Biological and cultural determinants of blood pressure

Genetic screening in arterial hypertension

Studies involving adoptive families and twins have demonstrated the genetic basis of hypertension and shown that genetic factors account for about 40% of the variance in blood pressure among individuals. Arterial hypertension is genetically complex: multiple genes influence the blood pressure phenotype through allelic effects from single genes and gene-gene interactions. Moreover, environmental factors also modify the blood pressure phenotype. This complexity explains why the identification of the underlying genes has not been as successful in hypertension as in other diseases (such as type 1 and type 2 diabetes mellitus). The identification of the genetic determinants of hypertension has been most successful in endocrine forms of hypertension, which have well-defined phenotypes that permit a precise patient stratification into homogeneous cohorts. A promising area for the application of genetic testing to personalized medicine is the prediction of responses and adverse reactions to antihypertensive drugs. The identification of genetic markers of drug response will enable the design of randomized controlled trials in much smaller series of patients than is currently possible, decreasing the costs and times from drug design to clinical use and ultimately providing patients and doctors with a larger number of tools to combat hypertension, the most important risk factor for cardiovascular disease. This Review focuses on the rapidly developing field of genetic testing in patients with arterial hypertension.

Major gene effects in systolic and diastolic blood pressure in families receiving a health examination in Taiwan

BACKGROUND

Genetic factors play an important role in determining blood pressure values. Strong familial aggregation and estimated heritability values around 0.4-0.6 were reported in a white population.

OBJECTIVES

To investigate the genetic components and mode of inheritance of blood pressure in Taiwan.

DESIGN

A cross-sectional family study based on an adult population undergoing a health examination.

SETTING AND PARTICIPANTS

A total of 1313 adults and their spouses or first-degree relatives, or both, underwent a health examination in a tertiary university hospital from August 1998 to September 1999.

MAIN OUTCOME MEASURES

Genetic analyses, including comingling analysis, familial correlation and complex segregation analysis, were used to detect the genetic components and the mode of inheritance of blood pressures.

RESULTS

In both systolic and diastolic blood pressure, the comingling analyses demonstrated that a more than one-component distribution provided the best fit for the data. The familial correlation coefficients showed significant parent-offspring and sibling correlation. Complex segregation analyses showed major gene effects in controlling systolic and diastolic blood pressure.

CONCLUSIONS

There were significant genetic components in blood pressure among Taiwanese. Further investigation of genomic loci for the control of blood pressure is indicated.

Genetic and environmental influences on blood pressure in elderly twins

We used 289 pairs of Swedish twins reared apart or together to evaluate the importance of genetic and environmental influences on blood pressure. Unlike other twin and family studies, the adoption/twin design allows a distinction between estimates of the importance of shared rearing environments and genetic effects. Genetic factors were observed to play an important role for individual differences in blood pressure. Model-fitting analyses suggested upper limits of heritability for systolic and diastolic blood pressures in the entire sample of 0.44 and 0.34, respectively. More interestingly, substantial influences of shared family effects accounting for up to 27% of the variation were also revealed. Effects of correlated environment, which might reflect, for example, the intrauterine environment, existed to some extent later in life. The influence of genetic factors tended to decrease across age groups for systolic blood pressure (0.62 in individuals less than 65 years old; 0.12 in those 65 years and older) but not for diastolic blood pressure (0.22 for the middle-aged group; 0.26 for the older group). However, this declining trend for systolic blood pressure did not reach significance (chi 2 = 8.07, df = 4, P = .09).

Genetic and environmental effects on coronary heart disease risk factors in northern Norway. The cardiovascular disease study in Finnmark

This study comprised 1377 first degree relatives in 575 families ascertained through a comprehensive screening of the general population from 20 to 52 years of age. Path analysis using parsimonious models gave evidence of significant biologic and environmental transmission for total cholesterol (genetic and cultural heritabilities were 0.46 and 0.05, respectively), high density lipoprotein cholesterol (0.42, 0.10), triglycerides (0.21, 0.07), and systolic (0.48, 0.04) and diastolic (0.35, 0.05) blood pressure. Compared with other studies employing the same path analytic model, heritability estimates in general were among the highest reported, except for the somewhat lower genetic component in total cholesterol and triglycerides. For the first time in a single sample from the general population, lipid and blood pressure variables were investigated applying the same methodology, and good agreement was illustrated by the result that identical parsimonious models were reached for all phenotypes, with the exception of a single additional parameter for total cholesterol. About one fourth to one half of the total phenotypic variance could be ascribed to genetic sources, whereas the contribution from shared familial environment was much smaller.

Age and blood pressure changes. A 20-year follow-up study in nuns in a secluded order

In a prospective study, 144 white nuns belonging to a secluded monastic order and 138 white control laywomen were followed for 20 years to investigate whether living for a long time in a stress-free environment influences the effect of aging on blood pressure. Silence, meditation, and isolation from society are the distinctive features of the life-style examined. At study entry, blood pressure was not dissimilar in the nuns and the control group, but it increased over time only in the controls, with a mean slope of the regression line (beta coefficient) of 0.089 in the nuns (NS) and 2.171 in the controls (p less than 0.0001) for systolic blood pressure and of 0.054 in the nuns (NS) and 0.742 in the controls (p less than 0.0001) for diastolic blood pressure. Weight and body mass index increased similarly over time in the two groups. Family history of hypertension was not dissimilar between the groups. Serum cholesterol and triglycerides, higher at study entry in the nuns, increased similarly over time in the two groups. Twenty-four-hour urinary sodium excretion, collected randomly in both groups, did not differ over time between nuns and controls. None of the women smoked or used oral contraceptives. Educational level was higher in the control group, but subgroups of 48 nuns and 52 laywomen of comparable educational level maintained the same difference in the blood pressure trend over time as in the main cohort. Parity affected the increase of systolic, but not of diastolic, blood pressure with age among the laywomen, but nuns and no-childbirth controls maintained a significantly different blood pressure trend over time.(ABSTRACT TRUNCATED AT 250 WORDS)

A developmental hypothesis for adult blood pressure

Observed increases in phenotypic variance for blood pressure during adulthood are a predictable consequence of an a priori model for developmental change and continuity previously applied to cognitive development. The implications of this model for genetic and environmental covariances depend on the mechanism which maintains developmental continuity. Using data from young adult twins and their parents, it is shown how traditionally estimated genetic and environmental parameters may be reinterpreted in the light of the developmental model. Illustrative data suggest a hypothesis that genetic effects on blood pressure are largely temporally pleiotropic, acting consistently but not cumulatively throughout adulthood, while environmental influences act haphazardly but their effects are transmitted forward with high fidelity.

A family study of developmental effects upon blood pressure variation

In an earlier study of blood pressure variation in middle aged parents and their young adult twin offspring, the greater blood pressure variation observed in the parent sample was accounted for in terms of an increasing influence of individual environmental experiences with increasing age and a commensurate reduction in the impact of heredity. In the present study, the sample size was enlarged to provide a more powerful test of these effects. Maximum likelihood model-fitting techniques were applied to blood pressure covariation in balanced pedigrees, consisting of 85 families (40 MZ and 45 DZ twin pairs). As before, our analysis indicated that a developmental effect was a salient factor in the older age group.

Risk factors for coronary artery disease in families of young men with myocardial infarction

Familial clustering of coronary artery disease (CAD) and familial influences on various clinical and metabolic risk factors were investigated in 85 male survivors of acute myocardial infarction younger than 45 years. The study also involved 85 age-matched men randomly selected from the general population and the first-degree relatives of both patients and control subjects. Presence of CAD was assessed by an angina questionnaire and from rest and exercise electrocardiograms. There was an apparent aggregation of premature CAD in 38% of the case families. A familial clustering of hyperlipoproteinemia was present in 58% of the case families and 15% of the control families. Systemic hypertension and cigarette smoking also were clustered in the case families. Multivariate statistical analyses of clinical and metabolic risk indicators in patients with and without a family history of CAD and in control subjects indicated that familial aggregation of CAD is independently related to MI at a young age. Degree and extent of coronary atheromatosis and number and severity of hemodynamically significant stenoses did not differ between young patients with and without a familial aggregation of CAD. The absence of a relation between the family history and severity of CAD implies that other underlying mechanisms are involved.

Familial and individual influences on blood pressure

Although familial aggregation of blood pressure is well documented, few studies have considered the changing contribution of genetic and environmental influences during adulthood. Applying maximum likelihood model fitting to blood pressure covariation in balanced pedigrees including both parents and their young adult twin offsprings (25 MZ, 32 DZ, aged between 16 and 24 years), it is shown that the increased variation in parents is explained by such developmental changes. For DBP, an apparent reduction in heritability from 68% to 38% from young adulthood to middle age results from the increasing impact of individual environmental experience (E1), with little or no influence from shared family environmental (E2). For SBP, shared environmental effects may play a part. Given the relatively small size of the present sample, the conclusions are to be seen as tentative. An augmented family study, incorporating middle aged twins and their young adult offspring, will clarify the causation of these developmental changes.

Factor analysis suggesting contrasting determinants for different blood pressure measurements

A multiple regression analysis was performed on statistically independent factors derived from blood pressure measurements and possible predictive variables in 618 Utah adults. Nine blood pressure factors obtained in a previous study composed the dependent variables; 35 anthropometric, questionnaire, and biochemical variables were reduced by factor analysis to 10 factors and used as independent variables. Body size and obesity had significant independent effects on different types of blood pressure: body size correlated most highly with systolic blood pressure, while obesity correlated most highly with sitting diastolic blood pressure measurements. Smoking did not correlate with sitting blood pressure but did show a significant positive correlation (after controlling for obesity) with tilt and supine diastolic pressure. Alcohol consumption correlated positively with sitting diastolic pressure when the effects of body size and obesity were controlled. No correlations were found between urinary potassium or sodium excretion and any blood pressure factors, but a significant positive correlation was seen between plasma sodium concentration and several different types of diastolic blood pressure measurements. Psychological stress showed a significant independent positive correlation with systolic blood pressure measurements that was strongest in adults over 35 years of age. The multiple correlation values for the multiple regression equations ranged from 0.19 to 0.52.