Platelet glycoprotein Ibalpha Kozak polymorphism is associated with an increased risk of ischemic stroke

Platelet glycoprotein polymorphisms: risk, in vivo expression and severity of atherothrombotic stroke in Chinese

BACKGROUND

Polymorphisms in platelet glycoprotein (GP) receptors Ia, Ib and IIIa may be heritable risk factors for platelet-dependent thrombosis leading to death. The precipitation of stroke by occlusive thrombi has led to the investigation of the platelet surface GP receptors, that are involved in critical steps in the activation of platelets. Three polymorphisms in the GP Iba gene and one in each of GPIIIa, GP Ia were selected based on the evidence of functional effects on structure or expression as candidates for risk. We also determined whether these polymorphisms were associated with in vivo expression levels of platelet GP receptors and the severity of the neurological deficit.

METHODS

A Chinese hospital-based case-control study was conducted with 119 cases of atherothrombotic stroke and 166 age and sex matched controls. Genotyping was performed on lymphocyte DNA by standard methods and platelet GP expression levels were measured by flow-cytometry.

RESULTS

Allele and genotype frequencies of the GP receptor polymorphisms differ considerably between ethnic populations. We found the D allele of the GP Iba VNTR polymorphism was significantly associated with atherothrombotic stroke in our Chinese cohort, however we did not find a relationship among these polymorphisms, the expression levels of GP receptors and severity of the neurological deficit.

CONCLUSIONS

In our Chinese cohort the D allele of the GP Iba VNTR polymorphism is associated with atherothrombotic stroke. The number of VNTR repeats alters the length of amino acid sequence, which might affect the structure and function of this receptor.

Genetic analysis of HLA, NA and HPA typing in type 2 diabetes and ASO

We examined the genetic status of human leucocyte antigens (HLA), human platelet alloantigens (HPA) and neutrophil-specific antigens (NA) in patients with type 2 diabetes mellitus and diabetic arteriosclerosis obliterans (ASO). To our knowledge, the present study is the first report showing the relationship among three genetic factors in type 2 diabetes mellitus and ASO patients. HLA typing was performed by the polymerase chain reaction (PCR)-restriction fragment length polymorphism method. HPA-typing and NA-typing were by a PCR-sequence-specific primer method. The incidence of HLA-DRB1*1501 was found to be significant in type 2 diabetes and non-diabetic, particularly ASO-positive patients, compared to control subjects. There were no differences in NA1/NA2 between the control and diabetic or non-diabetic ASO groups. However, the frequency of NA2/NA2 in ASO-positive diabetes and non-diabetic ASO patients was significantly higher than controls. The a/b genotype of HPA-5a/5b was significantly lower in type 2 diabetes and non-diabetic ASO-positive patients than in controls. These findings suggest that genetic studies of HLA, NA and HPA could be useful to understand the pathogenesis of type 2 diabetes and ASO.

Gene polymorphism of platelet glycoprotein I balpha in Chinese patients with large- and small-artery subtypes of ischemic stroke

The platelet surface glycoprotein (GP) I balpha, an important part of the GP I b-IX-V complex, participates in the formation of thrombosis by initially mediating platelet adhesion under high shear stress. The purpose of present study was to investigate the association between gene polymorphism of GP I balpha (human platelet antigen 2, HPA2) and ischemic stroke in a matched case-control study. One hundred patients and 100 matched controls were enrolled in the study. The cases were divided into large- and small-vessel subtypes of ischemic stroke according to Trial of Org10172 in Acute Stroke Treatment criteria. Genotyping for GP I balpha polymorphism was documented by polymerase chain reaction amplification and restriction enzyme analysis. There were no statistically significant differences in the GP I balpha HPA2 genotype distribution between ischemic stroke group, large-vessel subtype group, small-vessel subtype group and corresponding control groups. The heterozygote genotype of GP I balpha HPA2 was more frequent in the large-vessel subtype group (16.1%) than in the small-vessel subtype group (10.1%), but the difference was not statistically significant. Ourresults suggest that the polymorphism of the GP I balpha HPA2 genotype might not be a genetic risk factor of ischemic stroke.

Fine mapping and evaluation of candidate genes for cervical cancer on 11q23

We previously showed that loss of heterozygosity (LOH) at 11q23 is a common genetic alteration in cervical cancer (CC) and that it correlates with extensive invasion of lymph-vascular spaces. In the current study, we looked for allelic loss in paired normal/tumor genomic DNA from 121 cervical tumors by using 20 well-mapped microsatellite markers on 11q. LOH at one or more loci was observed in 81 (66.9%) tumors. The deletion patterns in tumors are complex. However, at least three LOH islands could be defined between D11S614 and D11S4167. We also genotyped 11 CC cell lines and analyzed the results using the homozygosity mapping-of-deletions method. Five of the 11 cell lines showed continuous homozygosity that extended through 11q23.3-11q24.1. We used a candidate-gene approach to screen candidate tumor-suppressor genes (TSGs) that were localized in that region. Intragenic changes in the entire coding sequence of four candidate genes (RNF26, USP2, POU2F3, and TRIM29) in the region and a proposed TSG (PPP2R1B) centromeric to the region were evaluated. The expression status of USP2, POU2F3, TRIM29, and another proposed TSG that is telomeric to the region (BCSC1) also was examined. We identified previously described single-nucleotide polymorphisms (SNPs), several novel variants, and three rare SNPs in the five candidate genes. Decreased expression of POU2F3 and TRIM29 was found in some cervical tumors and CC cell lines. Our results indicate that a major region of LOH in cervical cancer exists within a 3.6-Mb stretch of DNA on 11q23.3-q24.1 and that somatic mutations in RNF26, USP2, TRIM29, POU2F3, or PPP2R1B probably are not important for cervical carcinogenesis.

A part le fibrinogène, les facteurs/marqueurs d’hémostase ont-ils aussi une place pour évaluer le risque d’accident cardiovasculaire ischémique ?

Most cardiovascular events result from a thrombotic complication of atherosclerotic lesions. In arterial vessels such as the coronary bed, an interrelationship of haemostatic, coagulation and fibrinolytic factors is implicated. While it can be demonstrated that fibrinogen is a risk factor/marker, the role of other factors is not well established. Under arterial flow conditions, platelets are predominantly involved in the thrombotic reaction. Yet, apart from a large increase in the platelet count, the involvement of platelet parameters in cardiovascular risk is not clearly evident. The lack of definitive platelet markers is at least partly due to the difficulty of studying platelet function ex vivo. Several polymorphisms of platelet glycoproteins carrying a moderate increase in risk have been reported, but only in younger patients. One potentially important factor for coagulation is the fibrin structure, which is dependent on fibrinogen, the rate of thrombin generation, the activity of factor XIII and the interrelationship of the cells concerned, all of which act on its sensitivity to thrombosis. Coagulation factors largely affect the rate of thrombin generation. The activity of the fibrinolytic system (and principally any deficiency) has a role in the cardiovascular risk. General markers of cardiovascular risk such as D-dimers are potentially useful, but they increase with thrombin generation and are decreased by a deficiency in fibrinolysis. Furthermore, possibly because they are not indicative of the fibrin structure, they are poorly correlated with clinical events. The poor significance of the available haemostatic, coagulation and/or fibrinolytic parameters is probably due to their lack of representativeness, since haemostatic, coagulation and fibrinolytic systems are all involved in the thrombotic response (and some in atherogenesis itself). Atherogenesis is a multifactorial process and numerous moderate risk factors act in association. Better predictability of the haemostatic tests would probably result from both the design of more representative tests and the evaluation of multiple parameters, and would lead to the definition of a risk score. Technological advances will make this possible.

Genetic variability of platelet glycoprotein Ibalpha gene

Platelet membrane glycoprotein (GP) Ibalpha is a critical component of platelet adhesion complex to subendothelium structures following tissue injury or pathological surfaces, such as atherosclerotic plaques. Polymorphisms of the GPIbalpha gene have been associated with a high risk for occlusive vascular disease, and its distribution varies considerably among distinct populations. These polymorphisms comprise the human platelet antigen (HPA)-2 system, the -5C/T dimorphism of the Kozak sequence, and the variable number of tandem 39-bp repeats (VNTR). Here we report the prevalence of the GPIbalpha gene polymorphisms among Brazilians, a highly ethnically diverse population. We analyzed 492 subjects of European, African, or Indigenous origin. It was possible to determine ten distinct haplotypes. The most common ( reverse similar 40%) haplotype was the Kozak-TT/HPA-2aa/VNTR-CC for both Caucasian and African descent. However, among Indigenous, Kozak-TT/HPA-2aa/VNTR-CC and Kozak-TC/HPA-2aa/VNTR-CC were equally present. Although a strong linkage disequilibrium between VNTR and HPA-2 polymorphism had also been observed, here we determined incomplete linkage disequilibrium in 10% of subjects from all ethnic groups. VNTR-E, a rare variant lacking the 39-bp repeat, was identified in two unrelated subjects, and functional platelet studies revealed no abnormalities. The VNTR-A allele, the largest variant containing four copies of the repeats, was not identified in this population. However, homozygosity for the VNTR-A allele (Kozak-TT/HPA-2aa/VNTR-AA) was determined in two distinct species of nonhuman primates. These results suggest a greater complex evolutionary mechanism in the macroglycoprotein region of the GPIbalpha gene and may be useful in the design of gene-disease association studies for vascular disease.

Vienna Stroke Registry. Impact of the platelet glycoprotein Ib alpha Kozak polymorphism on the risk of ischemic cerebrovascular events

We performed a multicenter case-control study to evaluate the impact of the glycoprotein 1b alpha (-5)T/C Kozak polymorphism on the risk of ischemic cerebrovascular events. The genetic analysis in 1399 patients (745 men; median age, 70 years; interquartile ratio, 58-78) and 1066 control subjects (549 men; median age, 47 years; interquartile ratio, 39-59) was carried out with mutagenically separated polymerase chain reaction. Homozygous C/C genotype carriers had a 3.5-fold increased risk for ischemic cerebrovascular events (95% confidence interval, 1.5-7.9, P = 0.003) over T/T or T/C genotype carriers together. The effect was independent of well-established atherosclerotic risk factors. Our findings could be explained by the reported gene dose effect of the Kozak polymorphism on the density of the glycoprotein 1b alpha/IX/V receptors on platelets. According to our data, the (-5)C Kozak allele may represent a candidate genetic susceptibility factor for ischemic cerebrovascular events.

Epratuzumab in non-hodgkin’ lymphomas

Non-Hodgkin's lymphomas (NHL) are a diverse group of malignancies that result, in addition to their treatments, in significant morbidity and mortality in the population. The identification of more effective and better tolerated treatments is of vital importance. Immunotherapy using monoclonal antibodies directed against the CD20 protein has had a profound impact on the management of patients with B-cell NHL. Additional antigen targets are being aggressively investigated. The targeting of lymphoma cells with monoclonal antibodies offers a treatment with a potentially noncross-resistant mechanism of action and a more favorable toxicity profile compared to chemotherapy. Epratuzumab (humanized LL2) is a humanized immunoglobulin G1 monoclonal antibody directed against the CD22 protein in which expression is restricted to mature B cells. Because of important differences in the characteristics of CD22 compared to CD20, epratuzumab may become an important component of future therapies for NHL.

Stroke in patients with heparin-induced thrombocytopenia and the effect of argatroban therapy

OBJECTIVE

To investigate the frequency, mortality rate, and characteristics of stroke in heparin-induced thrombocytopenia and the effect of argatroban therapy in that setting.

DESIGN

Retrospective analysis of two prospective studies of argatroban therapy in heparin-induced thrombocytopenia.

SETTING

Hospitalized care.

PATIENTS

Patients were 960 patients with heparin-induced thrombocytopenia (767 argatroban-treated patients, 193 historical controls).

INTERVENTIONS

Argatroban 2 microg x kg x min, adjusted to achieve activated partial thromboplastin times 1.5-3 times baseline

MEASUREMENTS AND MAIN RESULTS

Case records were reviewed to identify patients with stroke present at or within 37 days of study entry and to assess 37-day outcomes. Stroke occurred in 30 (3.1%) patients (stroke at entry, n = 9; new stroke during follow-up, n = 24; more than one stroke, n = 4). By logistic regression with treatment, protocol, age, and gender as covariates, females were significantly more likely to suffer stroke (odds ratio, 2.48; 95% confidence interval, 1.11-5.53; p =.026) and stroke-associated mortality (odds ratio, 4.10; 95% CI, 1.12-15.01; p =.033), and argatroban-treated patients had significantly reduced odds, vs. control, of new stroke (odds ratio, 0.31; 95% confidence interval, 0.10-0.96; p =.041) and stroke-associated mortality (odds ratio, 0.18; 95% confidence interval, 0.03-0.92; p =.039). Stroke (odds ratio, 3.66; 95% confidence interval, 1.73-7.73; p <.001) and age (odds ratio per year, 1.017; 95% confidence interval, 1.004-1.029; p =.008) were significant predictors of all-cause death. In the argatroban group, baseline platelet counts were significantly less in patients with, vs. without, stroke (medians, 42 x 10/L vs. 72 x 10/L; p =.006). Of 35 stroke events, 33 (94%) were ischemic and two (6%) were hemorrhagic (one per group, none during argatroban infusion); 30 (86%) were present at or within 13 days of entry.

CONCLUSIONS

Stroke, particularly ischemic stroke, is common in heparin-induced thrombocytopenia and significantly increases mortality risk. Stroke in heparin-induced thrombocytopenia occurs most often in females, in patients with more severe thrombocytopenia, and within 2 wks of heparin-induced thrombocytopenia presentation. Argatroban therapy vs. control significantly reduces the likelihood of new stroke and stroke-associated mortality in heparin-induced thrombocytopenia without increasing intracranial hemorrhage.

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

OBJECTIVE

To evaluate the association between platelet glycoprotein polymorphisms and the risks of single and second eye involvement with nonarteritic anterior ischemic optic neuropathy (NAION).

DESIGN

Case-control study.

PARTICIPANTS

Ninety-two consecutive patients with NAION, 26 of whom had second eye involvement, and 145 controls who attended the eye clinic for nonvascular entities.

METHODS

Polymerase chain reactions and restriction enzyme analyses were performed for genotyping 5 platelet glycoprotein polymorphisms on DNA extracted from whole blood.

MAIN OUTCOME MEASURES

Frequencies of the various platelet polymorphisms.

RESULTS

One of the 5 platelet glycoprotein polymorphisms analyzed, the B allele of the glycoprotein Ibalpha variable number of tandem repeats (VNTR), was a significant independent risk factor for NAION, with an odds ratio of 4.25 and a 95% confidence interval of 1.67 to 10.82 (P = 0.0026). All other platelet glycoprotein polymorphisms were similarly distributed in patients and controls. In addition, 9 of 16 patients who bore the VNTR B allele (56.3%) had second eye involvement, whereas among patients not harboring the VNTR B allele only 17 of 72 patients (23.6%) had second eye involvement (P = 0.009). Moreover, second eye involvement occurred earlier in patients who bore the specific polymorphism.

CONCLUSIONS

The presence of the VNTR B allele of glycoprotein Ibalpha confers a significant risk for NAION and predisposes affected patients to second eye involvement.

Role of platelet glycoprotein polymorphisms in cardiovascular diseases

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

Antiplatelet therapy: in search of the 'magic bullet'

The central importance of platelets in the development of arterial thrombosis and cardiovascular disease is well established. No other single cell type is responsible for as much morbidity and mortality as the platelet and, as a consequence, it represents a major target for therapeutic intervention. The growing awareness of the importance of platelets is reflected in the increasing number of patients receiving antiplatelet therapy, a trend that is likely to continue in the future. There are, however, significant drawbacks with existing therapies, including issues related to limited efficacy and safety. The discovery of a 'magic bullet' that selectively targets pathological thrombus formation without undermining haemostasis remains elusive, although recent progress in unravelling the molecular events regulating thrombosis has provided promising new avenues to solve this long-standing problem.

von Willebrand factor but not alpha-thrombin binding to platelet glycoprotein Ibalpha is influenced by the HPA-2 polymorphism

OBJECTIVE

Glycoprotein (GP) Ibalpha is the functionally dominant subunit of the platelet GPIb-IX-V receptor complex. The N-terminal domain of the GPIbalpha chain contains binding sites for alpha-thrombin and von Willebrand factor (VWF). The human platelet alloantigen (HPA)-2 polymorphism of the GPIbalpha gene is associated with a C/T transition at nucleotide 1018, resulting in a Thr/Met dimorphism at residue 145 of GPIbalpha. To study the structural and functional effects of this dimorphism, N-terminal fragments (AA1-289) of the HPA-2a and HPA-2b alloform of GPIbalpha expressed in CHO cells were used.

METHODS AND RESULTS

Of 74 moAbs directed against human GPIbalpha, 2 antibodies with epitope between AA1-59 could differentiate between both alloforms. In addition, VWF bound with a higher affinity to the recombinant HPA-2a fragment or to homozygous HPA-2a platelets. In contrast, no difference was found in the binding of alpha-thrombin to the recombinant alloform fragments or of antibodies directed against the alpha-thrombin binding anionic sulfated tyrosine sequence (AA269-282).

CONCLUSIONS

Whereas the Thr145Met dimorphism does not affect alpha-thrombin binding, it does influence the conformation of the N-terminal flanking region and first leucine-rich repeat of GPIbalpha and by this has an effect on VWF binding.

Glycoprotein Ib polymorphisms influence platelet plug formation under high shear rates

Platelet polymorphisms (Kozak, VNTR and HPA-2) within glycoprotein (GP)Ib alpha may be associated with an increased risk of arterial thrombosis. However, the functional role of these polymorphisms has not been clarified. Their influence on platelet plug formation under high shear rates was, therefore, examined in 233 healthy individuals. Collagen-adrenaline-induced closure time was shorter in carriers of the C/D versus C/C VNTR allele and in homozygotes with the (-5)T/T versus (-5)C/T Kozak genotype as determined by novel polymerase chain reaction methods. The HPA-2 genotype had no effects, and the density of GPIb alpha molecules was not influenced by GPIb alpha genotypes.

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

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

Addressing the heterogeneity of the ischemic stroke phenotype in human genetics research

BACKGROUND AND PURPOSE

Many investigators have approached ischemic stroke as a complex phenotype by dividing the ischemic stroke population into distinct subtypes. The purpose of this study was to review systematically the methods used to subtype ischemic stroke in recent genetic studies.

METHODS

The MEDLINE database was searched for articles pertaining to research on the genetics of human ischemic stroke published from January 2000 through January 2002. Abstracts and full-length reports were then sequentially screened to select articles pertaining to original case-control or cohort studies.

RESULTS

The initial search yielded 153 publications. Of 41 relevant articles, ischemic stroke was subtyped in 25 (61%). The most common standard subtyping system was the Cerebrovascular Classification of Diseases III system (9 articles). Of the subtyping systems used, 3 had previously published interrater reliability. The subtyping system was reported to have been prespecified in 1 study. Four articles reported using central adjudication. Two articles reported that the person doing the subtyping was blinded to genotype, and 2 reported that the person doing the genotyping was blinded to the patient's subtype status.

CONCLUSIONS

When investigators subtyped ischemic stroke, they typically used either nonstandard classification systems or systems of undetermined reliability. Important methodological issues, including blinding and prespecification of the classification system, were rarely reported. Advances in methodology and scientific reporting standards would foster identification of subtype-specific genetic risk factors.

Stroke: a review with an African perspective

The frequency of stroke and stroke-associated mortality are higher in Blacks than in other races. Several of the known risk factors for stroke, such as hypertension, diabetes and obesity, are more common in Blacks than Whites, and sickle-cell disease and HIV infection are stroke risk factors with particular relevance to Africans. Although the facilities for accurate stroke diagnosis and classification are unavailable in most parts of Africa, careful analysis of the clinical features can minimize the rates of misdiagnosis and misclassification. The high levels of stroke-attributable morbidity and mortality observed in Africans could be markedly reduced by instituting primary and secondary preventive measures and by educating health-care professionals on stroke-management strategies.

Common variations in platelet glycoproteins: pharmacogenomic implications

Atherosclerosis and its complications are the result of complex interactions between the environment and genetic factors. Platelets play an important role in this disease process and antiplatelet agents are an essential part of its treatment. However, individual response to antiplatelet therapy is variable and agents that are safe and effective in one individual may be ineffective or harmful in another. It is likely that genetic factors are involved in this variance as platelet, and platelet-associated proteins are highly polymorphic. Up to 30% of natural variation in platelet reactivity is related to genetic inheritance. Rare inherited defects of platelet function due to the absence or reduced surface expression of platelet adhesion receptors have long been recognised. These cause minor bleeding defects and are usually clinically apparent. Antiplatelet agents should be avoided in these situations. The importance of the more common genetic variations or polymorphisms, which result in minor changes in the expressed protein and are often clinically silent, is unknown. Investigations are ongoing into the role of this variation in platelet physiology. A number of polymorphisms in platelet surface glycoproteins have received particular attention; the (A1/2) polymorphism resulting in conformational change at the amino terminus of the beta-3 chain of the platelet fibrinogen receptor glycoprotein (GP) IIb/IIIa and polymorphisms in the platelet collagen (GPIa/IIa and GPVI) and von Willebrand receptors (GPIb-IX). The (A2) allele has been associated with resistance to the antiplatelet agent aspirin and increased platelet responsiveness. The GPIa polymorphism has been associated with increased surface expression of GPIa and increased platelet adhesion to collagen. Recently, conflicting reports of the association of these polymorphisms with coronary artery disease (CAD) and its complications have been described. Mutations have also been identified in other platelet surface receptors including the recently identified G(i)-linked platelet adenosine diphosphate (ADP) receptor (P2Y(12)), targeted by the antiplatelet agents ticlopidine and clopidogrel. These discoveries have stimulated interest in the role of genetic factors in platelet physiology. In this article, the current knowledge of the influence of genetic make-up on antiplatelet therapy is discussed.