Showing papers by "Nilesh J. Samani published in 1998"

Successful isolation of a rat chromosome 1 blood pressure quantitative trait locus in reciprocal congenic strains

Abstract: Linkage analyses in experimental crosses of hypertensive and normotensive rats have strongly suggested the presence of a quantitative trait locus (QTL) influencing blood pressure on rat chromosome 1, at or near the Sa gene. To confirm the presence of such a locus and move toward identification of the causative gene, we have developed, through targeted breeding over 10 generations using an Sa gene polymorphism to select breeders at each generation, 2 congenic strains, 1 containing a segment of spontaneously hypertensive rat (SHR) chromosome 1 in a Wistar-Kyoto rat (WKY) genetic background (WKY.SHR-Sa), and the other a segment of WKY chromosome 1 in an SHR background (SHR.WKY-Sa). WKY.SHR-Sa contains at least approximately 26 cM of SHR chromosome 1, between markers mD7mit206 and D1Mit2 (and including the SHR allele of the Sa gene), and SHR.WKY-Sa carries at least approximately 15 cM of WKY chromosome 1, between mD7mit206 and D1Wox34 (and including the WKY allele of the Sa gene). Blood pressure of WKY.SHR-Sa rats measured at 16, 20, and 25 weeks of age was significantly higher than that of WKY, whereas blood pressure of SHR.WKY-Sa rats was significantly lower than that of SHR. At 25 weeks, the mean differences in systolic and diastolic blood pressure between WKY.SHR-Sa and WKY were +11.5 mm Hg (P=0.001) and +11.6 mm Hg mm Hg (P<0.001), respectively. The corresponding differences between SHR.WKy-Sa and SHR were -11.3 mm Hg (P=0.002) and -9.1 mm Hg (P=0.005), respectively. The differences represent about one fifth of the blood pressure difference between SHR and WKY. Renal Sa mRNA levels in the congenic strains reflected their Sa allele with a high level in WKY. SHR-Sa and a low level in SHR.WKY-Sa, consistent with previous data suggesting that the level of Sa expression is primarily determined by cis-acting elements in or near the Sa gene. Our results show that we have successfully isolated a major rat chromosome 1 blood pressure QTL located in the vicinity of the Sa gene in reciprocal congenic strains derived from SHR and WKY. The strains can now be used to further define the region containing the QTL and also to characterize intermediary mechanisms through which the QTL influences blood pressure. In addition, comparison of the regions introgressed in our congenic strains with the location of the peak LOD score for chromosome 1 blood pressure QTL in second filial generation progeny derived from our SHRxWKY cross suggests that there may be at least 1 further QTL influencing blood pressure on this rat chromosome.

Distribution of Tissue Plasminogen Activator Insertion/Deletion Polymorphism in Myocardial Infarction and Control Subjects

Abstract: An insertion (I)/deletion (D) polymorphism in the tissue plasminogen activator (TPA) gene locus has recently been reported to be associated with the risk of myocardial infarction (MI) with increased risk in II/ID subjects compared with DD subjects. To investigate this further, we analysed 529 acute MI cases and 525 population-based control subjects recruited in two centers (Leicester and Sheffield, UK). We found no difference between cases and controls in TPA I/D allele frequencies (cases I = 0.574, controls I = 0.582, p = 0.74) or genotype distribution (cases II 33%, ID 48%, DD 19%; controls II 34%, ID 49%, DD 17%, p = 0.88). Compared with the DD genotype, the age, sex and centre adjusted odds ratios for MI for II genotype was 0.95 (95% confidence interval, 0.64-1.40, p = 0.85) and that for ID genotype was 0.89 (0.62-1.27, p = 0.56). There was no significant effect modification by smoking status, body mass index or cholesterol level. There was no difference in the reported frequency of positive family history of coronary heart disease or mean age at MI in the different genotype groups. We conclude that in our populations the TPA I/D polymorphism is not a major independent risk factor for myocardial infarction.

Differential regulation of ventricular adrenomedullin and atrial natriuretic peptide gene expression in pressure and volume overload in the rat

Abstract: 1. Adrenomedullin is a recently discovered vasodilating and natriuretic peptide whose physiological and pathophysiological roles remain to be established. Like atrial natiuretic peptide adrenomedullin is expressed in the left ventricle. Ventricular expression of atrial natriuretic peptide is known to be markedly increased by volume or pressure overload. In this study we investigated whether ventricular expression of adrenomedullin is similarly stimulated under such conditions. 2. Ventricular adrenomedullin and atrial natriuretic peptide mRNA levels as well as those of a loading control mRNA (glyceraldehyde-3-phosphate dehydrogenase) were quantified by Northern blot analysis in (a) rats with severe post-infarction heart failure induced by left coronary ligation at 30 days post-surgery and (b) in rats with pressure-related cardiac hypertrophy induced by aortic banding at several time points (0.5, 1 and 4 h, and 1, 4, 7 and 28 days) after surgery. Levels were compared with those in matched sham-operated controls. 3. The mRNA level of atrial natriuretic peptide was markedly increased (8–10-fold) in the left ventricle of animals with post-infarction heart failure. In contrast, there was only a modest (40%) increase in the level of adrenomedullin mRNA. In rats with pressure-induced cardiac hypertrophy the ventricular level of atrial natriuretic peptide mRNA was again markedly increased (maximum 10-fold). The increase was first noticeable at 24 h post-banding and persisted until 28 days. In contrast, there was no change in adrenomedullin mRNA level compared with sham-operated rats at any time point. 4. Despite having similar systemic effects, the expression of adrenomedullin and atrial natriuretic peptide in the left ventricle is differently regulated. The findings imply distinct roles for the two peptides. The results do not support an important role for ventricular adrenomedullin expression in the remodelling process that occurs during the development of cardiac hypertrophy but suggest that ventricular adrenomedullin participates in the local and/or systemic response to heart failure

Molecular genetics of coronary artery disease: measuring the phenotype.

Abstract: Conventional risk factors explain only about half the risk of coronary artery disease (CAD) [1]. The strong familial predisposition to CAD [2], combined with advances in DNA analysis, has led to a proliferation of studies in recent years attempting to identify genetic factors that influence risk. The approach taken by most studies has been to examine the association of naturally occurring genetic variation (polymorphisms) in candidate genes with risk of or severity of CAD. Given the complex pathophysiology of coronary atherosclerosis and the processes that lead to the clinical syndromes [3], there is no lack of candidate genes worthy of study. In this issue of Clinical Science, two studies examine the role of variation in the gene for transforming growth factor-β1 (TGF-β1). TGF-β1 is a cytokine with several functions which could both inhibit and advance the development and progression of atherosclerosis. However, in 655 patients with CAD confirmed angiographically and 244 angiographically normal individuals, Syrris et al. [4] found no association of five different polymorphisms in the gene with CAD. Haplotypes constructed from linkage of individual polymorphisms also did not associate with CAD. Wang et al. [5], on the other hand, examined whether a polymorphism (C509T) in the promoter region of the gene, one of those also studied by Syrris et al. [4], influenced the severity of coronary disease, as judged by the number of significantly diseased vessels at angiography in 371 patients. Once again, no association was found of the polymorphism with this phenotype, or indeed with a prior history of myocardial infarction in the cohort. In addtion, the polymorphism did not have any discernible effect on the circulating level of TGF-β1. This is of particular relevance as circulating TGF-β1 levels have been found to be altered in subjects with severe coronary disease, although the data are conflicting with both depressed [6] and elevated [7] levels being reported. Association studies examine the role of individual polymorphisms and, by inference, any variations that are in significant linkage disequilibrium. However, when negative as in the studies of Syrris et al. and Wang et al., they cannot exclude an effect of a gene locus. Construction of haplotypes as done by Syrris et al. brings association studies closer to the type of locus exclusion permitted by linkage analysis, although in this case the study was probably underpowered to do this adequately. Thus it remains possible that other variations at the TGFβ1 locus still play a role in the pathogenesis of CAD. However, the two studies usefully serve to highlight a more general dilemma facing researchers in this area, namely which CAD phenotype to look at and how best to measure it. Because of both clinical relevance and patient access, two CAD phenotypes have been most commonly studied – myocardial infarction and angiographically documented coronary disease. Myocardial infarction has the great advantage of having well-defined criteria for diagnosis. An important consequence of this is that it is also relatively easy to identify controls who have not suffered an event, although as the condition can occur without any prior symptoms, and is an ageand gender-dependent process, it is important that controls are well matched for these criteria, in addition to others such as ethnicity which can impact on allele frequencies. The other major advantage of myocardial infarction as a phenotype is that in most cases it can be fairly accurately timed. This means that, in addition to any overall association, one can also examine whether an allele or genotype is associated more strongly with myocardial infarction in younger subjects or with a younger mean age at time of myocardial infarction, features one may expect of a risk factor. The main disadvantage of studying myocardial infarction is the unavoidable loss of subjects through fatality when subjects are recruited after the incident event, even if this is done in admission wards or coronary care units, as more than half the acute deaths occur before subjects even reach hospitals. This could become of paramount importance if a genetic factor, unknowingly, also influences survival after myocardial infarction. This is of course the major reason why findings from prospective studies carry extra weight. Use of the presence of coronary disease documented angiographically as a phenotype poses different problems. First, it is a chronic process and the onset is difficult to define. Secondly, although angiography is useful in identifying the presence of haemodynamically significant coronary stenoses (often defined as stenoses " 50%). it is an insensitive technique for quantifying the extent of atheroma. Patterns vary from focal lesions to diffuse involvement of large segments of vessels. Indeed, an interesting but unresolved question is whether different biological processes influence the pattern of coronary atheroma deposition. Furthermore, recent studies using intravascular coronary ultrasound [8,9] have shown that considerable atheroma may already exist in even angiographically ‘normal ’ coronary segments due to extrinsically directed remodelling [10]. Therefore, classification of severity of coronary disease simply on the basis of the

Genetic analysis of the SA and Na+/K+-ATPase alpha1 genes in the Milan hypertensive rat.

Abstract: Objective To study whether the S A gene locus (on rat chromosome 1) and the sodium potassium ATPase α 1 gene locus (on rat chromosome 2) contribute to the elevated blood pressure in the Milan hypertensive rat. Design Co-segregation analysis using polymorphisms in the S A and Na + /K + -ATPase α 1 genes in F 2 rats from a cross of Milan hypertensive and Milan normotensive rats. Analysis of S A and N + /K + -ATPase α 1 gene expression in kidneys of 6 and 25 weeks old Milan hypertensive and normotensive rats. Methods Genotyping of F 2 rat DNA by restriction digestion and Southern blotting and comparison of messenger RNA levels by northern blot analysis. Results Renal expression of S A was considerably higher in normotensive than it was in hypertensive rats aged 6 and 25 weeks. Despite this difference the S A genotype did not co-segregate with blood pressure, although the Milan hypertensive rat allele did co-segregate with greater body weight (P= 0.0014) for male F 2 rats. Expression of Na + /K + -ATPase σ 1 was higher in the kidneys of young hypertensive rats than it was in those of normotensive rats and did not decline with age as occurred in the normotensive rats. However, again the Na + /K + -ATPase α 1 genotype did not co-segregate with blood pressure. Conclusions Despite differences in the patterns of expression of S A and Na + /K + -ATPase α 1 genes in the kidneys of Milan hypertensive and normotensive rats, we found no evidence of co-segregation of either gene with blood pressure. Our results suggest that either S A is simply acting as marker for a linked gene in other crosses for which co-segregation with blood pressure has been observed, or at least, the level of its renal expression is not the sole determinant of its effect on blood pressure. The failure of the Na + /K + -ATPase α 1 gene to co-segregate with blood pressure suggests that its greater expression in the kidney of the Milan hypertensive rat is either reactive or controlled by other genetic loci.

Methylenetetrahydrofolate reductase mutation and coronary artery disease.

Abstract: To the Editor: The article by Kluijtmans and colleagues1 ( Circulation , October 21, 1997) adds to the growing literature on the relationship between the common thermolabile variant of methylenetetrahydrofolate reductase (MTHFR) and risk of vascular disease. In an angiographically assessed cohort of subjects with coronary artery disease (CAD) participating in a statin regression trial (REGRESS), significantly increased homocysteine concentrations were found in subjects homozygous (+/+) or heterozygous (+/−) for the thermolabile variant compared with those carrying only the normal variant (−/−). Median levels were 2.8 and 0.8 μmol/L higher in the +/+ and +/− subjects, respectively. Compared with population-based controls, there was trend toward higher risk of CAD in subjects carrying the thermolabile variant, but this did not reach significance (OR for +/+ versus −/−: 1.21 [0.87 to 1.68]; +/− versus −/−: 1.14 [0.94 to 1.38]). However, when the results were combined with those of 6 other studies, including our own,2 in a meta-analysis, there was a significant increase in relative risk in subjects with the +/+ genotype (OR, …

A positive parental history of high blood pressure

Abstract: Familial aggregation of blood pressure (BP) has been recognised for a long time and enquiry about family history, especially in parents, forms a standard part of our assessment of a hypertensive patient. To some extent, a positive response conditions our interpretation of the patient’s BP and also provides a simple (although not necessarily true) explanation for the patient’s condition that he/she can easily understand—‘it runs in your genes’! How strong is the influence of a positive family history of hypertension? Two approaches have been used to analyse this. First, studies have looked at the effect of a family history on the risk of developing hypertension. The most comprehensive analysis has been done by Hunt and colleagues in Utah. In a prospective study of 1482 adults, a positive family history (two first-degree relatives with hypertension) was associated with a 2.35-fold unadjusted and a 1.82-fold adjusted risk of hypertension. In a separate study of 94 292 persons, they investigated parameters that influenced this familial risk. Age of subject, number of affected relatives and the ages at which they developed hypertension all had significant effects. Risk was highest (4.1-fold for males, 5.0-fold for females) in young adults (20–39 years) when both parents were affected early (,55 years of age). The risk associated with a positive family history decreased rapidly and was not at all apparent, even with a strong family history, in subjects over the age of 60. The alternative approach has been to directly quantify the effect of a positive family history on BP. Again several studies have shown that subjects with a positive history (variously defined) have higher BP than those without such a history. This is true for both clinic as well as ambulatory BP with group differences of between 3 and 13 mm Hg for systolic BP. Most of these studies have focused on relatively young subjects (,35 years) because of the view that familial factors are likely to act early. In this issue of the Journal of Human Hypertension Naruse et al