Analysis of Platelet Glycoprotein Ia (α2 Integrin) Allele Frequencies in Three North American Populations Reveals Genetic Association between Nucleotide 807C/T and Amino Acid 505 Glu/Lys (HPA-5) Dimorphisms

Association of the human platelet antigens polymorphisms with platelet count in patients with COVID-19

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), HPA-5 (GPIa/IIa), & HPA-15 (CD109) was investigated in 86 COVID-19-infected patients with thrombocytopenia (Group A) and 136 COVID-19-infected patients without thrombocytopenia (Group B). HPA genotyping was done by the sequence-specific primers PCR method. Lower HPA-3a and higher HPA-3b (P = 0.028) allele frequencies were seen in Group A than in Group B, and homozygosity for HPA 3b (P = 0.038) alleles was more prevalent in Group A than in Group B. The allele and genotype distributions of the other HPA polymorphic variants were similar between the two groups. Univariate analysis identified the CCGGGC (P = 0.016) combined genotype to be negatively associated & the TCGGGC (P = 0.003) and CCGGGC (P = 0.003) to be positively associated with thrombocytopenia. The frequency of anti-HPA-1a and anti-HPA-3a antibodies was significantly higher in all patients compared to other anti-HPAs antibodies (P < 0.05). These results highlight the role of HPAs in the thrombocytopenia of COVID-19 infected patients. This is the first evidence demonstrating the differential association of the six common HPA gene variants and specific HPA genotype combinations with thrombocytopenia in COVID-19-infected patients.

Enzymes that hydrolyze adenine nucleotides in platelets and polymorphisms in the alpha2 gene of integrin alpha2beta1 in patients with von Willebrand disease

Von Willebrand disease (VWD) is one of the most common inherited bleeding diseases caused by a qualitative or quantitative deficiency of the von Willebrand factor (FvW). FvW is a multimeric glycoprotein synthesized by megakaryocytes and endothelial cells and it is present in the subendothelial matrix, blood plasma, platelets, and endothelium. This glycoprotein plays an important role in thrombus formation by initiating platelet adhesion to sites of injury as well as platelet aggregation. The aim of this study was to evaluate the activities of enzymes that hydrolyze adenine nucleotides in platelets, ristocetin-induced platelet aggregation (RIPA), and polymorphisms of the alpha2 gene of alpha2beta1 integrin from VWD patients. Platelet nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase, and ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activities were verified in 14 VWD patients. For RIPA determination, a final concentration of 1.25 mg/ml of ristocetin was used. Polymorphisms of the alpha2 gene were analyzed through PCR. Platelet NTPDase and E-NPP were decreased in VWD patients. 5'-Nucleotidase activity was not statistically significant between controls and VWD patients. RIPA was significantly reduced, with an allelic frequency of 78.57% for 807C in VWD patients. Our results indicated reduced platelet NTPDase and E-NPP activities which might be related to the low platelet adhesiveness. The prevalence of the 807C allele might account for the variability in bleeding in VWD.

Polymorphisms of the human platelet alloantigens HPA-1, HPA-2, HPA-3, and HPA-4 in ischemic stroke

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), and HPA-5 (GPIa/IIa) was investigated in 329 stroke patients and 444 matched control subjects. HPA genotyping was done by PCR-SSP method. Lower HPA-1a (P < 0.001) and higher HPA-1b (P < 0.001) allele frequencies were seen in patients than control subjects, and homozygosity for HPA-1b (P < 0.001) alleles was more prevalent in stroke cases than in controls. The allele and genotype distributions of the other HPA polymorphic variants were similar between cases and controls. Select HPA combined genotypes comprising the 2121 (Pc = 0.008) and 2221 (Pc = 0.018) genotypes, which were positively associated, and the 1111 (Pc < 0.001), which was negatively associated with stroke, thereby conferred a disease susceptibility and protective nature to these genotype combinations. Multivariate analysis confirmed the negative association of the 1111 (P < 0.001) and the positive association of the 2121 (P = 0.017) combined genotypes with stroke, after adjustment for a number of covariates. This is the first evidence demonstrating differential association of the common 4 HPA gene variants and specific HPA genotype combinations with stroke.

The BC genotype of the VNTR polymorphism of platelet glycoprotein Ibalpha is overrepresented in patients with recurrent stroke regardless of aspirin therapy

BACKGROUND

The contribution of genetic factors to aspirin treatment failure (ATF) for secondary prevention is not settled in patients with ischemic stroke.

METHODS

We assessed the polymorphisms VNTR (A, B, C, D) of glycoprotein (GP) Ibalpha, 807C/T of GP Ia/IIa, and Pl(A1/A2) of GP IIb/IIIa, and the 5-year incidence of major recurrent events in 82 stroke patients with no major sources of cardioembolism (mean age 70, SD 9.0 years; female gender 23%). Using a structured interview, all participants confirmed good compliance with aspirin (100-300 mg/day) for secondary prevention. Demographics and atherothrombotic risk factors assessed included diabetes, hypertension, dyslipemia, smoking, and coronary heart disease.

RESULTS

Thirty-one stroke patients had one recurrent stroke or myocardial infarction within 33 (7-48) months of aspirin onset, while 51 patients demonstrated an uneventful clinical course. Female gender (p < 0.05), diabetes (p < 0.05), dyslipemia (p < 0.05), and the BC genotype of VNTR (25.8 vs. 7.8%, p < 0.05) were more prevalent in patients in whom aspirin failed to prevent clinical events than in those in whom it did not. The BC genotype of VNTR was the only factor that remained associated with ATF in an age-, sex-, and risk factor-adjusted logistic regression analysis (OR 9.6, 95% CI 1.5-61.0).

CONCLUSION

The BC genotype of the VNTR polymorphism of GP Ibalpha is an independent predictor of recurrent events in stroke patients treated with aspirin. This finding suggests that high shear-induced platelet activation mediated by GP Ibalpha and von Willebrand factor is an important contributor to ATF in the stroke population.

Role of glycoprotein Ia gene polymorphisms in determining platelet function in myocardial infarction patients undergoing percutaneous coronary intervention on dual antiplatelet treatment

Response variability to antiplatelet treatment has been described and the widespread use of acetylsalicylic acid (ASA) and clopidogrel requires clarification of the residual platelet reactivity (RPR). Various glycoprotein Ia (GpIa) polymorphisms have been investigated, but their influence on platelet reactivity in myocardial infarction (MI) patients undergoing percutaneous coronary intervention (PCI) on dual antiplatelet treatment is not still elucidated. Aim of this study was to evaluate the effect of C807T, G873A and T837C polymorphisms of GpIa on modulating platelet function in MI patients on dual antiplatelet treatment undergoing PCI. We measured platelet function by both a point-of-care assay (PFA100) and platelet-rich-plasma aggregation in 289 MI patients undergoing PCI and receiving dual antiplatelet treatment. Our data show that C807T/G873A polymorphisms, but not T837C, are associated with higher platelet reactivity. Carriers of the 807T/873A allele had significantly higher platelet aggregation values after arachidonic acid (AA) and collagen stimuli and, even if they did not reach the statistical significance, after 2 and 10 microM ADP stimuli; 807T/873A allele carriers had also significantly shorter closure times on PFA100/epinephrine membranes. At the multiple analyses, C807T/G873A polymorphisms resulted an independent risk factor for RPR defined by both AA induced platelet aggregation (OR=3.0, 95%CI 1.17-7.89, p=0.022) or by PFA100/epinephrine (OR=4.1, 95%CI 1.53-10.89, p=0.005). In conclusion, this study shows the 807T/873A allele of the GpIa gene is an independent risk factor for the RPR on dual antiplatelet treatment, and extends, in a larger acute coronary syndrome population, the observation that the 807T/873A allele is associated with higher platelet reactivity.

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.

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.

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.

Polymorphism of the human platelet antigen-5 system is a risk factor for occlusive vascular complications in patients with sickle cell anemia

BACKGROUND

Polymorphisms of platelet membrane glycoproteins such as human platelet antigen (HPA)-1b, HPA-2b, the -5T/C Kozak sequence and C807T have been described as risk factors for vascular disease. Vaso-occlusion episodes are a common feature of sickle cell anaemia (SCA), leading to complications such as stroke, acute chest syndrome, avascular head femur necrosis and priapism. Complex interactions are involved in vaso-occlusion, and activated platelets may play an important role. These data raised the question of whether platelet polymorphisms could be implicated in occlusive vascular complications (OVC) of SCA.

MATERIALS AND METHODS

In this study, 97 patients with SCA were analysed in two groups: 34 patients presenting with OVC (SCA-VC) and 63 without these complications (SCA-N). The distribution of the HPA-1, -2 and -5 systems, as well as C807T dimorphism and -5T/C Kozak sequence alleles, was evaluated using DNA-based methods.

RESULTS

Patients of the SCA-VC group showed a higher frequency of the HPA-5b allele (0.324) compared with those of the SCA-N group (0.111) (chi2 = 13.19, P = 0.0002). None of the other polymorphisms, isolated or associated as haplotypes, demonstrated any correlation with the development of OVC in these patients.

CONCLUSIONS

The findings of this study suggest that the HPA-5b allele is a genetic risk factor for the development of OVC in patients with SCA. This allele could be explored as a target for the development of new therapeutic approaches.

Collagen platelet receptor polymorphisms integrin alpha2beta1 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.

No evidence of association between prothrombotic gene polymorphisms and the development of acute myocardial infarction at a young age

BACKGROUND

We investigated the association between 9 polymorphisms of genes encoding hemostasis factors and myocardial infarction in a large sample of young patients chosen because they have less coronary atherosclerosis than older patients, and thus their disease is more likely to be related to a genetic predisposition to a prothrombotic state.

METHODS AND RESULTS

This nationwide case-control study involved 1210 patients who had survived a first myocardial infarction at an age of <45 years who underwent coronary arteriography in 125 coronary care units and 1210 healthy subjects matched for age, sex, and geographical origin. None of the 9 polymorphisms of genes encoding proteins involved in coagulation (G-455A beta-fibrinogen: OR, 1.0; CI, 0.8 to 1.2; G1691A factor V: OR, 1.1; CI, 0.6 to 2.1; G20210A factor II: OR, 1.0; CI, 0.5 to 1.9; and G10976A factor VII: OR, 1.0; CI, 0.8 to 1.3), platelet function (C807T glycoprotein Ia: OR, 1.1; CI, 0.9 to 1.3; and C1565T glycoprotein IIIa: OR, 0.9; CI, 0.8 to 1.2), fibrinolysis (G185T factor XIII: OR, 1.2; CI, 0.9 to 1.6; and 4G/5G plasminogen activator inhibitor type 1: OR, 0.9; CI, 0.7 to 1.2), or homocysteine metabolism (C677T methylenetetrahydrofolate reductase: OR, 0.9; CI, 0.8 to 1.1) were associated with an increased or decreased risk of myocardial infarction.

CONCLUSIONS

This study provides no evidence supporting an association between 9 polymorphisms of genes encoding proteins involved in hemostasis and the occurrence of premature myocardial infarction or protection against it.

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.

Genetic variants of the hemostatic system and development of transplant coronary artery disease

BACKGROUND

The occurrence of coronary artery disease (CAD) after heart transplantation may represent an accelerated inflammatory and thrombotic response to coronary vascular endothelial cell injury. Several common mutations involving hemostasis and cellular adhesion proteins have been associated with genetic susceptibility to native coronary heart disease. The clinical setting of heart transplantation provides a unique opportunity to examine the relative contribution of circulating (i.e., recipient) vs local vascular (i.e., donor) hemostatic components to the occurrence of CAD.

METHODS

We performed genotyping for several common hemostatic polymorphisms among 53 cardiac transplant patients and their heart donors. Patients were observed for an average of 43 months, and the presence of transplant CAD was determined by coronary angiography.

RESULTS

The development of transplant CAD did not relate to recipient hemostatic genotype, but 2 donor polymorphisms (PAI-1 4G/5G and alpha(2) integrin C807T) were important predictors of transplant CAD. The risk ratio (RR) of transplant CAD associated with donor PAI-1 4G/4G genotype was 2.6 (95% confidence interval [CI] 1.1-6.2) and was modified by recipient cytomegalovirus status, hyperlipidemia, diabetes, and recipient factor XIII Val34Leu genotype. The RR of transplant CAD associated with donor alpha(2) integrin 807 T/T genotype was 7.4 (95% CI, 2.5-22.0).

CONCLUSIONS

Genetic and metabolic factors contributed by both donor and recipient may interact at the level of the coronary vessel wall in the development of transplant-associated CAD, and this finding may provide additional support for the importance of local thrombotic response to endothelial injury in the pathogenesis of this disorder.

Iron deficiency anaemia in young women

OBJECTIVES

The expression density of GPIaIIa, the primary platelet collagen receptor (integrin alpha2beta1), is linked to two polymorphisms (GPIa-807C/T and HPA-5a/b). During evolution a gene shift from the genotypes GPIa-807CC-HPA-5bb to the genotypes GPIa-807CT-HPA-5aa has taken place. The aim of the study was to assess whether iron deficiency anaemia (e.g. increased blood loss) in young women could be associated with a specific genotype, indicating a role as potential evolutionary selection factor.

STUDY DESIGN

Women between 18 and 40 yr of age presenting for their first blood donation were asked about alimentary habits and use of oral contraception. Haemoglobin and serum ferritin were measured and the GPIa-C807T and HPA-5 genotypes were determined.

RESULTS

Two hundred women were included and grouped according to the WHO definition for iron deficiency anaemia (haemoglobin <121 g L(-1) and ferritin <15 microg L(-1)). Eight women fulfilled both WHO-criteria for iron deficiency anaemia, 145 women fulfilled none. No differences regarding age, use of oral contraceptives, alimentary habits, and HPA-5 were found between the groups. The GPIa-807CC genotype was strongly over-represented in the WHO-anaemic women as compared to the non-WHO-anaemic women (87.5% vs. 33.1%, P=0.003).

CONCLUSION

Iron deficiency anaemia in young women might have been the evolutionary disadvantage causing the gene shift from GPIa-807CC to 807CT.

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.

Allele-dependent transcriptional regulation of the human integrin alpha2 gene

Genetically controlled variation in alpha2beta1 expression by human blood platelets was previously described. Sixty-two haplotype sequences corresponding to the proximal 5' regulatory region (-1096 to +1) of the alpha2 gene were compared, and a dimorphic sequence -52C>T was identified that is located precisely between 2 tandem Sp1/Sp3 binding elements previously shown to be absolutely required for transcriptional activity of this gene in epithelial cell lines and the erythroleukemic cell line K562. The gene frequency of -52T in a random Caucasian population is approximately 0.35, and the expression of -52T correlates directly with reduced densities of platelet alpha2beta1. In mobility shift analyses, the -52T substitution attenuates complex formation with both Sp1 and Sp3. When transfected into the erythroleukemia cell line Dami, promoter-luciferase constructs bearing the -52T sequence exhibit a 5-fold decrease in activity relative to the -52C construct. In transfected CHRF-288-11 megakaryocytic cells, the corresponding activity decreases by 10-fold. The -52T sequence appears to be in linkage disequilibrium with the previously defined allele A3 (807C; HPA-5b), known to be associated with diminished expression of platelet alpha2beta1. In summary, a natural dimorphism has been identified within the proximal 5' regulatory region of the human integrin alpha2 gene that is responsible for decreased expression levels of the integrin alpha2beta1 on blood platelets through a mechanism that is probably mediated by the nuclear regulatory proteins Sp1 and Sp3.

Genetic variants of platelet glycoprotein receptors and risk of stroke in young women

BACKGROUND AND PURPOSE

A number of studies have examined the relationship between genetic platelet glycoprotein variants and early-onset atherothrombotic disease, particularly acute myocardial infarction. Data on the association of these genetic susceptibility markers with ischemic stroke are more limited, and their role in hemorrhagic stroke has not been previously examined.

METHODS

We performed genotype analysis for 5 common diallelic platelet glycoprotein polymorphisms in a population-based study of 78 white women aged <45 years with arterial stroke (36 ischemic cases and 42 hemorrhagic cases) and 346 demographically similar control subjects.

RESULTS

The 807T variant of glycoprotein Ia was associated with a 2-fold increased risk of ischemic stroke (age-adjusted odds ratio [OR]=2.24; 95% CI=0.99 to 5.06). The Met(145) allele of glycoprotein Ibalpha was associated with a trend toward an increased risk of ischemic stroke that was more pronounced in the homozygous state (OR=10.36), but the CI is extremely wide because of the small numbers of subjects (95% CI=1.43 to 79.34). Homozygosity for the Ser(843) allele of the glycoprotein IIb was associated with an approximately 5-fold increased risk of ischemic stroke among subgroups of women who carried a diagnosis of hypertension or diabetes (OR=4.51; 95% CI=1.01 to 20.13) or had elevated plasma homocysteine levels (OR=5.94; 95% CI=1.53 to 23.05). The genotype distributions for all 5 platelet glycoprotein polymorphisms were similar among hemorrhagic stroke cases and controls.

CONCLUSIONS

Several inherited platelet glycoprotein variants may be associated with an increased risk of ischemic stroke in young women. These associations seemed to be confined to women with other cardiovascular risk factors. Additional studies involving larger numbers of subjects are needed to confirm these preliminary findings.

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.

Association between diabetic retinopathy and genetic variations in α2β1 integrin, a platelet receptor for collagen

Platelets might be involved in the pathogenesis of diabetic microangiopathy. Wide interindividual variations in the density of a platelet collagen receptor (2β1 integrin or glycoprotein Ia/IIa) are reportedly associated with polymorphism(s) in the gene encoding the  subunit of the receptor, including a Bgl II polymorphism in intron 7. The aim of the present study was to determine the relationship between the Bgl II polymorphism and the susceptibility to diabetic microangiopathy. A case-control study comparing 227 patients with type II diabetes mellitus (119 with versus 108 without diabetic retinopathy) as well as 169 nondiabetic subjects demonstrated that genotypes with Bgl II (+) allele had a significant increase in the risk for retinopathy. The odds ratio for Bgl II (+/+) to Bgl II (−/−) was 3.41 (95% CI, 1.49-7.78, P = .0036) when analysis was confined to those with a disease duration of diabetes of 10 years or more. The present study suggests that the presence of a Bg II (+) allele is a genetic risk factor for diabetic retinopathy.

Allelic distribution of the glycoprotein Ia (alpha2-integrin) C807T/G873A dimorphisms among caucasian venous thrombosis patients and six racial groups

Two linked silent dimorphisms, 807 C --> T (Phe224) and 873 G --> A (Thr246) within the glycoprotein Ia (GPIa) gene have been correlated with low and high platelet receptor density, respectively, and associated with vascular disease. A multiplexed allele-specific PCR assay was used to determine the GPIa 807T/873A allele frequency among 331 Caucasian venous thrombosis patients and 3571 unrelated individuals belonging to six different racial groups. The 807T/873A allele frequencies were 54%, 51%, 39%, 39%, 38%, 34% and 30% among Native Americans, Hispanics, Caucasians, Caucasian venous thrombosis patients, Asian Indians, African-Americans, and Koreans, respectively. Significant differences in the GPIa allele frequency among racial groups were revealed which emphasized the need for appropriate controls in studies evaluating the association of GPIa genotype to vascular disease.

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

The platelet collagen receptor, GPIa/IIa, is an important mediator of platelet adhesion to fibrillar collagens at sites of vascular injury. Recently, a dimorphism at nucleotide 807 of the GPIa cDNA (TTC/TTT in codon 224) was shown to be associated with variation in GPIa/IIa receptor density on the platelet surface. We conducted a case-control study to determine if the 807T allele, linked with increased GPIa/IIa density, contributed to risk of myocardial infarction (MI). DNA from 546 acute MI cases and 507 controls, all aged <75 years, was genotyped for the C807T dimorphism using the TaqManTM system of allelic discrimination. The allelic odds ratio (OR) for MI in the complete cohort was 0.88 (95% CI 0.74-1.05, P = 0.17), indicating that the 807T allele was not associated with an increased risk of MI. There was also no increased risk of MI associated with the homozygous 807TT (P = 0.22) or heterozygous 807CT (P = 0.24) genotypes or for carriers of the 807T allele in any cohort subgroup analysed. We conclude that the GPIa 807T allele is not a risk factor for MI in our population either alone or in combination with other major cardiovascular risk factors.