Evaluating the context-dependent effect of family history of stroke in a genome scan for hypertension

Association of GSTT1 and GSTM1 gene polymorphisms with coronary artery disease in North Indian Punjabi population: a case-control study

BACKGROUND

Glutathione S-transferases are metabolic enzymes which are responsible for detoxification of endogenous (products of oxidative stress) as well as exogenous (drugs, pesticides, herbicides, environmental pollutants and carcinogens) products. Dysfunctional detoxification enzymes are responsible for the production of oxidative stress; a major contributor to the development of coronary artery disease (CAD).

OBJECTIVES

The present case-control study aimed to investigate the association of GSTT1 and GSTM1 gene polymorphisms with CAD.

METHODS

In the present study, 200 patients diagnosed with CAD and 200 age, sex and population subgroup matched healthy controls were enrolled. The GSTT1 and GSTM1 gene polymorphisms were examined using multiplex PCR.

RESULTS

The frequency of GSTT1 null genotype was significantly (p=0.038) lower in patients with CAD (6.00%) than in controls (12.50%). The GSTT1 null genotype showed protection against CAD (OR=0.45, 95% CI 0.22 to 0.92, p=0.028). The frequency of GSTM1 null genotype was significantly (p=0.004) higher in patients (31%) compared with controls (18%). The GSTM1 null genotype conferred twofold increased risk of developing CAD (OR=2.05, 95% CI 1.28 to 3.27, p=0.003).

CONCLUSIONS

The results concluded that the GSTT1 null genotype showed protection against CAD while the GSTM1 null genotype might be involved in the pathogenesis and development of CAD.

GSTM1, GSTT1, GSTP1, and GSTA1 genetic variants are not associated with coronary artery disease in Taiwan

BACKGROUND AND OBJECTIVE

The genetic variants of xenobiotic-metabolizing enzymes, such as those encoded by glutathione-S-transferase (GST) genes, may be associated with the risk of coronary artery disease (CAD). To investigate the genetic factors for CAD, we examined the GSTM1, GSTT1, GSTP1, and GSTA1 genotypes in a CAD cohort in Taiwan.

METHODS

Our study included 458 CAD participants and 209 control participants who received coronary angiography to assess CAD. The severity of CAD was defined as the number of coronary vessels with 50% or greater stenosis. Sequence variation of the GSTM1 and GSTT1 genes was determined using a polymerase chain reaction (PCR). The GSTP1 (Ile105Val), and GSTA1 (-69C>T) genetic variants were identified using a combination of PCR and restriction fragment length polymorphism analysis. Logistic regression analysis was used to calculate the odds ratios (ORs) and 95% confidence intervals.

RESULTS

Among the GST genetic variants examined, the GSTT1 null genotype was more prevalent in CAD participants with 3 stenosed vessels than in control participants (OR=1.64, P=.02). This association was no longer observed after adjusting for age, sex, smoking, alcohol use, diabetes mellitus, and serum levels of total cholesterol and high-density lipoprotein cholesterol (OR=1.28, P=.40). Both univariate and multivariate logistic regression analyses found no significant associations between CAD and the other genetic variants, either separately or in combination. In addition, no effects of interactions between the genotypes and environmental factors, such as cigarette smoking, were significantly associated with the risk of CAD.

CONCLUSION

The GST genetic variants examined were not associated with susceptibility to CAD in our Taiwanese cohort. This null association requires further confirmation with larger samples.

Genetic biomarkers of hypertension and future challenges integrating epigenomics

Essential hypertension is a multifactorial disease, considered to be one of the world's greatest public health problems. Despite recent, major, technical advances aiming to elucidate its genetic component, the discovered biomarkers up to now were reported to have only small effects, explaining consequently a tiny fraction of its phenotypic variance and resulting in a large proportion of missing heritability. Likewise, little evidence is available with regard to the epigenetic regulation of essential hypertension, since no robust biomarkers have yet been reported. In the current review, we discuss the main approaches used exclusively to study the genetics and epigenetics of essential hypertension, the biomarkers identified, their clinical utility and the difficulties to be overcome. Furthermore, we propose a new category of functional genetic-epigenetic biomarkers, eMethSNPs, and we provide their hypothetical gene expression profiles for a genetic functional regulation of hypertension via DNA methylation. Though believed to be infrequent, eMethSNPs could constitute a new category of mechanistically-based genetic biomarkers predisposing to essential hypertension.

Gene variants of the renin–angiotensin system and hypertension: from a trough of disillusionment to a welcome phase of enlightenment?

There is substantial evidence to suggest that BP (blood pressure) is an inherited trait. The introduction of gene technologies in the late 1980s generated a sharp phase of over-inflated prospects for polygenic traits such as hypertension. Not unexpectedly, the identification of the responsible loci in human populations has nevertheless proved to be a considerable challenge. Common variants of the RAS (renin–angiotensin system) genes, including of ACE (angiotensin-converting enzyme) and AGT (angiotensinogen) were some of the first shown to be associated with BP. Presently, ACE and AGT are the only gene variants with functional relevance, where linkage studies showing relationships with hypertension have been reproduced in some studies and where large population-based and prospective studies have demonstrated these genes to be predictors of hypertension or BP. Nevertheless, a lack of reproducibility in other linkage and association studies has generated scepticism that only a concerted effort to attempt to explain will rectify. Without these explanations, it is unlikely that this knowledge will translate into the clinical arena. In the present review, we show that many of the previous concerns in the field have been addressed, but we also argue that a considerable amount of careful thought is still required to achieve enlightenment with respect to the role of RAS genes in hypertension. We discuss whether the previously identified problems of poor study design have been completely addressed with regards to the impact of ACE and AGT genes on BP. In the context of RAS genes, we also question whether the significance of ‘incomplete penetrance’ through associated environmental, phenotypic or physiological effects has been duly accounted for; whether appropriate consideration has been given to epistatic interactions between genes; and whether future RAS gene studies should consider variation across the gene by evaluating ‘haplotypes’.

Appropriate Use of Information on Family History of Disease in Recruitment for Linkage Analysis Studies

When conducting genetic studies for complex traits, large samples are commonly required to detect any of the number of genes with relatively low effect thought to underly such traits. This is because, in contrast to monogenic diseases, complex traits typically result from a number of different genetic pathways (genetic heterogeneity) and any sample is likely to contain a considerable fraction of sporadic cases (phenocopies). Such samples are time-consuming and costly to recruit and analyse. Methods which might be used to decrease sample size include attempting to select families, with the aim of reducing genetic heterogeneity or phenocopy rate within the sample. Selecting cases with positive family history of disease should reduce the phenocopy rate, and this strategy has been employed in linkage studies of complex disease, although evaluations of such a strategy have been equivocal. This paper shows how identity by descent (IBD) distributions may be calculated for affected relative pairs recruited conditional on the affection status of a third relative. These distributions are then used to calculate expected power in affected sib and half-sib linkage studies when recruitment is conditional on family history of disease. We consider the proxy conditions of recruitment conditional on disease in an affected parent or third sibling with single-locus and additive multilocus genetic models. We show that while such selection strategies can reduce power if disease risk alleles are common and environmental heterogeneity low, under models more likely to underly common complex diseases power will generally be increased, and that this effect is greater as more loci are involved. Though the proxy cases studied are more extreme than a general strategy of asking potential recruits whether they have any family history of disease, these results suggest that conditional recruitment is more generally useful than previous studies have suggested.

Relevance of Genetics and Genomics for Prevention and Treatment of Cardiovascular Disease

Atherosclerotic cardiovascular disease (CVD) is a major health problem in the United States and around the world. Evidence accumulated over decades convincingly demonstrates that family history in a parent or a sibling is associated with atherosclerotic CVD, manifested as coronary heart disease, stroke, and/or peripheral arterial disease. Although there are several mendelian disorders that contribute to CVD, most common forms of CVD are believed to be multifactorial and to result from many genes, each with a relatively small effect working alone or in combination with modifier genes and/or environmental factors. The identification and the characterization of these genes and their modifiers would enhance prediction of CVD risk and improve prevention, treatment, and quality of care. This scientific statement describes the approaches researchers are using to advance understanding of the genetic basis of CVD and details the current state of knowledge regarding the genetics of myocardial infarction, atherosclerotic CVD, hypercholesterolemia, and hypertension. Current areas of interest and investigation--including gene-environment interaction, pharmacogenetics, and genetic counseling--are also discussed. The statement concludes with a list of specific recommendations intended to help incorporate usable knowledge into current clinical and public health practice, foster and guide future research, and prepare both researchers and practitioners for the changes likely to occur as molecular genetics moves from the laboratory to clinic.

Cardiovascular Genomics and Oxidative Stress

The majority of modifiable cardiovascular risk factors are complex, polygenic, or at least oligogenic traits, with genetic and environmental determinants playing important roles in disease risk and its phenotypic expression. The Human Genome Project and subsequent mouse and rat genome data have provided powerful tools to commence the dissection of genetic determinants of hypertension and other cardiovascular risk factors. Despite several new methodologies such as genome-wide scans, genome-wide gene expression profiling, and proteomic screens, it is fair to say that the progress of genetic studies designed as nonhypothesis driven has been relatively slow. On the other hand, several interesting candidate pathways have been identified, where investigators allowed for hypothesis-driven functional studies. One example of such pathway is vascular oxidative stress with its extensive network of genes and proteins, many with proven contributions to cardiovascular disease. Therefore, in parallel to genome-wide or proteome-wide studies, it will be constructive to pursue “pathwayomics” defined here as functional studies of a candidate pathway for disease pathogenesis.

Linkage of serum leptin levels in families with sleep apnea

OBJECTIVE

To identify regions on the genome linked to plasma leptin levels.

DESIGN

Full genome scan with 402 microsatellite markers, spaced approximately 10 cM apart. Data were analyzed using the Haseman-Elston regression linkage analysis.

SUBJECTS

A total of 160 sibling pairs from 59 predominantly African American, obese families recruited to participate in a genetic-epidemiological study of obstructive sleep apnea.

MEASUREMENTS

Serum leptin levels adjusted for age, sex, race and body mass index (BMI).

RESULTS

Suggestive linkage peaks were observed on chromosomes 2 (P=0.00170; marker D2S1384), 3 (P=0.00007; marker D3S3034), 4 (P=0.00020; marker D4S1652) and 21 (P=0.00053; marker D21s1411).

CONCLUSION

The peak on chromosome 3 is near the gene for glycogensynthase kinase 2 beta, an important factor in glucose homeostasis. Linkage was generally stronger after BMI adjustment, suggesting the potential influence of a number of metabolic pathways on leptin levels other than those that directly determine obesity levels. The evidence of linkage for leptin levels is consistent with prior linkage analyses for cholesterol, hypertension and other metabolic phenotypes.