagen receptors need to be seriously considered as genetic risk factors for arteriothrombotic diseases.

A novel gain-of-function mutation of the integrin alpha2 VWFA domain

Integrin alpha2beta1 is the major receptor for collagens in human tissues, being involved in cell adhesion and the control of collagen and collagenase gene expression. The collagen binding site of alpha2beta1 has been localized to the alpha2 von Willebrand Factor type A (VWFA) domain (A-domain or I-domain) and the residues responsible for the interaction with collagen have been mapped. We report a study of alpha2 VWFA domain in which residue E318, which lies outside the collagen binding site, is mutated to tryptophan, showing that this is a gain-of-function mutation. Recombinant alpha2-E318W VWFA domain showed elevated and specific binding to collagen I compared with the wild-type. Side chain hydrophobicity was important for the gain-of-function as elevated binding was seen with E318I and E318Y, but not with E318R. The E318W mutation had additional effects on VWFA domain properties as alpha2-E318W VWFA domain differed from the wild-type in its cation preferences for ligand binding and in binding to monoclonal antibody JA203, which bound at a site distal to E318. The gain-of-function effect was not restricted to binding to collagen I as alpha2-E318W also showed elevated binding to collagen IV, collagen I C-propeptide, laminin and E-cadherin. Binding to these ligands was inhibited by collagen peptide containing the GFOGER motif, indicating that these bound to the VWFA domain by a similar mechanism to collagen I. These data indicate that residue E318 plays a novel and important role in modulating alpha2 VWFA domain--ligand binding and may be involved in the conformational changes associated with its regulation.

The influence of platelet collagen receptor polymorphisms in hemostasis and thrombotic disease

Extracellular collagens modulate the rate of platelet activation and thereby markedly influence hemostasis and thrombosis. Platelet receptors for collagens, such as the integrin alpha(2)beta(1), platelet glycoprotein (GP) VI or, indirectly, the GPIb complex, are unexploited targets of pharmacological control, and polymorphisms of these receptors have recently become factored into the genetic risk for thrombosis. Seemingly contradictory findings already exist with regard to the contribution of GPIbalpha and integrin alpha(2) polymorphisms, but these discrepancies will be resolved once there is better standardization of clinical studies. There is already substantial evidence that GPIbalpha VNTR A or B alleles, the GPIbalpha-5C allele, and integrin alpha(2) allele 1 (T(807)) each contribute to increased risk for morbidity in thrombotic disease. However, larger, prospective genetic and epidemiological studies are needed to clarify the role of each of these polymorphisms, the contribution of other platelet receptor polymorphisms, and the synergistic effects of combinations of these factors. In addition, in vitro studies that establish the functional relevance of these polymorphisms will provide sound biological explanations for the results of clinical correlation studies.

Platelet glycoprotein Ia 807C/T (Phe224) and 873G/A (Thr246) dimorphisms in Turkey

At sites of vascular injury, the platelet collagen receptor Glycoprotein Ia/IIa (GPIa/IIa) acts as an important mediator of platelet adhesion to fibrillar collagens. Two silent polymorphisms (807C/T and 873G/A) within the glycoprotein Ia gene have been implicated in increased risk of developing thrombosis and myocardial infarction in affected individuals. To provide basis for future studies, we examined the frequency of these GPIa polymorphisms for people in Turkey. We analyzed 118 unrelated individuals for their genotypes of the GPIa gene using a multiplexed allele specific-PCR based method. The allelic frequencies were found to be 34% for 807T/873A and 66% for 807C/873G; the genotypic frequencies were 13% for 807TT/873AA, 44% for 807CT/873GA, and 43% for 807CC/873GG.

Novel platelet membrane glycoprotein VI dimorphism is a risk factor for myocardial infarction

BACKGROUND

Glycoprotein (GP) VI plays a crucial role in platelet activation and aggregation. We investigated whether polymorphic variation at the GP VI locus confers an increased risk of myocardial infarction (MI).

METHODS AND RESULTS

Coding and 5' and 3' non-coding regions of the GP VI gene were analyzed by polymerase chain reaction and conformation sensitive gel electrophoresis in 21 healthy subjects. Ten dimorphisms, 5 of which predicted amino acid substitutions (T13254C, A19871G, A21908G, A22630T, C22644A), were identified. Two core haplotypes involving 7 dimorphisms (C10781A and G10873A and all those predicting amino acid substitutions) were apparent. The contribution of the T13254C dimorphism, which predicted the substitution of serine 219 by proline, to risk of MI was assessed in 525 patients with acute MI and 474 controls, all aged <75 years. The allelic odds ratio (OR) for MI associated with the 13254C allele was 1.16 (95% CI, 0.91 to 1.46; P=0.23). Compared with corresponding control subgroups, the 13254CC genotype was more common among cases who were female (OR, 4.52; 95% CI, 1.23 to 16.64; P=0.029), nonsmokers (OR, 2.50; 95% CI, 0.98 to 6.38; P=0.048), aged >/=60 years (OR, 6.48; 95% CI, 1.47 to 28.45; P=0.009) or carried the beta-fibrinogen -148T allele associated with increased fibrinogen levels (OR, 10.49; 95% CI, 1.32 to 83.42; P=0.02). In logistic regression analysis that took other cardiovascular risk factors into account, the interactions of GP VI genotype with age (P=0.005) and beta-fibrinogen genotype (P=0.035) remained significant.

CONCLUSIONS

The GP VI 13254CC genotype increases the risk of MI, particularly in older individuals, and the interaction of the GP VI 13254C allele with other candidate risk alleles may accentuate this risk.

The role of platelet collagen receptor (glycoprotein Ia/IIa; integrin alpha2 beta1) polymorphisms in thrombotic disease

Differences in rates of platelet activation induced by extracellular matrix components such as collagens markedly influence normal hemostasis and the pathologic outcome of thrombosis. Thus, platelet collagen receptors, the integrin alpha2beta1, glycoprotein VI, and the glycoprotein Ib complex, represent unexploited targets of pharmacologic control. Polymorphisms of these receptors are now understood as factors that potentially contribute to thrombotic risk. There is substantial evidence that the GPIbalpha variable number of tandem repeats A or B alleles, the -5C allele of GPIbalpha, and the integrin alpha2 allele 1 (T807) each contribute to risk for and morbidity from thrombotic disease. The extent of their individual contributions is disputed. More well-designed, large, prospective, genetic and epidemiologic studies are needed to clarify the role of these and other platelet receptor polymorphisms, and additional in vitro studies are needed to provide a sound biologic explanation for the outcomes of clinical correlations.

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.

The C807T/G873A polymorphism in the platelet glycoprotein Ia gene and the risk of acute coronary syndrome in the Italian population

Membrane glycoprotein (GP) Ia/IIa mediates platelet adhesion to collagen. The linked C807T/G873A polymorphisms in the GP Ia gene are correlated with a variable expression of the platelet surface receptor, the 807 TT/873 AA genotype being associated with a higher receptor density. Our study aimed to evaluate the possible role of the GP Ia C807T/G873A polymorphism as a risk factor for acute coronary syndrome in the Italian population. We investigated 157 patients with acute coronary syndrome (117 with myocardial infarction and 40 with severe unstable angina) as the first manifestation of coronary disease occurring before 65 years of age, compared with 312 healthy controls. All individuals were of Italian ancestry and were genotyped for the GP Ia C807T/G873A polymorphism. Complete linkage between the 807 and 873 sites was found in all samples. The 807 TT genotype was present in 12.7% of cases and in 4.8% of controls; the odds ratio for acute coronary syndrome was 2.9 (95% CI 1.4--5.8) for the 807 TT genotype compared with C-allele carriers and 0.6 (95% CI 0.4--0.9) for the 807 CC genotype compared with T-allele carriers. For the TT genotype, compared with CC homozygotes, the increase in risk was 3.4-fold in patients with at least one risk factor (smoking, hypercholesterolaemia, diabetes, systemic hypertension) and 4.1-fold in patients with angiographically diagnosed two- or three-vessel disease. We conclude that the GP Ia 807 TT (873 AA) genotype is associated with an increased risk of acute coronary syndrome in the Italian population; conversely, the GP Ia 807 CC (873 GG) genotype seems to represent a protective factor.

Glycoprotein Ia C807T polymorphism and risk of restenosis following coronary stenting

Platelets are thought to contribute to development of restenosis following percutaneous coronary interventions. The glycoprotein Ia/IIa complex is a major platelet collagen receptor, its surface expression being influenced by two, linked single nucleotide polymorphisms (C807T and G873A) in the glycoprotein Ia gene. T807 is associated with increased expression of this integrin receptor. We assessed whether T807 is associated with an increased risk of restenosis in 1769 consecutive patients treated with coronary stenting. 6-month follow-up angiograms were available in 82.4% of the patients. C807T genotype distribution was CC in 35.8%, CT in 47.6% and TT in 16.6% of the patients. Restenosis (diameter stenosis > or =50% at follow-up angiography) occurred in 32.9% of CC, 31.5% of CT and 32.1% of TT patients (P=0.87). The rate of major adverse cardiac events (death, myocardial infarction or need of reintervention) within 1 yr was 21.6% for CC, 21.7% for CT and 21.2% for TT patients (P=0.98). Thus, carriage of the GP Ia T807 allele is not associated with an increased risk of restenosis or unfavorable late outcome following coronary artery stenting.

Platelet polymorphisms in thrombotic disorders

Plaque rupture and/or endothelial damage lead to exposure of von Willebrand factor (VWF) and collagen which facilitate the adhesion of circulating platelets via glycoprotein (GP) GPIb-IX-V and integrin alpha2 beta1, respectively, to the damaged vessel wall. This process activates the platelets and leads to a conformational change of a second integrin alphaIIb beta3 that facilitates fibrinogen binding and platelet aggregation. Thrombin generated at the blood-plaque interface converts fibrinogen to fibrin, which stabilizes thrombus growth. Therefore, any genetic differences that might alter surface expression or activity of these receptors could influence the risk for adverse outcome as a result of the hemostatic process. In the last five years, there has been a rapid accumulation of literature concerning the relationship between genetic variations in platelet glycoproteins and risk for coronary heart disease. In this study, we have presented a comprehensive review of the impact of platelet receptor polymorphisms and thrombotic risk.

Genetics of arterial prothrombotic risk states

Coronary artery disease is a leading cause of death worldwide and the largest killer of men and women in the United States. The pathophysiology of myocardial infarction is multifactorial, and numerous physiologic systems converge to dictate the formation of the two fundamental lesions, thrombosis and atherosclerosis. In this review we address genetic aspects of arterial thrombosis and the key thrombotic factors that have been associated with the increased risk for its development. Specifically, we consider components of coagulation, fibrinolysis, and platelet adhesive receptors, and we review the genetic epidemiology and in vitro laboratory data regarding their risk for the acute coronary syndromes. In combination with traditional risk factor assessment, in the near future these inherited markers can be used to manage patients with vascular disease through a better utilization of invasive or expensive diagnostic testing, as well as pharmacologic intervention.

Thrombophilia, polymorphisms, and vascular disease

Thrombophilia traditionally refers to rare inherited defects leading to enhanced coagulation, especially of the venous system. In recent years, a broader search for genetic polymorphisms of prothrombotic genes has been carried out to determine the relative impact on venous and arterial thrombosis. The bulk of evidence is drawn from numerous, often small, heterogeneous, case control association studies, with a variety of end points (deep venous thrombosis, myocardial infarction, or stroke). The data are often conflicting and inconclusive with only factor V Leiden and prothrombin polymorphisms having clear associations with venous thrombosis. Many of the polymorphisms interact with established cardiovascular risk factors, in particular smoking, to increase greatly the risk of a thrombotic episode. Future studies will need to consider the confounding factors of sample size, race, and clinical end points as well gene-environment interactions.

Platelet glycoprotein polymorphisms as risk factors for thrombosis

Both blood platelets and genetics contribute to the development of acute ischemic arterial diseases. A careful analysis of the various clinical association studies supports a modest increased risk for coronary artery disease events in carriers of the PIA2 polymorphism of GPIIIa. Investigations with both platelets and stable cells lines have shown the PIA2 polymorphism is prothrombotic. Only a handful of studies have been performed for platelet GPla (integrin alpha2) and GPIb-IX-V, but there is support for the 807 T/C polymorphism of GPIa and the met145 and VNTR B/C genotype of GPIbalpha as risk factors in younger age groups. And isolated reports suggest other platelet polymorphisms (GPIIb, FcgammaRIIa, P-selectin, alpha2 adrenergic receptor, transforming growth factor [TGF]beta) are risk factors for arterial disease or produce a prothrombotic phenotype. Platelet glycoprotein polymorphisms should be added to the list of genetic risk factors for arterial thrombosis, particularly in younger patients and women.

Glycoprotein Ia gene C807T polymorphism and risk for major adverse cardiac events within the first 30 days after coronary artery stenting

The glycoprotein complex Ia/IIa (GP Ia/IIa) is a major collagen receptor on platelets and other cell types. Recently, linked polymorphisms within the coding region of the GP Ia gene (C807T and G873A) were identified that are related to GP Ia/IIa surface expression. The T807/A873 allele is associated with high expression, whereas the C807/G873 allele is associated with low surface expression of GP Ia/IIa. Subsequently, the T807 allele was found to be associated with coronary and cerebral infarction in younger patients. Platelet adhesion to the vessel wall plays a pivotal role in thrombosis after coronary artery stent placement. The goal of this study was to test whether C807T polymorphism is associated with a higher incidence of thrombotic events following coronary stenting. Consecutive patients treated with coronary stent placement (n = 1797) were genotyped for C807T polymorphism with polymerase chain reaction and allele-specific fluorogenic probes. The composite end point was defined as death, myocardial infarction, or urgent target vessel revascularization within 30 days of stent implantation. The genotype distribution of the study population was CC in 36.5%, CT in 46.7%, and TT in 16.8% of the patients. The incidence of the composite end point was 6.5% in T allele carriers and 5.3% in noncarriers (odds ratio for T allele carriage 1.23 [95% confidence interval, 0.81-1.86],P = .33). After adjusting for other baseline characteristics, the odds ratio for the composite end point was 1.15 (0.76-1.75). Therefore, C807T genotype has no significant influence on the major adverse events occurring after coronary artery stenting.

Glycoprotein Ia gene C807T polymorphism and risk for major adverse cardiac events within the first 30 days after coronary artery stenting

The glycoprotein complex Ia/IIa (GP Ia/IIa) is a major collagen receptor on platelets and other cell types. Recently, linked polymorphisms within the coding region of the GP Ia gene (C807T and G873A) were identified that are related to GP Ia/IIa surface expression. The T807/A873 allele is associated with high expression, whereas the C807/G873 allele is associated with low surface expression of GP Ia/IIa. Subsequently, the T807 allele was found to be associated with coronary and cerebral infarction in younger patients. Platelet adhesion to the vessel wall plays a pivotal role in thrombosis after coronary artery stent placement. The goal of this study was to test whether C807T polymorphism is associated with a higher incidence of thrombotic events following coronary stenting. Consecutive patients treated with coronary stent placement (n = 1797) were genotyped for C807T polymorphism with polymerase chain reaction and allele-specific fluorogenic probes. The composite end point was defined as death, myocardial infarction, or urgent target vessel revascularization within 30 days of stent implantation. The genotype distribution of the study population was CC in 36.5%, CT in 46.7%, and TT in 16.8% of the patients. The incidence of the composite end point was 6.5% in T allele carriers and 5.3% in noncarriers (odds ratio for T allele carriage 1.23 [95% confidence interval, 0.81-1.86],P = .33). After adjusting for other baseline characteristics, the odds ratio for the composite end point was 1.15 (0.76-1.75). Therefore, C807T genotype has no significant influence on the major adverse events occurring after coronary artery stenting.

Platelet glycoprotein Ia gene dimorphism alpha2-807 in malignant arrhythmia in coronary artery disease

It has been shown recently that the variable expression of the platelet collagen receptor integrin alpha2beta1 predisposes to thrombotic risk on the one hand and hemorrhagic risk on the other hand. The level of expression of the integrin alpha2beta1 is genetically controlled and associated with the alpha2-807 dimorphism. The expression level of this platelet collagen receptor may play a central role in the rapidly evolving coronary artery lesions that lead to malignant arrhythmia and sudden cardiac death. We studied allelic frequencies of the alpha2-807 dimorphism for their relation as a risk factor for malignant arrhythmia in a well-defined subgroup of patients with coronary artery disease. We compared allelic frequencies (by sequence specific primer polymerase chain reaction) of the dimorphism that is associated with integrin alpha2beta1 levels in 94 Caucasoid survivors of sudden cardiac death with a matched group of 106 patients with coronary artery disease without sudden cardiac death. Gene frequencies in the patient groups did not differ and were similar to those in the general population represented by 217 healthy individuals. There was no overrepresentation of an allele in any group. The inherited dimorphism that is associated with the levels of platelet integrin alpha2beta1 is not associated with malignant arrhythmia in coronary artery disease patients.