Self-rated health scores predict mortality among people with type 2 diabetes differently across three different country groupings: findings from the ADVANCE and ADVANCE-ON trials

AIMS

To explore whether there is a different strength of association between self-rated health and all-cause mortality in people with type 2 diabetes across three country groupings: nine countries grouped together as 'established market economies'; Asia; and Eastern Europe.

METHODS

The ADVANCE trial and its post-trial follow-up were used in this study, which included 11 140 people with type 2 diabetes from 20 countries, with a median follow-up of 9.9 years. Self-rated health was reported on a 0-100 visual analogue scale. Cox proportional hazard models were fitted to estimate the relationship between the visual analogue scale score and all-cause mortality, controlling for a range of demographic and clinical risk factors. Interaction terms were used to assess whether the association between the visual analogue scale score and mortality varied across country groupings.

RESULTS

The visual analogue scale score had different strengths of association with mortality in the three country groupings. A 10-point increase in visual analogue scale score was associated with a 15% (95% CI 12-18) lower mortality hazard in the established market economies, a 25% (95% CI 21-28) lower hazard in Asia, and an 8% (95% CI 3-13) lower hazard in Eastern Europe.

CONCLUSIONS

Self-rated health appears to predict 10-year all-cause mortality for people with type 2 diabetes worldwide, but this relationship varies across groups of countries.

Involvement of human monogenic cardiomyopathy genes in experimental polygenic cardiac hypertrophy

Hypertrophic cardiomyopathy thickens heart muscles, reducing functionality and increasing risk of cardiac disease and morbidity. Genetic factors are involved, but their contribution is poorly understood. We used the hypertrophic heart rat (HHR), a unique normotensive polygenic model of cardiac hypertrophy and heart failure, to investigate the role of genes associated with monogenic human cardiomyopathy. We selected 42 genes involved in monogenic human cardiomyopathies to study: 1) DNA variants, by sequencing the whole genome of 13-wk-old HHR and age-matched normal heart rat (NHR), its genetic control strain; 2) mRNA expression, by targeted RNA-sequencing in left ventricles of HHR and NHR at 5 ages (2 days old and 4, 13, 33, and 50 wk old) compared with human idiopathic dilated cardiomyopathy data; and 3) microRNA expression, with rat microRNA microarrays in left ventricles of 2-day-old HHR and age-matched NHR. We also investigated experimentally validated microRNA-mRNA interactions. Whole-genome sequencing revealed unique variants mostly located in noncoding regions of HHR and NHR. We found 29 genes differentially expressed in at least 1 age. Genes encoding desmoglein 2 ( Dsg2) and transthyretin ( Ttr) were significantly differentially expressed at all ages in the HHR, but only Ttr was also differentially expressed in human idiopathic cardiomyopathy. Lastly, only two microRNAs differentially expressed in the HHR were present in our comparison of validated microRNA-mRNA interactions. These two microRNAs interact with five of the genes studied. Our study shows that genes involved in monogenic forms of human cardiomyopathies may also influence polygenic forms of the disease.

Fine mapping of Lvm1: a quantitative trait locus controlling heart size independently of blood pressure

We have previously reported a quantitative trait locus (QTL) on rat chromosome 2 that influences heart size independently of blood pressure (Left Ventricular Mass Locus 1; Lvm1). The recent release of the rat genome sequence allowed us to retest and refine this relatively broad QTL with a view to identifying within it candidate genes worthy of structural investigation. We sought to achieve this 'fine mapping' by increasing the marker density within the interval and undertaking a linkage analysis in a previously defined population of F2 hybrids generated from inbred spontaneously hypertensive rats (SHR) of the Okamoto strain and Fischer rat (F344) progenitors. We were able to reconfirm and resolve Lvm1 from its original width of approximately 45 to 15 cM. By reference to the ENSEBL rat genome data bank, we identified within Lvm1 27 known genes, 109 predicted genes and 7 pseudogenes. Of the known genes, candidates include potential regulators of cardiac growth, a sodium channel and calcium channel as well as the fibroblast growth factor 2 gene. Located nearby the Lvm1 locus was the gene for the angiotensin Type 1B receptor. Given the evidence that the ligand for the angiotensin Type 1B receptor-angiotensin II-is a potent cardiotroph, we also consider this gene a potential candidate. The identification of the precise allelic variant(s) within Lvm1 involved in the control of pressure-independent cardiac growth awaits further molecular studies.

Sex, genes and blood pressure

1. Throughout most of life, males have higher average blood pressures than females. This sexual dichotomy may be related to genetic factors including the X and Y sex chromosomes and genes that control sex steroids. Resultant physiological differences between men and women may also be relevant to the quantitative variation of blood pressure within the sexes. 2. The present overview collates our published and novel sex-related genetic data in relation to blood pressure from the Victorian Family Heart Study. These include a multipoint quantitative linkage analysis of the X chromosome and genetic association studies of single nucleotide polymorphisms (SNP) of the Y chromosome and genes encoding the androgen receptor (AR), oestrogen receptor alpha (ERalpha), 5alpha-reductase types I and II (SRD5A1 and SRD5A2) and aromatase (CYP19). 3. Systolic blood pressure (SBP) was linked (Z=3.3, genome-wide P < 0.05) to a region of the X chromosome that encompassed the AR gene and the Y chromosome was associated with diastolic blood pressure (DBP; P=0.03). In new analyses, we observed a possible association between a SNP in AR and DBP in 369 males (84.5 vs 82.1 mmHg for genotype A vs genotype B, respectively; P=0.06) and a significant association between haplotypes of the Y chromosome and AR SNP in males (P=0.01) with a difference of nearly 6 mmHg DBP between extreme groups. Associations were also observed for polymorphisms of SRD5A1 and ERalpha with DBP and SBP in males, respectively. 4. The findings indicate that genes related to sexual phenotypes may be relevant to the normal variation in blood pressure, even within the sexes. Further genetic and physiological analyses will be required to confirm these observations and to determine the mechanisms of action and the nature of any interactions.

Significant population variation in adult male height associated with the Y chromosome and the aromatase gene

The determination of human adult height is dependent on both environmental and genetic factors. Rare causes of abnormal stature have been identified, including mutations in the gene encoding aromatase (CYP19) and regions on the Y chromosome. However, the possible role of these loci in the genetic control of normal adult height is unknown. We have performed an association study using common biallelic polymorphisms within CYP19 and the Y chromosome to determine whether these loci are associated with variation in height in 413 adult males and 335 females drawn at random from a large population sample. An association between CYP19 and height was found (difference, 2.0 cm; 95% confidence interval, 0.16-3.8; P = 0.003), but this was more evident in men (difference, 2.3 cm; 95% confidence interval, 0.38-4.4; P = 0.05) than women (difference, 0.2 cm; 95% confidence interval, -2.1 to 1.6; P = 0.94). An association was also found with the Y chromosome (P = 0.009; difference of 1.9 cm; 95% confidence interval, 0.5-3.4). Additionally, when men were grouped according to haplotypes of the CYP19 and Y chromosome polymorphisms, a difference of 4.2 cm (95% confidence interval, 0.67-7.3) was detected (P = 0.004). These results suggest that in men, genetic variation in CYP19 and on the Y chromosome are involved in determining normal adult height, and that these loci may interact in an additive fashion.

Physiological relationships between central vascular haemodynamics and left ventricular structure

Left ventricular hypertrophy is an independent cardiovascular risk factor. In hypertensives, the pattern of hypertrophy is influenced by central haemodynamic characteristics. Central haemodynamics may also determine physiological differences in left ventricular structure and predispose to particular responses of the left ventricle to pathological increases in load. M-mode echocardiography was used to measure left ventricular diastolic dimension and to estimate left ventricular mass index, relative wall thickness and stroke volume in 159 healthy volunteers aged between 19 and 74 years. Tonometric sphygmography was used to estimate augmentation index, central end-systolic and mean arterial blood pressure. Effective arterial elastance was calculated as the ratio of end-systolic pressure to stroke volume. Left ventricular mass index and relative wall thickness were adjusted for variation in age, sex and blood pressure before analyses. Left ventricular diastolic dimension exhibited significant inverse correlations with both effective arterial elastance (r=-0.72, P<0.0001) and augmentation index (r=-0.23, P=0.004). Adjusted left ventricular mass index was inversely correlated with effective arterial elastance (r=-0.35, P<0.0001), but no correlation was observed between left ventricular mass index and augmentation index (r=0.04). Adjusted relative wall thickness correlated with increasing effective arterial elastance (r=0.32, P<0.0001) and augmentation index (r=0.18, P=0.02). Relative wall thickness (r=0.34, P<0.0001), but not left ventricular mass index, correlated with age. Higher elastance and augmentation correlates with relatively smaller left ventricular cavity size but larger relative wall thickness. Age-related changes in left ventricular afterload may affect relative wall thickness more significantly than left ventricular mass index and may contribute to a particular change in left ventricular geometry with age.

Male pattern baldness is not associated with established cardiovascular risk factors in the general population

A number of studies have shown an association between male pattern baldness (MPB) and cardiovascular disease. Few of these studies, however, have examined whether MPB is a novel risk factor, or is associated with abnormalities of established coronary risk factors. We have therefore performed an analysis of MPB and cardiovascular risk factors in the general population. A total of 1219 male participants aged 18-70 years from the Victorian Family Heart Study were surveyed using a validated questionnaire for degree and pattern of baldness. Carefully standardized measures of height, weight, blood pressure, pulse rate, total and high-density lipoprotein cholesterol, and plasma fibrinogen were made. Subjects were grouped according to the degree and pattern of baldness as: no baldness, frontal baldness and vertex baldness. Bald men were older than non-bald men (P < 0.0001). Age was also associated with increased levels of coronary risk factors (P < 0.0001). When multiple regression was used to adjust for age differences, the levels of coronary risk factors were not significantly different between the bald and non-bald groups. The lack of association between baldness and established coronary risk factors implies that baldness may predispose to coronary heart disease through novel mechanisms yet to be defined.

Polymorphism of the androgen receptor gene is associated with male pattern baldness

The common heritable loss of scalp hair known as male pattern baldness or androgenetic alopecia affects up to 80% of males by age 80. A balding scalp is characterized by high levels of the potent androgen dihydrotestosterone and increased expression of the androgen receptor gene. To determine if the androgen receptor gene is associated with male pattern baldness, we compared allele frequencies of the androgen receptor gene polymorphisms (StuI restriction fragment length polymorphism and two triplet repeat polymorphisms) in cases with cosmetically significant baldness (54 young and 392 older men) and controls (107 older men) with no indication of baldness. The androgen receptor gene StuI restriction site was found in all but one (98.1%) of the 54 young bald men (p = 0.0005) and in 92.3% of older balding men (p = 0.000004) but in only 76.6% of nonbald men. The combination of shorter CAG and GGC triplet repeat lengths was also more prevalent in bald men (p = 0.03). The ubiquity of the androgen receptor gene StuI restriction site, and higher incidence of shorter triplet repeat haplotypes in bald men suggests that these markers are very close to a functional variant that is a necessary component of the polygenic determination of male pattern baldness. Functional mutation in or near the androgen receptor gene may explain the reported high levels of expression of this gene in the balding scalp.

Association of the human Y chromosome with high blood pressure in the general population

Genetic variation in the Y chromosome has significant effects on male blood pressure in experimental animals, but the effects in humans are unknown. We examined the relationship between blood pressure and a polymorphic HINdIII restriction site in the nonrecombining region of the Y chromosome in 409 randomly selected men from the general population. Carefully standardized measures of systolic and diastolic blood pressures were made. The HINdIII restriction site was significantly more common (43.2%) in men in the lowest decile of the diastolic blood pressure distribution than men in the highest decile (15.9%, P=0.007). No significant difference in genotype frequency was observed between the lowest and highest deciles for systolic pressure (32.4% versus 27.8%, P=0.66). In the entire group, men with the HIN:dIII restriction site had significantly lower diastolic blood pressures (81.2 mm Hg, SD:8.3, versus 83.2 mm Hg, SD:8.7, P=0.03). No significant differences in systolic blood pressure (130.6 mm Hg, SD:14.7, versus 128.3 mm Hg, SD:13.6) were observed in relation to genotypes. Our results indicate that genetic variation in the human Y chromosome is associated with high blood pressure and contributes significantly to the quantitative variation of male diastolic blood pressure in the general population.

Familial patterns of covariation for cardiovascular risk factors in adults: The Victorian Family Heart Study

The Victorian Family Heart Study was established to address the causes of familial patterns in cardiovascular risk factors. From 1990 to 1996, a representative population sample of 783 adult families (2,959 individuals), each comprising both parents (40-70 years) and at least one natural adult offspring (18-30 years), was recruited in Melbourne, Australia. Included in both generations were 461 monozygotic and dizygotic twins as pairs or singletons. A multivariate normal model was used for pedigree analysis of height, weight, body mass index, diastolic and systolic blood pressure, pulse rate, and total and high density lipoprotein cholesterol. All traits showed evidence for additive genetic variation, explaining from 55% (height) to 26% (pulse) of age- and sex-adjusted variance. An effect persisting into adulthood of shared family environment during cohabitation explained from 39% (body mass index) to 13% (systolic blood pressure) of variance (not nominally significant for diastolic blood pressure). These shared environmental effects were strongest within twin pairs, less so for sibling pairs, and least for parent-offspring pairs (in which an effect was not observed for weight, diastolic and systolic blood pressure, and total cholesterol). On a background of genetic influences, there are periods in early life during which the family environment cements long-term correlations between adult relatives in cardiovascular risk factors.

Increased left ventricular mass is not associated with impaired left ventricular diastolic filling in normal individuals

BACKGROUND

Hypertensive left ventricular (LV) hypertrophy has been associated with diastolic dysfunction. However, the underlying physiological relationship between LV size and diastolic function remains to be clarified. The aim of this study was to evaluate the relationship between several measures of diastolic filling and LV mass in a population sample.

METHODS

We used M-mode and Doppler echocardiography to compare left ventricular mass index (LVMI) and wall thickness with five measures of ventricular diastolic filling (ratio of the peak early mitral inflow velocity to the peak atrial mitral inflow velocity, deceleration time of early mitral inflow, isovolumetric relaxation time, ratio of the peak pulmonary venous systolic to diastolic flow and difference between the durations of the pulmonary venous and mitral inflow atrial waves) in 159 healthy volunteers.

RESULTS

LVMI was significantly (P< 0.0001) greater in men (81.3 g/m2, interquartile range: 67-94) than women (59.7 g/m2, interquartile range: 49-74), but no gender differences were observed in diastolic filling. Higher age, blood pressure and heart rate showed significant correlation with diminished diastolic filling. However, no measure of diastolic filling correlated with LVMI or wall thickness in either univariate or multiple regression analyses that adjusted for relevant covariates.

CONCLUSIONS

LVMI does not explain physiological differences in diastolic filling. The significant decline in diastolic filling with age reflects changes in the quality rather than the quantity of myocardial tissue.

Cardiovascular disease: genes and public health

INTRODUCTION

The advances in molecular biology hold great promise for complex conditions such as cardiovascular disease. Early accurate diagnosis and new preventive and treatment strategies are among the potential benefits of genetic understanding. Many genes and mutations have been discovered that contribute to rare Mendelian forms of cardiovascular disease. However, there has been little tangible success in defining specific mutations that explain the more common forms of cardiovascular disease. Of the numerous genes tested, inconsistent results are a recurring theme.

METHODS

This review addresses broader issues that touch on the clinical and epidemiological context in which the genetics of cardiovascular disease might develop. How do genes and environment interact in cardiovascular disease? What characteristics of a marker might make it useful? How will genetic understanding be used? What is the place of physiology in molecular biology? Is the future of genetics in patient management or public health?

RESULTS

It is concluded that individuals and communities are unlikely to accept widespread DNA screening, and less likely to tolerate genetic manipulation. Genetic complexity will make the identification of specific mutations an expensive and potentially thankless task.

CONCLUSIONS

Genetics may reveal new pathophysiological mechanisms against which simple, safe and effective public health measures can bring benefit to the greatest number.

Glomerular hyperfiltration, high renin, and low- extracellular volume in high blood pressure

Abnormal renovascular resistance and glomerular filtration rate are characteristic of established hypertension and may also be involved in its pathogenesis. To determine renal and body fluid correlates of the predisposition to high blood pressure, we examined 100 healthy young adults with high or low blood pressure. Within each group, half had parents with high blood pressures, and half had parents with low blood pressures. Renal function and hemodynamics, body fluid volumes, and relevant hormones and genotypes were measured. Subjects with high personal and parental blood pressures had the highest levels of glomerular filtration rate (P<0.02) and plasma active renin concentration and low levels of exchangeable sodium and plasma volume (P<0.02). High glomerular filtration rate was not associated with differences in urinary kallikrein or prostaglandins. Polymorphisms of the renin, angiotensin-converting enzyme, and angiotensinogen genes were not associated with differences in glomerular filtration rate or renin. Subjects with high personal, but low parental, blood pressures had low exchangeable sodium and plasma volumes (P<0.02) but normal glomerular filtration rates. In this population, extracellular volume depletion and high renin are correlates of high blood pressure in early adulthood, and glomerular hyperfiltration is a feature of those who also have familial predisposition to high blood pressure.

New target regions for human hypertension via comparative genomics

Models of human disease have long been used to understand the basic pathophysiology of disease and to facilitate the discovery of new therapeutics. However, as long as models have been used there have been debates about the utility of these models and their ability to mimic clinical disease at the phenotypic level. The application of genetic studies to both humans and model systems allows for a new paradigm, whereby a novel comparative genomics strategy combined with phenotypic correlates can be used to bridge between clinical relevance and model utility. This study presents a comparative genomic map for "candidate hypertension loci in humans" based on translating QTLs between rat and human, predicting 26 chromosomal regions in the human genome that are very likely to harbor hypertension genes. The predictive power appears robust, as several of these regions have also been implicated in mouse, suggesting that these regions represent primary targets for the development of SNPs for linkage disequilibrium testing in humans and/or provide a means to select specific models for additional functional studies and the development of new therapeutics.

Linkage analysis of endothelial nitric oxide synthase gene with human blood pressure

OBJECTIVE

Endothelial nitric oxide exerts important effects on the regulation of vascular tone and structure. Variants of the endothelial nitric oxide synthase gene (eNOS) have been associated with hypertension and myocardial infarction, although some reports have shown negative linkage with hypertension. To examine whether the region encoding the eNOS gene is linked with physiological blood pressure variation, we undertook a linkage analysis of this region in the general population.

DESIGN

In healthy volunteer families, we used two independent quantitative linkage analyses to examine the relationship between genotypes and phenotypes, with both parametric and non-parametric and single-locus and multi-point methods.

METHODS

We selected 260 families comprising mother and father (aged 40-70 years) and two natural offspring (aged 18-30 years) from the Victorian Family Heart Study. After standardized measurement of clinical data and extraction of DNA, all family members were genotyped at five microsatellite loci including the CA repeat in the eNOS gene by a PCR method. The quantitative linkage analyses were conducted according to two different analysis programs, the Genetic Analysis System (GAS) and the MAPMAKER/SIBS.

RESULTS

With both linkage analyses, we found no linkage between any of the loci on chromosome 7q35-36 and the phenotypes systolic and diastolic blood pressure, mean arterial pressure, pulse pressure, pulse rate, weight, height and body mass index.

CONCLUSION

Based on these results, we conclude that in this population the eNOS gene is not linked to the physiological variation of blood pressure and other related phenotypes.

Discrepancies between echocardiographic measurements of left ventricular mass in a healthy adult population

Increased left ventricular (LV) mass is associated with increased cardiovascular morbidity and mortality. LV mass is commonly estimated from echocardiography according to the Penn or ASE (American Society of Echocardiography) conventions. No formal statistical test of agreement between these methods has been published. Therefore we compared M-mode echocardiographic LV mass estimates by the Penn and ASE methods in a normal adult population. M-mode echocardiographic tracings were obtained in 169 healthy volunteers and used to calculate LV mass using the Penn and ASE methods. Median values of the estimates were similar [Penn, 126 g (interquartile range 96-170 g); ASE, 129 g (105-164 g); P=0.08] and were highly intercorrelated (r=0.98, P<0.0001). However, the Bland-Altman analysis of agreement revealed significant inconsistencies between Penn and ASE LV mass values. The difference between Penn and ASE values was correlated significantly with heart size (P<0.0001), such that, for small hearts, the Penn LV mass was lower than the ASE LV mass; in contrast, for large hearts, Penn estimates were greater than ASE values. In the upper 5% of the LV mass distribution, the median value for the Penn LV mass index was 132.4 g/m(2), compared with 116.5 g/m(2) for ASE values (2P=0.017). Thus the two most common methods of echocardiographic estimation of LV mass differ significantly at the upper and lower ends of the heart size distribution. These results have important implications for both cardiac research and clinical evaluation.

Insulin gene polymorphism and premature male pattern baldness in the general population

Insulin is found in hair follicles and may play a role in the regulation of androgen metabolism and the hair growth cycle, which are relevant to the loss of scalp hair known as male pattern baldness. An excess of dihydrotestosterone on balding scalp indicates that the condition is androgen dependent. Premature male pattern baldness may be the male phenotype of familial polycystic ovary syndrome, a condition characterized by high levels of androgens and insulin that has been linked to insulin gene polymorphism. Therefore, we studied possible associations between relevant insulin gene polymorphisms and premature male pattern baldness in the general community. We examined the distribution of three dimorphic restriction fragment length polymorphisms: HphI, PstI and FokI in cases consisting of 56 men aged 18-30 years with significant baldness, and in 107 control men aged 50 years or more with no indication of baldness. No significant differences between cases and controls in allele, genotype or haplotype frequencies were identified. We conclude that, in the general population, the insulin gene is not associated with premature male pattern baldness.

The new asthma genetics and its implications for public health

OBJECTIVE

To review the genetics of asthma from a public health perspective.

DATA SOURCES

Studies of asthma genetics published between 1990 and 1997 were reviewed.

STUDY SELECTION

Studies based on random population sampling were preferred. Both linkage and association studies were included, as were genome scans. Studies needed to report results for asthma or the related traits of atopy and bronchial hyperreactivity (BHR).

DATA EXTRACTION

The chromosomal locations linked to or candidate genes associated with asthmatic traits were tabulated.

DATA SYNTHESIS

A clear majority of studies relied on clinical ascertainment or highly inbred populations. Although there is no consensus about the definition of asthma, phenotypic characterisation of subjects is more complete in recent studies. The high affinity IgE receptor gene on chromosome 11q and a cluster of cytokine genes on chromosome 5q are linked both to atopy and BHR. The T cell receptor gene on chromosome 14q is linked to specific IgE responses, and a region on chromosome 12q is linked both to total IgE levels and asthma. Genome scans have identified other regions of interest on chromosomes 2q, 4, 5p, 6, 7, 11p, 13, 16, 17, 19q, and 21q.

CONCLUSIONS

Asthma is a complex polygenic disorder with marked gene-environment interactions. However, it is proving tractable to powerful new genetic approaches arising from the human genome project. At the present state of knowledge, population screening for the asthma genes so far identified cannot be justified. Gene therapy for asthma is an even more remote prospect.

Long-term effects of angiotensin-converting enzyme inhibition on renal medullary neutral lipid in spontaneously hypertensive rats

Short-term treatment of young spontaneously hypertensive rats (SHR) with angiotensin-converting enzyme (ACE) inhibitors reduces systolic blood pressure. Renal medullary neutral lipids (RMNLs) have vasodilator properties that may explain the effects of ACE inhibition. We measured RMNL levels of SHR treated between 6 and 10 weeks of age with (1) vehicle, (2) ramipril 1 mg. kg-1. d-1, (3) the bradykinin B2 receptor antagonist icatibant 0.5 mg. kg-1. d-1, or (4) icatibant 0.5 mg. kg-1. d-1 plus ramipril 1 mg. kg-1. d-1. RMNLs were quantified by oil red O fluorescence at 10 and 20 weeks of age. Systolic blood pressure (BP) was measured by tail-cuff plethysmography. Ramipril reduced BP at 10 weeks of age and increased RMNLs compared with controls (0.99+/-0.07% versus 0.56+/-0. 06%, P<0.01). Icatibant alone had no significant effect on RMNLs (0.55+/-0.04%) but attenuated the increase in RMNLs by ramipril (0. 81+/-0.05%). In control SHR, the increase in BP between 10 and 20 weeks of age was associated with a significant increase in RMNLs (0.79+/-0.09%). SHR that had received ramipril had significantly lower BP than controls at 20 weeks of age, but RMNL was not significantly different (0.92+/-0.10%). Therefore, in young SHR, ACE inhibition increases RMNLs and reduces blood pressure, an effect that appears to depend on bradykinin. The changes in RMNLs at the age of 10 weeks paralleled long-term BP effects and may be involved in setting the BP track in SHR.

Mutational analysis of the high affinity immunoglobulin E receptor beta subunit gene in asthma

BACKGROUND

The gene for the beta subunit of the high affinity receptor for immunoglobulin E (FcepsilonRI-beta) on chromosome 11q13 is linked with clinical asthma and certain mutations have been identified. A study was undertaken to identify DNA variation in the FcepsilonRI-beta gene in a population sample in which linkage between 11q13 and asthma was explained by bronchial hyperreactivity (BHR) but not atopy.

METHODS

DNA samples from 71 subjects with asthma, atopy, or BHR were analysed. The complete coding region, some of the introns, and some of the 5' untranscribed region of the FcepsilonRI-beta gene were sequenced.

RESULTS

In the subjects studied there were no deviations from the published sequence in any of the seven coding exons of the FcepsilonRI-beta gene. In particular, the three previously reported mutations (Ile181, Leu183, Glu237) were not detected. Two new polymorphisms were discovered, one at position 243 in the 5' untranscribed region and one at position 4390 in intron III. Neither of these variants showed significant association with asthma, atopy, or BHR.

CONCLUSIONS

These results suggest that, in the population studied, linkage of asthma and BHR to 11q13 is not explained by mutations in the FcepsilonRI-beta gene. Other mutations in the non-coding region of this gene or in adjacent genes must explain the linkage findings in this study.

Genetic linkage of beta and gamma subunits of epithelial sodium channel to systolic blood pressure

BACKGROUND

Mutations in the genes on chromosome 16p12 that encode the beta and gamma subunits of the epithelial sodium channel (SCNNIB and SCNNIG, respectively) have been linked with rare sodium-dependent forms of low and high blood pressure. Other DNA variants in or around these genes may contribute to variation in blood pressure and the risk of coronary heart disease and stroke.

METHODS

We studied 286 white families from the general population in Victoria, Australia. Each family comprised both parents and two natural children. All participants were genotyped at chromosome 16p12 by use of four highly polymorphic microsatellite markers. Quantitative phenotype measurements were correlated with genotype in identity-by-descent sibling-pair linkage analyses.

FINDINGS

We found significant linkage between systolic blood pressure and chromosome 16p12 after parametric analyses (p=0.0003) and non-parametric analyses (p=0.001). The mean difference in systolic blood pressure between siblings identical-by-descent at these loci was half as large (7.1 mm Hg) as the difference between siblings non-identical at these loci (14.0 mm Hg, p=0.001). No linkage between chromosome 16p12 and diastolic blood pressure or body-mass index was observed.

INTERPRETATION

Chromosome 16p12 and the SCNNIB and SCNNIG genes are implicated in the physiological variation of systolic blood pressure. Our findings are important in explaining individual cardiovascular risk within the general population.

Linkage analysis of glucocorticoid and beta2-adrenergic receptor genes with blood pressure and body mass index

Glucocorticoids and catecholamines exert important effects on cardiovascular physiology and metabolism. Variants of the glucocorticoid receptor gene (GRL) and the beta2-adrenergic receptor gene (ADRB2) have been associated with high blood pressure and obesity. These genes are close on human chromosome 5q31-5q32, and we undertook a linkage analysis of this region in 264 families from the general population in relation to systolic and diastolic blood pressure, body mass index, weight, height, and pulse rate. All family members were genotyped at four microsatellite loci (D5S207, D5S210, D5S519, and D5S119) located on chromosome 5q31-5q33.3. Using quantitative identity-by-descent sibling pair linkage analysis, we found that at no loci was genetic similarity associated with phenotypic similarity for systolic and diastolic blood pressure, body mass index, weight, height, or pulse rate. Although it is not possible to exclude the influence of specific combinations of certain GRL and ADRB2 polymorphisms, the absence of significant linkage in our population argues against a role for GRL or ADRB2 in physiological variation of blood pressure and body mass index.

Nerve growth factor gene locus explains elevated renal nerve growth factor mRNA in young spontaneously hypertensive rats

Nerve growth factor (NGF) controls the growth of sympathetic nerves and is increased in young spontaneously hypertensive rats (SHR). The NGF gene has been linked genetically with hypertension in the SHR strain and may explain high NGF mRNA levels. To test for genetic linkage between the NGF gene and its expression in vivo, we examined renal NGF mRNA levels in male SHR, control Donryu rats (DRY), and F2 rats derived from SHR and DRY at ages 2, 4, 10, and 20 weeks. Tail-cuff blood pressure was measured at 4, 10, and 20 weeks of age. NGF mRNA levels in SHR (NGF genotype: SS) were higher than those in DRY (NGF genotype: DD) at 2, 4, and 10 weeks of age (P<0.0001) but the same at 20 weeks of age. In the F2 generation, the S allele was associated with significantly (P=0.01) higher renal NGF mRNA levels at 2 weeks of age. Mean NGF mRNA levels fell (P=0.01) with age in F2 rats, and the difference between SS and DD genotype F2 rats diminished at older ages and was not significant. In F2 rats there was a positive correlation between the number of NGF S alleles inherited and tail-cuff pressure (P<0.007). Our findings indicate that the NGF locus is an important regulator of NGF mRNA levels. It is likely that mutations in or near the NGF gene explain in part high early NGF gene expression in SHR.

Cosegregation of spontaneously hypertensive rat renin gene with elevated blood pressure in an F2 generation

OBJECTIVE

To investigate the role of the renin gene in the hypertension of the spontaneously hypertensive rat (SHR) of the Okamoto strain.

METHODS

We determined whether the SHR renin allele was cosegregated with high blood pressure in 137 F2 rats derived from inbred SHR and Wistar-Kyoto rats. Systolic blood pressure in conscious rats was measured by the tail-cuff method, whereas mean arterial pressure was determined from an indwelling catheter in the left carotid artery. Renin genotypes of F2 rats were determined using a SHR-specific Bg/II restriction fragment length polymorphism that we have previously described.

RESULTS

The SHR renin allele was cosegregated significantly with higher systolic blood pressure in male F2 rats aged 8-24 weeks and in females aged 12-24 weeks. The greatest differences in blood pressure between SHR renin allele homozygotes and Wistar-Kyoto rat renin allele homozygotes were 35 mmHg for males and 17 mmHg for females aged 24 weeks. The SHR renin allele was also associated with a higher mean arterial pressure in rats aged 24 weeks and cosegregated with higher body weight of male F2 rats aged 12-24 weeks but not with that of the females. In contrast to the relationship with blood pressure, the SHR renin allele was segregated with lower plasma renin concentrations in rats aged 24 weeks.

CONCLUSION

These results are consistent with the SHR renin gene being one of the loci determining high blood pressure in rats of this strain, possibly through action at some extra-renal site subserving control of blood pressure.

Human alpha-adducin gene, blood pressure, and sodium metabolism

The adducin genes contribute significantly to population variation in rat blood pressure and cell membrane sodium transport. The 460Trp mutation of the human alpha-adducin gene has been associated with hypertension, in particular hypertension sensitive to sodium restriction. We studied the relationship between the 460Trp mutation and population variation in blood pressure and sodium metabolism. From 603 Scottish families, we selected 151 offspring and 224 parents with blood pressures in either the upper (high) or bottom (low) 30% of the population distribution and measured the 460Trp mutation using allele-specific hybridization. In offspring, we also measured exchangeable sodium, plasma volume, and total body water. Plasma levels of components of the renin-angiotensin system, atrial natriuretic peptide, and cellular sodium and transmembrane sodium efflux were also estimated. The overall frequency of the 460Trp mutation was 27.1%. In offspring and parent groups, we found no difference in the genotype or allele frequencies of the 460Trp mutation between subjects with high or low blood pressure. There was no overall association between the alpha-adducin genotypes and blood pressure variation. In offspring, the 460Trp mutation was not associated with any significant differences in body fluid volumes or exchangeable sodium; levels of plasma renin, angiotensin II, aldosterone, or atrial natriuretic peptide; intracellular sodium; or ouabain-sensitive transmembrane sodium efflux. These findings suggest that in our Scottish population, the alpha-adducin 460Trp polymorphism is not related to blood pressure and does not affect whole body or cellular sodium metabolism.

Genetic analysis of male pattern baldness and the 5alpha-reductase genes

Genetic predisposition and androgen dependence are important characteristics of the common patterned loss of scalp hair known as male pattern baldness. The involvement of the 5alpha-reductase enzyme in male pattern baldness has been postulated due to its role in the metabolism of testosterone to dihydrotestosterone. There are two known isozymes of 5alpha-reductase. Type I has been predominantly localized to the skin and scalp. Type II, also present on the scalp, is the target of finasteride, a promising treatment for male pattern baldness. We conducted genetic association studies of the 5alpha-reductase enzyme genes (SRD5A1 on chromosome 5 and SRD5A2 on chromosome 2) using dimorphic intragenic restriction fragment length polymorphisms. From a population survey of 828 healthy families comprising 3000 individuals, we identified 58 young bald men (aged 18-30 y) and 114 older nonbald men (aged 50-70 y) for a case control comparison. No significant differences were found between cases and controls in allele, genotype, or haplotype frequencies for restriction fragment length polymorphisms of either gene. These findings suggest that the genes encoding the two 5alpha-reductase isoenzymes are not associated with male pattern baldness. Finally, no clear inheritance pattern of male pattern baldness was observed. The relatively strong concordance for baldness between fathers and sons in this study was not consistent with a simple Mendelian autosomal dominant inheritance. A polygenic etiology should be considered.

Independent genetic susceptibility to cardiac hypertrophy in inherited hypertension

Cardiac hypertrophy is a common but not inevitable complication of hypertension. Variation in heart size in hypertensives may reflect independent genetic susceptibility to cardiac hypertrophy. Using an experimental genetic model, we determined the location of quantitative trait loci responsible for cardiac hypertrophy and/or hypertension. We studied 182 F2 male animals derived from a cross of the spontaneously hypertensive rat and normotensive Donryu rats. Direct mean arterial pressure (MAP) and left ventricular (LV) mass were measured at 20 weeks of age, and DNA was obtained for linkage analysis. The estimated heritability of MAP was 62% and for LV mass expressed per unit of body weight (relative LV mass) was 76%. We used 185 polymorphic markers, with an average intermarker distance of 12.3 centimorgans for a genome-wide scan in a representative subgroup of 46 animals to identify preliminary quantitative trait loci, which were then mapped in all 182 male F2 rats. Two loci showed logarithm of the odds scores of > 4.0. One on chromosome 2, Lvm-1, was linked to relative LV mass but showed no evidence of linkage to MAP. Another locus on chromosome 1, Map-1, was linked to MAP. In the same region, a locus Lvm-2 was linked with relative LV mass. These data indicate the existence of a genetic locus on chromosome 2 of the spontaneously hypertensive rat that affects relative LV mass independently of blood pressure.

Persistent reduction in renal nerve growth factor mRNA after perindopril treatment of young spontaneously hypertensive rats

Nerve growth factor (NGF) determines sympathetic innervation of target tissues, and NGF levels are increased in young spontaneously hypertensive rats (SHR). Angiotensin can affect NGF levels, and the persistent reduction in blood pressure after brief angiotensin-converting enzyme inhibition in young SHR may involve long-term changes in NGF and sympathetic innervation. We measured the relative abundance of renal NGF mRNA by reverse transcription-polymerase chain reaction in SHR during and after treatment from 6 to 10 weeks of age with vehicle, perindopril (3 mg/kg per day), the bradykinin B2 antagonist Hoe 140 (0.5 mg/kg per day), both perindopril and Hoe 140, or angiotensin II (Ang II; 200 ng/kg per minute). Glomerular filtration rates were estimated at 10 and 20 weeks of age. At 10 weeks of age, Ang II caused a significant (P<.01) increase and perindopril caused a significant (P<.01) decrease in renal NGF mRNA levels. Blockade of the bradykinin B2 receptor during perindopril treatment attenuated (P<.05) the reduction in NGF mRNA levels. Renal NGF mRNA (P=.005) and blood pressure (P<.001) remained significantly lower than control 10 weeks after perindopril treatment was stopped. The partial reduction in blood pressure at 20 weeks of age in rats that had received perindopril and Hoe 140 was not associated with any difference in renal NGF mRNA. Perindopril-induced long-term reduction in renal NGF mRNA levels may decrease sympathetic innervation and thereby contribute to the long-term posttreatment blood pressure reduction.

Behavioural and cardiovascular responses of rats to euthanasia using carbon dioxide gas

Our results showed more rapid falls in pulse rate and blood pressure in rats euthanized in a chamber precharged with carbon dioxide (CO2), when compared with rats euthanized more slowly, but death still took over 5 min in the former group. There was no behavioural evidence of pain or distress in either group during euthanasia. Initial ataxia and dyspnoea was punctuated by a lag before death, thus separating euthanasia into three clearly defined phases. All visual signs of death preceded complete vascular collapse by about 1 min in both groups, so we recommend that gas flow be maintained for at least 1 min after apparent death.

Absence of genetic linkage of chromosome 5q31 with asthma and atopy in the general population

BACKGROUND

Clinical asthma is associated with increased serum total immunoglobulin E (IgE), atopy (skin prick test positivity to common aeroallergens), and bronchial hyperreactivity (BHR) to non-specific stimuli (positive methacholine challenge test). A region on chromosome 5q31-33 has been linked with increased total serum IgE and BHR. A study of the genetic linkage of this region with clinical asthma and atopy was therefore undertaken.

METHODS

A polymorphic microsatellite marker in chromosome 5q31 (D5S399) was studied in 119 sibling pairs recruited from the general population who shared asthma, atopy, and/or BHR. Based on our population distribution of 13 different alleles, it was expected that by chance alone sibling pairs would share on average 1.24 alleles and that a significant excess would indicate genetic linkage.

RESULTS

No evidence of linkage was found in 45 siblings concordant for asthma (shared alleles = 1.09, p = 0.95), in 103 sibling pairs with atopy (shared alleles = 1.18, p = 0.82), in 51 sibling pairs with BHR (shared alleles = 1.22, p = 0.62), or in 68 sibling pairs who shared atopy in the absence of BHR (shared alleles = 1.22, p = 0.61). A slight non-significant excess of shared alleles (1.44, p = 0.11) was observed in siblings who shared BHR without atopy.

CONCLUSIONS

No evidence of genetic linkage of chromosome 5q31 with either clinical asthma or atopy was therefore detected in the population studied. Linkage between chromosome 5q and BHR needs further investigation.

Linkage analysis of bronchial hyperreactivity and atopy with chromosome 11q13

There are two key clinical features of asthma: allergy and bronchial hyperreactivity (BHR). Some pedigree studies of atopy have indicated linkage with the high affinity IgE receptor (Fc epsilon RI-beta) gene on chromosome 11q13, but others failed to confirm this linkage. We examined the genetic linkage of three polymorphic microsatellite markers to atopy and BHR in 120 affected sibling pairs recruited from the general community. We found no linkage to atopy at any of the three 11q13 loci studied. Our findings also do not favour linkage between BHR and loci approximately 8-9 cM either side of the Fc epsilon RI-beta gene.

Abnormal epinephrine release in young adults with high personal and high parental blood pressures

BACKGROUND

Increased activity of the sympathetic nervous system has been proposed as a cause of high blood pressure (BP) and may be related to diet and body weight. To determine the role of these factors in predisposition to high BP, we studied 100 young adults with high or low BP from families in which both parents had either high or low BP.

METHODS AND RESULTS

Plasma catecholamine, glucose, and insulin levels were measured before and after an oral glucose load. There was a significant correlation between fasting plasma norepinephrine and mean arterial pressure (P=.001). Subjects with high BP, irrespective of parental BP, were heavier (P=.003) and fatter (P=.002) and had a greater rise in plasma insulin (P=.003) following glucose than those with low BP. Offspring with high BP whose parents also had high BP showed an unexpected rise in plasma epinephrine (P=.004) following glucose. This adrenal medullary response was not the result of high parental or high personal BP alone as it was not seen in offspring with low BP whose parents had high BP or in offspring with high BP whose parents had low BP.

CONCLUSIONS

Irrespective of family history, high BP is associated with increased body weight and hyperinsulinemia and reflects personal environment and behavior. However, abnormal epinephrine release is characteristic of the combination of genetic, environmental, and behavioral factors that is associated with high personal BP and a familial predisposition to high BP.

Cardiovascular hypertrophy does not predispose to genetic hypertension

It has been proposed that cardiovascular hypertrophy precedes and contributes to the development of genetic hypertension. In a genetically segregating population we determined whether susceptibility to high blood pressure was associated with cardiovascular structural abnormalities in youth. In 9-week old male F2 rats derived from a cross of spontaneously hypertensive rats (SHR) and inbred normotensive Donryu (DRY) rats we determined left ventricular mass (LVM) by echocardiography and the media-lumen ratio (MLR) of mesenteric resistance vessels by biopsy. Direct mean arterial pressure was measured in the same rats at 20 weeks of age. The ranges of LVM and MLR in young F2 rats encompassed values seen SHR and DRY at this age. However, no correlation was observed between LVM or MLR and subsequent blood pressures at 20 weeks of age. The blood pressure of F2 rats with cardiovascular structural phenotypes within the SHR range was no higher than the remainder of the F2 population. These studies do not support the hypothesis that hypertrophy of the heart or mesenteric resistance vessels confer susceptibility to the development of genetic hypertension.

An appraisal of the genetic approaches to high blood pressure

BACKGROUND

The genetics of high blood pressure is a growing field. Remarkable discoveries have been made in the rare genetic causes of hypertension. However, if molecular biology is to achieve its full potential it must address more common forms of high blood pressure. The genetics of essential hypertension offers great potential but also presents special challenges. This review examines how genes might influence blood pressure, how we might organize the search for underlying genes, where we should look and the way in which genetic knowledge might be used.

NEED FOR BROAD APPROACH

For reasons related to informative research design and the prevention of cardiovascular disease, genetic approaches need to address the variation of blood pressure from low to high levels, not only hypertension.

NEED FOR GENETIC MARKERS

If there is to be a time when DNA testing will be routine, then it will depend on discovering genetic markers that are informative, reliable and cost-beneficial.

Cardiac transplantation, perindopril, and left ventricular hypertrophy in spontaneously hypertensive rats

Angiotensin-converting enzyme inhibitors reduce blood pressure and cardiac mass but may also have a direct effect on myocardial growth. To test this hypothesis, we studied the effects of perindopril on the weight of transplanted hearts in which the left ventricle does not pump blood. Hearts were transplanted between littermate 10-week-old male spontaneously hypertensive rats, and recipients were treated for 2 weeks with vehicle (n = 10), perindopril (3 mg/kg per day) (n = 9), perindopril (3 mg/kg per day) plus the selective bradykinin B2 receptor antagonist Hoe 140 (500 micrograms/kg per day) (n = 13), or angiotensin II (200 ng/kg per minute) (n = 12). Perindopril reduced blood pressure and native left ventricular weight and also caused a significant decrease in the weight of the transplanted left ventricle compared with controls. Hoe 140 did not significantly alter blood pressure or native left ventricular weight of perindopril-treated rats but caused a significant increase in the weight of the transplanted left ventricle compared with rats treated with perindopril alone. Angiotensin treatment resulted in a significant increase in blood pressure and native left ventricular weight but no significant change in the weight of the transplanted left ventricle. Blood pressure and left ventricular weight for native but not for transplanted hearts were positively correlated. Therefore, in the absence of mechanical load, the weight of the left ventricle of spontaneously hypertensive rats responds little to angiotensin II but can be reduced by angiotensin-converting enzyme inhibition. The effect of perindopril on transplanted hearts of spontaneously hypertensive rats appears to depend on bradykinin.

Low affinity nerve growth factor receptor gene co-segregates with decreased bodyweight and increased left ventricular weight in spontaneously hypertensive rats

1. The sympathetic nervous system influences the cardiovascular and hormonal systems and sympathetic innervation is dependent on nerve growth factor (NGF). The NGF gene is linked genetically to high blood pressure in the spontaneously hypertensive rat (SHR) and there exists a mutation in the SHR low affinity NGF receptor (LNGFR) gene. 2. To determine whether the LNGFR mutation was linked genetically with cardiovascular phenotypes we studied an F2 population derived from SHR and normotensive Donryu (DRY) rats. 3. Mean arterial pressure (MAP), left ventricular mass (LVM) and related phenotypes were measured in 127 20 week old male F2 rats and correlated with the inheritance of the SHR mutation (S) and/or the DRY allele (D) of the LNGFR. 4. Analysis of variance revealed that the S mutation was associated with a significantly lower bodyweight in F2 rats (P < 0.0001). 5. The S mutation was associated with a significant (P < 0.007) increase in LVM:bodyweight ratio, but not with differences in right ventricular or kidney weights corrected for bodyweight. We found no association between MAP and LNGFR alleles or genotypes. 6. These results suggest that the mutation in the signal peptide of LNGFR may serve as a useful marker for the analysis of genetic factor(s) involved in the differential determination of body size and heart weight.

Plasma angiotensin II, predisposition to hypertension, and left ventricular size in healthy young adults

BACKGROUND

We studied the correlates of left ventricular mass (LVM) in 84 healthy young adults aged 16 to 24 years from the general population. Subjects were selected according to predisposition to hypertension into four groups with either high or low personal blood pressures and either high or low parental blood pressures.

METHODS AND RESULTS

LVM was measured by echocardiography, and measurements of blood pressure, heart rate, body dimensions, and plasma concentrations of components of the renin-angiotensin system were made under resting conditions. LVM was similar in individuals predisposed to hypertension (high personal and parental blood pressures) and those with contrasting predisposition (low personal and parental pressures). Regression analysis of the combined groups showed that LVM correlated closely with body size, particularly lean body mass (r=.69, P<.0001) and systolic (r=.35, P<.0001) but not diastolic blood pressure. Plasma angiotensin II (r=.39, P<.0001), renin (r=.302, P<.01), and angiotensin-converting enzyme (r=.22, P<.05) showed significant correlation with LVM. Multiple regression analysis revealed that plasma angiotensin II was the most important component of the renin-angiotensin system and that its effect was independent of systolic blood pressure and body size.

CONCLUSIONS

These findings provide evidence in humans that angiotensin II exerts a direct on myocardial size. This association may have important implications for the complications and treatment of left ventricular hypertrophy.

Nerve growth factor gene and hypertension in spontaneously hypertensive rats

OBJECTIVE

High blood pressure in spontaneously hypertensive rat (SHR) is associated with increased sympathetic innervation of key tissues, possibly as the result of increased nerve growth factor (NGF). The aim of this study was to test for genetic linkage of the NGF gene to high blood pressure.

DESIGN

We studied NGF gene expression in young SHR and examined linkage of the NGF locus to mean arterial pressure in genetically segregating crosses of SHR and normotensive Donryu (DRY) rats.

METHODS

NGF mRNA was measured by Northern blot, and a restriction fragment length polymorphism of the NGF gene revealed after digestion with the NsiI restriction enzyme was used to study inheritance.

RESULTS

Levels of NGF mRNA were detected easily in the kidneys of 2-, 4- and 10-week-old SHR but not in age-matched DRY rats. In an F2 population, the blood pressure of rats homozygous for the DRY NGF allele was 6 mmHg less than in heterozygotes and 8 mmHg less than in rats homozygous for the SHR NGF allele (analysis of variance, P < 0.004). In backcross rats the blood pressure of NGF heterozygotes was not significantly different from that of SHR homozygotes.

CONCLUSION

These results indicate differences in renal NGF mRNA in SHR during the development of hypertension and suggest that a genetic locus in or near the NGF gene contributes in a Mendelian dominant pattern to a significant increment in blood pressure in SHR.

Linkage of high-affinity IgE receptor gene with bronchial hyperreactivity, even in absence of atopy

Asthma is a manifestation of bronchial hyperreactivity (BHR) and forms part of the spectrum of atopic disease. Some pedigree studies of atopy have suggested linkage with the high-affinity IgE receptor (Fc epsilon RI beta) gene on chromosome 11q13, but others find no linkage. The molecular genetics of asthma and BHR have not been studied in the general population. We examined the genetic linkage of the Fc epsilon RI beta gene with clinical asthma and the underlying phenotypes of BHR (to methacholine) and atopy (defined by skinprick testing) in 123 affected sibling-pairs recruited from the general population. We found evidence of significant linkage of a highly polymorphic microsatellite marker in the fifth intron of the Fc epsilon RI beta gene to a diagnosis of asthma (18.0% excess of shared alleles, p = 0.002) and to BHR (21.7% excess of shared alleles, p = 0.001). Significant linkage was also observed in siblings sharing BHR when those with atopy were excluded (32.8% excess of shared alleles, p = 0.004). Atopy in the absence of BHR did not show significant linkage to the Fc epsilon RI beta gene (7.2% excess of shared alleles, p = 0.124). These findings suggest that mutations in the Fc epsilon RI beta gene or a closely linked gene influence the BHR underlying asthma, even in the absence of atopy.