A meta-analysis of the angiotensin-converting enzyme gene polymorphism and restenosis after percutaneous transluminal coronary revascularization: evidence for publication bias

Association of Endothelial Nitric Oxide Synthase and Angiotensin-Converting Enzyme Genes Polymorphism With In-Sent Restenosis of Bare Metal Stents vs Drug-Eluting Stents in Egyptians

Despite its unequivocal superiority compared with balloon angioplasty, coronary stenting did not abolish restenosis. We aimed to evaluate the associations between a common single nucleotide polymorphism occurring in endothelial nitric oxide synthase (eNOS) and angiotensin-converting enzyme (ACE) genes and the risk of in-stent restenosis (ISR) of bare metal stents vs drug-eluting stents (BMS vs DES) implanted in Egyptian patients. Two hundred patients who had coronary stenting were divided into group I (n = 98) who received a BMS and group II (n = 102) who received a DES. eNOS and ACE genes polymorphism were analyzed by polymerase chain reaction (PCR). We found that the GA and AA genotypes of the eNOS gene were associated with the ISR with both BMS and DES. However, the ACE gene was not associated with ISR. We concluded that eNOS gene polymorphism is associated with ISR. Hypertension, stent length, and AA genotype of the eNOS gene were found to be independent predictors of the occurrence of ISR after both BMS and DES use.

Impact of I/D polymorphism of angiotensin-converting enzyme (ACE) gene on myocardial infarction susceptibility among young Moroccan patients

Objective

Our case–control study aimed to access the potential association of insertion/deletion (I/D) ACE (angiotensin converting enzyme) gene polymorphism with myocardial infarction (MI) risk of occurrence among a sample of Moroccan patients, especially young ones.

Results

Distribution of I/D ACE gene variant among cases vs controls, showed that healthy controls carried out higher frequency of wild type allele I compared to cases (23.5% vs 21.79% respectively), when cases were carrying higher frequency of mutant allele D (78.21% vs 76.5% for controls). Patients were-after this- divided into two groups of < 45 and > 55 years of age, to investigate whether or not younger patients carried out higher frequency of the mutant allele D, than older ones. As expected, < 45 years old patients carried out more DD genotype than older ones (68.9% vs 54.6% respectively), and higher frequency of mutant allele D (81.08% vs 75% respectively). Besides, a tendency to a positive association was found under the recessive genetic transmission model (OR [95% CI] = 1.85 [0.93–3.69], P = 0.08), suggesting that the I/D ACE polymorphism may be associated with MI occurrence among younger patients (< 45 years of age).

Electronic supplementary material

The online version of this article (10.1186/s13104-017-3039-1) contains supplementary material, which is available to authorized users.

Contextualizing Genetics for Regional Heart Failure Care

Congestive heart failure (CHF) is a chronic and often devastating cardiovascular disorder with no cure. There has been much advancement in the last two decades that has seen improvements in morbidity and mortality. Clinicians have also noted variations in the responses to therapies. More detailed observations also point to clusters of diseases, phenotypic groupings, unusual severity and the rates at which CHF occurs. Medical genetics is playing an increasingly important role in answering some of these observations. This developing field in many respects provides more information than is currently clinically applicable. This includes making sense of the established single gene mutations or uncommon private mutations. In this thematic series which discusses the many factors that could be relevant for CHF care, once established treatments are available in the communities; this section addresses a contextual role for medical genetics.

Genetic markers: Potential candidates for cardiovascular disease

The effective prevention of cardiovascular disease depends upon the ability to recognize the high-risk individuals at an early stage of the disease or long before the development of adverse events. Evolving technologies in the fields of proteomics, metabolomics, and genomics have played a significant role in the discovery of cardiovascular biomarkers, but so far these methods have achieved the modest success. Hence, there is a crucial need for more reliable, suitable, and lasting diagnostic and therapeutic markers to screen the disease well in time to start the clinical aid to the patients. Gene polymorphisms associated with the cardiovascular disease play a decisive role in the disease onset. Therefore, the genetic marker evaluation to classify high-risk patients from low-risk patients trends an effective approach to patient management and care. Currently, there are no genetic markers available for extensive adoption as risk factors for coronary vascular disease, yet, there are numerous promising, biologically acceptable candidates. Many of these gene biomarkers, alone or in combination, can play an essential role in the prediction of cardiovascular risk. The present review highlights some putative emerging genetic biomarkers that could facilitate more authentic and fast diagnosis of CVD. This review also briefly describes few technological approaches employed in the biomarker search.

Pharmacogenomics and cardiovascular disease

Variability in drug responsiveness is a sine qua non of modern therapeutics, and the contribution of genomic variation is increasingly recognized. Investigating the genomic basis for variable responses to cardiovascular therapies has been a model for pharmacogenomics in general and has established critical pathways and specific loci modulating therapeutic responses to commonly used drugs such as clopidogrel, warfarin, and statins. In addition, genomic approaches have defined mechanisms and genetic variants underlying important toxicities with these and other drugs. These findings have not only resulted in changes to the product labels but also have led to development of initial clinical guidelines that consider how to facilitate incorporating genetic information to the bedside. This review summarizes the state of knowledge in cardiovascular pharmacogenomics and considers how variants described to date might be deployed in clinical decision making.

Genetic causation of neointimal hyperplasia in hemodialysis vascular access dysfunction

The major cause of hemodialysis vascular access failure is venous stenosis resulting from neointimal hyperplasia. Genetic factors have been shown to be associated with cardiovascular disease and peripheral vascular disease (PVD) in the general population. Genetic factors may also play an important role in vascular access stenosis and development of neointimal hyperplasia by affecting pathways that lead to inflammation, endothelial function, oxidative stress, and vascular smooth muscle proliferation. This review will discuss the role of genetics in understanding neointimal hyperplasia development in hemodialysis vascular access dysfunction and other disease processes with similar neointimal hyperplasia development such as coronary artery disease and PVD.

Restenosis after PCI. Part 1: pathophysiology and risk factors

Restenosis is a complex disease for which the pathophysiological mechanisms have not yet been fully elucidated, but are thought to include inflammation, proliferation, and matrix remodeling. Over the years, many predictive clinical, biological, (epi)genetic, lesion-related, and procedural risk factors for restenosis have been identified. These factors are not only useful in risk stratification of patients, they also contribute to our understanding of this condition. Furthermore, these factors provide evidence on which to base treatment tailored to the individual and aid in the development of novel therapeutic modalities. In this Review, we will evaluate the available evidence on the pathophysiological mechanisms of restenosis and provide an overview of the various risk factors, together with the possible clinical application of this knowledge.

A genome-wide association study identifies a region at chromosome 12 as a potential susceptibility locus for restenosis after percutaneous coronary intervention

Percutaneous coronary intervention (PCI) has become an effective therapy to treat obstructive coronary artery diseases (CAD). However, one of the major drawbacks of PCI is the occurrence of restenosis in 5-25% of all initially treated patients. Restenosis is defined as the re-narrowing of the lumen of the blood vessel, resulting in renewed symptoms and the need for repeated intervention. To identify genetic variants that are associated with restenosis, a genome-wide association study (GWAS) was conducted in 295 patients who developed restenosis (cases) and 571 who did not (controls) from the GENetic Determinants of Restenosis (GENDER) study. Analysis of ~550 000 single nucleotide polymorphisms (SNPs) in GENDER was followed by a replication phase in three independent case-control populations (533 cases and 3067 controls). A potential susceptibility locus for restenosis at chromosome 12, including rs10861032 (P(combined) = 1.11 × 10(-7)) and rs9804922 (P(combined) = 1.45 × 10(-6)), was identified in the GWAS and replication phase. In addition, both SNPs were also associated with coronary events (rs10861032, P(additive) = 0.005; rs9804922, P(additive) = 0.023) in a trial based cohort set of elderly patients with (enhanced risk of) CAD (PROSPER) and all-cause mortality in PROSPER (rs10861032, P(additive) = 0.007; rs9804922, P(additive) = 0.013) and GENDER (rs10861032, P(additive) = 0.005; rs9804922, P(additive) = 0.023). Further analysis suggests that this locus could be involved in regulatory functions.

A systematic review on pharmacogenetics in cardiovascular disease: is it ready for clinical application?

Pharmacogenetics is the search for heritable genetic polymorphisms that influence responses to drug therapy. The most important application of pharmacogenetics is to guide choosing agents with the greatest potential of efficacy and smallest risk of adverse drug reactions. Many studies focusing on drug-gene interactions have been published in recent years, some of which led to adaptation of FDA recommendations, indicating that we are on the verge of the clinical application of genetic information in drug therapy. This systematic review provides a comprehensive overview of the current knowledge on pharmacogenetics of all major drug classes currently used in the treatment of cardiovascular diseases.

Quantitative trait locus analysis of neointimal formation in an intercross between C57BL/6 and C3H/HeJ apolipoprotein E-deficient mice

BACKGROUND

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit marked differences in neointimal formation after arterial injury when deficient in apolipoprotein E (apoE(-/-)) and fed a Western diet. Quantitative trait locus (QTL) analysis was performed on an intercross between B6.apoE(-/-) and C3H.apoE(-/-) mice to determine genetic factors contributing to the phenotype.

METHODS AND RESULTS

Female B6.apoE(-/-) mice were crossed with male C3H.apoE(-/-) mice to generate F(1)s, which were intercrossed to generate 204 male F(2) progeny. At 10 weeks of age, F(2)s underwent endothelium denudation injury to the left common carotid artery. Mice were fed a Western diet for 1 week before and 4 weeks after injury and analyzed for neointimal lesion size, plasma lipid and MCP-1 levels. One significant QTL, named Nih1 (61cM, LOD score: 5.02), on chromosome 12 and a suggestive locus on chromosome 13 (35cM, LOD: 2.67) were identified to influence lesion size. One significant QTL on distal chromosome 1 accounted for major variations in plasma non-HDL cholesterol and triglyceride levels. Four suggestive QTLs on chromosomes 1, 2, and 3 were detected for circulating MCP-1 levels. No correlations were observed between neointimal lesion size and plasma lipid levels or between lesion size and plasma MCP-1 levels.

CONCLUSIONS

Neointimal formation is controlled by genetic factors independent of those affecting plasma lipid levels and circulating MCP-1 levels in the B6 and C3H mouse model.

ACE (I/D) polymorphism and response to treatment in coronary artery disease: a comprehensive database and meta-analysis involving study quality evaluation

BACKGROUND

The role of angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism in modifying the response to treatment modalities in coronary artery disease is controversial.

METHODS

PubMed was searched and a database of 58 studies with detailed information regarding ACE I/D polymorphism and response to treatment in coronary artery disease was created. Eligible studies were synthesized using meta-analysis methods, including cumulative meta-analysis. Heterogeneity and study quality issues were explored.

RESULTS

Forty studies involved invasive treatments (coronary angioplasty or coronary artery by-pass grafting) and 18 used conservative treatment options (including anti-hypertensive drugs, lipid lowering therapy and cardiac rehabilitation procedures). Clinical outcomes were investigated by 11 studies, while 47 studies focused on surrogate endpoints. The most studied outcome was the restenosis following coronary angioplasty (34 studies). Heterogeneity among studies (p < 0.01) was revealed and the risk of restenosis following balloon angioplasty was significant under an additive model: the random effects odds ratio was 1.42 (95% confidence interval:1.07-1.91). Cumulative meta-analysis showed a trend of association as information accumulates. The results were affected by population origin and study quality criteria. The meta-analyses for the risk of restenosis following stent angioplasty or after angioplasty and treatment with angiotensin-converting enzyme inhibitors produced non-significant results. The allele contrast random effects odds ratios with the 95% confidence intervals were 1.04(0.92-1.16) and 1.10(0.81-1.48), respectively. Regarding the effect of ACE I/D polymorphism on the response to treatment for the rest outcomes (coronary events, endothelial dysfunction, left ventricular remodeling, progression/regression of atherosclerosis), individual studies showed significance; however, results were discrepant and inconsistent.

CONCLUSION

In view of available evidence, genetic testing of ACE I/D polymorphism prior to clinical decision making is not currently justified. The relation between ACE genetic variation and response to treatment in CAD remains an unresolved issue. The results of long-term and properly designed prospective studies hold the promise for pharmacogenetically tailored therapy in CAD.

Cuff-induced vascular intima thickening is influenced by titration of the Ace gene in mice

We tested the hypothesis that small changes in angiotensin I-converting enzyme (ACE) expression can alter the vascular response to injury. Male mice containing one, two, three, and four copies of the Ace gene with no detectable vascular abnormality or changes in blood pressure were submitted to cuff-induced femoral artery injury. Femoral thickening was higher in 3- and 4-copy mice (42.4 ± 4.3% and 45.7 ± 6.5%, respectively) compared with 1- and 2-copy mice (8.3 ± 1.3% and 8.5 ± 0.9%, respectively). Femoral ACE levels from control and injured vessels were assessed in 1- and 3-copy Ace mice, which represent the extremes of the observed response. ACE vascular activity was higher in 3- vs. 1-copy Ace mice (2.4-fold, P < 0.05) in the control uninjured vessel. Upon injury, ACE activity significantly increased in both groups [2.41-fold and 2.14-fold ( P < 0.05) for 1- and 3-copy groups, respectively] but reached higher levels in 3- vs. 1-copy Ace mice ( P < 0.05). Pharmacological interventions were then used as a counterproof and to indirectly assess the role of angiotensin II (ANG II) on this response. Interestingly, ACE inhibition (enalapril) and ANG II AT1 receptor blocker (losartan) reduced intima thickening in 3-copy mice to 1-copy mouse values ( P < 0.05) while ANG II treatment significantly increased intima thickening in 1-copy mice to 3-copy mouse levels ( P < 0.05). Together, these data indicate that small physiologically relevant changes in ACE, not associated with basal vascular abnormalities or blood pressure levels, do influence the magnitude of cuff-induced neointima thickening in mice.

ALOX5AP variants are associated with in-stent restenosis after percutaneous coronary intervention

BACKGROUND

Use of drug-eluting stents (DES) has reduced in-stent restenosis after percutaneous coronary intervention (PCI); however, DES are associated with late stent thrombosis. There is no accurate way to predict in-stent restenosis, although risk factors for atherosclerosis overlap those for in-stent restenosis. Therefore, we evaluated atherosclerosis candidate genes for association with in-stent restenosis.

METHODS

We identified 46 consecutive cases that had undergone PCI with bare-metal stents who subsequently developed symptomatic in-stent restenosis of the target lesion (>/=75% luminal narrowing) within 6 months. Forty-six age-, race-, vessel-diameter- and sex-matched controls without in-stent restenosis after PCI with bare-metal stent were also identified. Single-nucleotide polymorphisms (SNPs, N=82) from 39 candidate atherosclerosis genes were genotyped. Multivariable logistic regression models were used to test for association.

RESULTS

Five SNPs were associated with in-stent restenosis. Three ALOX5AP SNPs were most strongly associated, two with increased risk (OR 3.74, p=0.01; OR 3.46, p=0.02), and the third with decreased risk of in-stent restenosis (OR 0.09, p=0.004). Two ALOX5AP haplotypes were associated with in-stent restenosis (HapB: OR 3.13, p=0.03); and a haplotype similar to HapA: OR 0.14, p=0.0009).

CONCLUSIONS

ALOX5AP, a gene within the inflammatory leukotriene pathway linked to and associated with coronary atherosclerosis, is also associated with in-stent restenosis. Genotyping these variants may help identify those at risk for in-stent restenosis who would benefit most from use of DES.

Pharmacogenomics of Renin Angiotensin System Inhibitors in Coronary Artery Disease

Renin Angiotensin System (RAS) inhibitors comprise some of the most commonly used medications in coronary artery disease (CAD) and its related syndromes. Unfortunately, significant inter-patient variability seems likely in response to these agents; of which, the influence of genetic determinants is of interest. This review summarizes the available RAS inhibitor pharmacogenomic studies which have evaluated RAS polymorphisms that either elucidate mechanism via surrogate endpoint measurements, or predict efficacy via clinical outcomes in CAD related syndromes.Regardless of the endpoint, none of the RAS genotypes conclusively predicts efficacy of RAS inhibitors. In fact, the results of the pharmacogenomic studies were often in direct conflict with one another. Varied results appear due to methodological limitations (e.g., inadequate study power, genotyping error, methods of endpoint measurement), study conceptualization (e.g., overestimating the contribution of polymorphism to disease, lack of haplotype approach), and differences between studies (e.g., genotype frequency, study subject characteristics, the specific medication and dose used). Thus investigators should consider the various methodological limitations to improve upon the current approach to RAS inhibitor pharmacogenomic research in the vast CAD population.

The effect of HapMap on cardiovascular research and clinical practice

The Haplotype Genetic Map (HapMap) is an invaluable resource to the cardiovascular researcher, enabling a decrease in cost and an increase in the efficiency and speed of discoveries in the laboratory. As cardiologists, we need to understand the vocabulary of genomics because the translation of scientific findings using HapMap could provide insight for improved care and therapeutic guidance of our patients. Genomics is the evaluation of genes as a dynamic system, in which genes interact to influence biologic pathways, networks and physiology. The HapMap promises to increase the efficiency of genomics in identifying cardiovascular-disease-related genes that could become vital for choosing relevant tests and providing preventative and curative therapies. In this Review, the HapMap will be described, to provide insight into the relevance of this work to cardiovascular practice, to clinical research in cardiovascular disease and to future discoveries in diagnostic and therapeutic modalities.

Restenosis after percutaneous coronary intervention is associated with the angiotensin-II type-1 receptor 1166A/C polymorphism but not with polymorphisms of angiotensin-converting enzyme, angiotensin-II receptor, angiotensinogen or heme oxygenase-1

OBJECTIVES

The renin-angiotensin system (RAS) is thought to play a major role in the pathophysiology of de-novo restenotic lesions and in-stent restenosis after percutaneous coronary intervention (PCI). Heme oxygenase-1 (HO-1), is thought to beneficially influence these processes. We examined the effect of pharmacologic as well as genetic RAS interactions on restenosis in a large population of consecutive patients undergoing PCI, and evaluated possible gene-gene interactions in both systems.

METHODS

The GENDER project is a multicenter prospective follow-up study, including 3146 patients after successful PCI. Genotyping in these patients was performed for the ACE gene insertion/deletion, the angiotensinogen 235Met/Thr, T174M and A(-6)G, the angiotensin-II type 1 receptor (AT1R) 1166A/C and T810A, the angiotensin-II type 2 receptor (AT2R) 1675G/A and 3123A polymorphisms and the length polymorphism in the HO-1 promoter region.

RESULTS

A total of 3104 patients were followed for 10 months. In 2975 patients at least one of the nine genotypes could be determined. The AT1R 1166 CC genotype showed a significant association with TVR; the other polymorphisms did not. RAS-inhibitory drugs were not associated with the incidence of TVR, nor did they interact with any of the investigated polymorphisms. Patients with the ACE I/I polymorphism showed a trend towards a better outcome if they had a short number of repeats in the HO-1 promoter. This relationship was inversely present in carriers of the ACE D/D polymorphism.

CONCLUSION

We could only establish a role for the AT1R 1166A/C polymorphism in restenosis after PCI. However, significant gene-gene interaction was suggested for the ACE gene and the HO-1 promotor. The RAS and HO-1 relation in restenosis merits further investigation.

Endothelial dysfunction: a multifaceted disorder (The Wiggers Award Lecture)

Endothelial cells synthesize and release various factors that regulate angiogenesis, inflammatory responses, hemostasis, as well as vascular tone and permeability. Endothelial dysfunction has been associated with a number of pathophysiological processes. Oxidative stress appears to be a common denominator underlying endothelial dysfunction in cardiovascular diseases. However, depending on the pathology, the vascular bed studied, the stimulant, and additional factors such as age, sex, salt intake, cholesterolemia, glycemia, and hyperhomocysteinemia, the mechanisms underlying the endothelial dysfunction can be markedly different. A reduced bioavailability of nitric oxide (NO), an alteration in the production of prostanoids, including prostacyclin, thromboxane A2, and/or isoprostanes, an impairment of endothelium-dependent hyperpolarization, as well as an increased release of endothelin-1, can individually or in association contribute to endothelial dysfunction. Therapeutic interventions do not necessarily restore a proper endothelial function and, when they do, may improve only part of these variables.

Local literature bias in genetic epidemiology: an empirical evaluation of the Chinese literature

BACKGROUND

Postulated epidemiological associations are subject to several biases. We evaluated whether the Chinese literature on human genome epidemiology may offer insights on the operation of selective reporting and language biases.

METHODS AND FINDINGS

We targeted 13 gene-disease associations, each already assessed by meta-analyses, including at least 15 non-Chinese studies. We searched the Chinese Journal Full-Text Database for additional Chinese studies on the same topics. We identified 161 Chinese studies on 12 of these gene-disease associations; only 20 were PubMed-indexed (seven English full-text). Many studies (14-35 per topic) were available for six topics, covering diseases common in China. With one exception, the first Chinese study appeared with a time lag (2-21 y) after the first non-Chinese study on the topic. Chinese studies showed significantly more prominent genetic effects than non-Chinese studies, and 48% were statistically significant per se, despite their smaller sample size (median sample size 146 versus 268, p < 0.001). The largest genetic effects were often seen in PubMed-indexed Chinese studies (65% statistically significant per se). Non-Chinese studies of Asian-descent populations (27% significant per se) also tended to show somewhat more prominent genetic effects than studies of non-Asian descent (17% significant per se).

CONCLUSION

Our data provide evidence for the interplay of selective reporting and language biases in human genome epidemiology. These biases may not be limited to the Chinese literature and point to the need for a global, transparent, comprehensive outlook in molecular population genetics and epidemiologic studies in general.

ACE-DD genotype is associated with the occurrence of acute coronary syndrome in postmenopausal women

The insertion/deletion (I/D) polymorphism of the angiotensin converting enzyme (ACE), the A1166C polymorphism in the angiotensin type 1 receptor (AT1R), and the M235T polymorphism of the angiotensinogen gene are associated with cardiovascular disease mostly in men. Few data are available on the effects of these genetic variations in postmenopausal women according to hormone replacement therapy (HRT) use. In this case-control study, we determine the frequency of mutant alleles in the ACE I/D, M235T and A1166C polymorphisms in postmenopausal Caucasian women with and without a diagnosis of acute coronary syndrome (ACS). Data from 198 women with ACS (63+/-10 years) and 149 controls (62+/-7 years) showed that ACE-DD genotype was more prevalent in women with ACS compared to controls (30% vs. 19%, P<0.05). There was no difference in genotype distributions for either the M235T or the A1166C polymorphisms between groups. The difference in ACE genotype distribution between ACS women and controls was driven by current HRT users with 30% of ACS and 15% of controls carrying the ACE-DD genotype (P<0.05). The oligenic combination of ACE-DD and M235T-TT genotypes was higher in ACS compared to controls. Among carriers of M235T-TT, 7% of ACS and 1% of controls also had the ACE-DD genotype, P<0.05. Thus, the ACE-DD genotype may be associated with ACS in postmenopausal women, particularly in HRT users.

In an empirical evaluation of the funnel plot, researchers could not visually identify publication bias

BACKGROUND AND OBJECTIVE

Publication bias and related biases can lead to overly optimistic conclusions in systematic reviews. The funnel plot, which is frequently used to detect such biases, has not yet been subjected to empirical evaluation as a visual tool. We sought to determine whether researchers can correctly identify publication bias from visual inspection of funnel plots in typical-size systematic reviews.

METHODS

A questionnaire with funnel plots containing 10 studies each (the median number in medical meta-analyses) was completed by 41 medical researchers, including clinical research fellows in a meta-analysis class, faculty in clinical care research, and experienced systematic reviewers.

RESULTS

On average, participants correctly identified 52.5% (95% CI 50.6-54.4%) of the plots as being affected or unaffected by publication bias. The weighted mean percent correct, which adjusted for the fact that asymmetric plots are more likely to occur in the presence of publication bias, was also low (48.3 to 62.8%, depending on the presence or absence of publication bias and heterogeneous study effects).

CONCLUSION

Researchers who assess for publication bias using the funnel plot may be misled by its shape. Authors and readers of systematic reviews need to be aware of the limitations of the funnel plot.

The choice of a genetic model in the meta-analysis of molecular association studies

BACKGROUND

To evaluate gene-disease associations, genetic epidemiologists collect information on the disease risk in subjects with different genotypes (for a bi-allelic polymorphism: gg, Gg, GG). Meta-analyses of such studies usually reduce the problem to a single comparison, either by performing two separate pairwise comparisons or by assuming a specific underlying genetic model (recessive, co-dominant, dominant). A biological justification for the choice of the genetic model is seldom available.

METHODS

We present a genetic model-free approach, which does not assume that the underlying genetic model is known in advance but still makes use of the information available on all genotypes. The approach uses OR(GG), the odds ratio between the homozygous genotypes, to capture the magnitude of the genetic effect, and lambda, the heterozygote log odds ratio as a proportion of the homozygote log odds ratio, to capture the genetic mode of inheritance. The analysis assumes that the same unknown genetic model, i.e. the same lambda, applies in all studies, and this is investigated graphically. The approach is illustrated using five examples of published meta-analyses.

RESULTS

Analyses based on specific genetic models can produce misleading estimates of the odds ratios when an inappropriate model is assumed. The genetic model-free approach gives appropriately wider confidence intervals than genetic model-based analyses because it allows for uncertainty about the genetic model. In terms of assessment of model fit, it performs at least as well as a bivariate pairwise analysis in our examples.

CONCLUSIONS

The genetic model-free approach offers a unified approach that efficiently estimates the genetic effect and the underlying genetic model. A bivariate pairwise analysis should be used if the assumption of a common genetic model across studies is in doubt.

Genetic predictive factors in restenosis

Restenosis is still the main drawback of percutaneous transluminal coronary angioplasty (PTCA). It is thought to be a multifactorial process where recoil of the vessel, neointimal proliferation and thrombus formation are thought to play a role. Until now it has proven difficult to predict restenosis on clinical and procedural grounds, however, genetic epidemiology might provide more insights. In this review several genetic variables, i.e. polymorphisms that were determined in relation to restenosis are described. The single nucleotide polymorphisms (SNPs) described in the literature so far involve; the renin-angiotensin system, platelet aggregation, the inflammatory response, matrix metalloproteinases, smooth muscle cell proliferation, lipids and oxidative stress and nitric oxide. Nowadays DNA-microarrays have been developed which make it possible to test 50 or 60 polymorphisms at once. However, the risk of error due to multiple testing should be kept in mind. The results of the studies described should be interpreted with care. Many of the published studies are of relatively small sample size, which sometimes show more positive outcomes than the larger studies, this is possibly due to publication bias towards more positive results. The small sample size studies also exhibit wide confidence intervals. On the other hand, one must take into account that the process of restenosis is a multifactorial one and it is likely that multiple genes are involved. Thus, relatively small odds ratios relating to single gene contribution to restenosis can be of paramount importance when encompassed in the overall picture. Although still much research has to be done, stratification according to genetic make-up may enable tailoring of the interventional treatment to the individual patient.