Multivariate genetic analysis of blood pressure and body size. The Medical College of Virginia Twin Study

Genetic and Environmental Influences on Blood Pressure and Body Mass Index in the National Academy of Sciences-National Research Council World War II Veteran Twin Registry

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Blood pressure (BP) and obesity phenotypes may covary due to shared genetic or environmental factors or both. Furthermore, it is possible that the heritability of BP differs according to obesity status—a form of G×E interaction. This hypothesis has never been tested in White twins. The present study included 15 924 White male twin pairs aged between 15 and 33 years from the National Academy of Sciences–National Research Council World War II Veteran Twin Registry. Systolic and diastolic BPs, as well as height and weight, were measured at the induction physical examination. Body mass index (BMI) was used as the index of general obesity. Quantitative genetic modeling was performed using Mx software. Univariate analysis showed that narrow sense heritabilities (95% CI) for systolic BP, diastolic BP, height, and BMI were 0.401 (0.381–0.420), 0.297 (0.280–0.320), 0.866 (0.836–0.897), and 0.639 (0.614–0.664), respectively. Positive phenotypic correlations of BMI with systolic BP (r=0.13) and diastolic BP (r=0.08) were largely due to genetic factors (70% and 86%, respectively). The gene-BMI interaction analysis did not show any support for a modifying effect of BMI on genetic and environmental influences of systolic BP and diastolic BP. Our results suggest that correlations between BP and BMI are mainly explained by common genes influencing both. Higher BMI levels have no influence on the penetrance of genetic vulnerability to elevated BP. These conclusions may prove valuable for gene-finding studies.

Heritability and genetic correlations of obesity indices with ambulatory and office beat-to-beat blood pressure in the Oman Family Study

OBJECTIVE

To more precisely and comprehensively estimate the genetic and environmental correlations between various indices of obesity and BP.

METHODS

We estimated heritability and genetic correlations of obesity indices with BP in the Oman family study (n = 1231). Ambulatory and office beat-to-beat BP was measured and mean values for SBP and DBP during daytime, sleep, 24-h and 10 min at rest were calculated. Different indices were used to quantify obesity and fat distribution: BMI, percentage of body fat (%BF), waist circumference and waist-to-height ratio (WHtR). SOLAR software was used to perform univariate and bivariate quantitative genetic analyses adjusting for age, age, sex, age-sex and age--sex interactions.

RESULTS

Heritabilities of BP ranged from 30.2 to 38.2% for ambulatory daytime, 16.8--21.4% for sleeping time, 32.1--40.4% for 24-h and 22--24.4% for office beat-to-beat measurements. Heritabilities for obesity indices were 67.8% for BMI, 52.2% for %BF, 37.3% for waist circumference and 37.9% for WHtR. All obesity measures had consistently positive phenotypic correlations with ambulatory and office beat-to-beat SBP and DBP (r-range: 0.14--0.32). Genetic correlations of obesity indices with SBP and DBP were higher than environmental correlations (rG: 0.16--0.50; rE: 0.01--0.31).

CONCLUSION

The considerable genetic overlap between a variety of obesity indices and both ambulatory and office beat-to-beat BP highlights the relevance of pleiotropic genes. Future GWAS analyses should discover the specific genes both influencing obesity indices and BP to help unravel their shared genetic background.

Familial aggregation and childhood blood pressure

There is growing concern about elevated blood pressure (BP) in children. The evidence for familial aggregation of childhood BP is substantial. Twin studies have shown that a large part of the familial aggregation of childhood BP is due to genes. The first part of this review provides the latest progress in gene finding for childhood BP, focusing on the combined effects of multiple loci identified from the genome-wide association studies on adult BP. We further review the evidence on the contribution of the genetic components of other family risk factors to the familial aggregation of childhood BP including obesity, birth weight, sleep quality, sodium intake, parental smoking, and socioeconomic status. At the end, we emphasize the promise of using genomic-relatedness-matrix restricted maximum likelihood (GREML) analysis, a method that uses genome-wide data from unrelated individuals, in answering a number of unsolved questions in the familial aggregation of childhood BP.

Probing genetic overlap in the regulation of systolic and diastolic blood pressure in Danish and Chinese twins

Although the phenotypic correlation between systolic blood pressure (SBP) and diastolic blood pressure (DBP) is well known, the genetic basis for the correlation has rarely been investigated. The aim of this paper is to examine the genetic overlap between SBP and DBP by fitting bivariate models to Danish and Chinese twins and comparing ethnic differences between the two samples. Our estimates revealed a high proportion of additive genetic components shared by both SBP and DBP in Danish (0.71, 95% confidence interval (CI): 0.65-0.75) and Chinese (0.62, 95% CI: 0.50-0.71) twins with no statistically significant ethnic differences. The estimated genetic component in phenotypic correlation could serve to guide molecular genetic studies searching for genetic variants that affect both SBP and DBP. The bivariate model also estimated genetic and environmental contributions to SBP and DBP separately, with an overall pattern of higher genetic regulation or heritability in Danish (0.72, 95% CI: 0.67-0.76 for SBP; 0.70, 95% CI: 0.65-0.75 for DBP) than in Chinese (0.54, 95% CI: 0.44-0.63 for SBP; 0.57, 95% CI: 0.47-0.65 for DBP) twins and a higher contribution from unique environmental factors in Chinese compared with Danish twins. The estimated contribution from unique environmental factors suggests that promoting healthy lifestyles may provide an efficient way of controlling high blood pressure, particularly in the Chinese population.

Genetic and environmental influences on blood pressure and body mass index in Han Chinese: a twin study

The familial aggregation of blood pressure (BP) may be partly due to the familial aggregation of obesity, caused by genetic and/or environmental factors that influence both. Gene-obesity interactions are expected to result in different heritability estimates for BP at different obesity levels. However, the latter hypothesis has never been tested. The present study included 1243 monozygotic and 833 dizygotic Han Chinese twins (mean±s.d. age: 37.81 ± 9.82; range: 19.1-81.4) from the Chinese National Twin Registry. Body mass index (BMI) was used as the index of general obesity. The outcome measures were systolic BP (SBP) and diastolic BP (DBP). Quantitative genetic modeling was performed using Mx software. The SBP and DBP heritabilities were 46 and 30%, respectively. The positive correlations of BMI with SBP (r=0.26) and with DBP (r=0.27) were largely due to genetic factors (approximately 85%). Genetic factors, which also influence BMI, account for 6 and 7% of the total variance for SBP and DBP, respectively. The gene-obesity interaction analysis showed that both common and unique environmental influences on SBP increased with increasing levels of BMI, resulting in a lower heritability at higher BMI levels, whereas for DBP the heritability remained unchanged at higher BMI levels. Our results suggest that higher BMIs may reduce SBP heritability through a larger impact of environmental effects. These conclusions may be valuable for gene-finding studies.

Genetic and environmental influences on body fat and blood pressure in African-American adult twins

OBJECTIVE

African Americans have a particularly high prevalence of excessive body fat and high blood pressure. Genetic and environmental influences may be implicated for both of these risk factors. We investigated the potential for common genetic and environmental influences on body fat (waist circumference (WC), body mass index (BMI)) and blood pressure measures (systolic and diastolic pressure (SBP, DBP)) among African-American male and female subjects.

RESEARCH METHODS AND PROCEDURES

Measurements were taken as part of the Carolina African-American Twin Study of Aging (CAATSA). The CAATSA sample contains 217 same-sex African-American male and female twins with average age of 47 years. This analysis included 39 monozygotic male pairs (MZ), 43 dizygotic male pairs (DZ); 63 MZ female pairs, and 72 DZ female pairs. Maximum likelihood quantitative genetic analyses were used.

RESULTS

The total genetic variance for SBP was 22% in male subjects and 40.1% in female subjects. Of this total variance, 3.1% was in common with BMI in male subjects and 6% was in common with BMI in female subjects. After controlling for the effects of BMI, WC had less than 1% of its variance in common with SBP in male and female subjects. For DBP, the total genetic variance was 16.9% in male and 38.7% in female subjects. Of this total variance 6.1% was in common with BMI in male subjects and 3.7% was in common in female subjects. Again, WC had less than 1% of its genetic variance in common with DBP in both male and female subjects. The environmental variance common among these measures was also very small. The remaining variance was primarily accounted for by genetic and environmental effects unique to each measure as well as age.

DISCUSSION

Based on the very small common genetic variance for BMI, SBP, and DBP as well as WC and the blood pressure measures, our results suggest that searching for common genes among these measures may be inconclusive.

Moderators of blood pressure development from childhood to adulthood: a 10-year longitudinal study

OBJECTIVE

To examine the effect of ethnicity on the development of blood pressure (BP) from childhood into early adulthood within the context of height, sex, adiposity, and socioeconomic status (SES).

STUDY DESIGN

Individual growth curves of systolic BP (SBP) and diastolic BP (DBP) were created for 745 black and white male and female youths, with annual assessments over a 10-year period (age range, 4.9-27.5 years).

RESULTS

Blacks had higher SBP levels (P <0.01) than whites, respectively. Moreover, black female subjects showed a greater SBP increase over time (P <.05) than white female subjects. Black male and female subjects also showed higher DBP levels (P <.001) than white male and female subjects, respectively, but the rate of change of DBP did not differ. Ethnic differences in BP trajectories persisted after adjusting for SES and/or changes in height and/or adiposity in both male and female subjects.

CONCLUSIONS

Ethnic differences in SBP become manifest in childhood in girls, in early adolescence in boys, and tend to increase with age. Ethnic differences in DBP become manifest in childhood in both boys and girls and remain stable over time. The ethnic differences cannot be entirely explained by individual differences in SES, growth, or adiposity. Identification of mechanisms responsible for increase of BP in childhood will improve prevention of hypertension in adulthood.

Neonatal sympathectomy reduces adult blood pressure and cardiovascular pathology in Y chromosome consomic rats

The hypothesis was tested that the sympathetic nervous system (SNS) developmentally influences circulating testosterone (T), systolic blood pressure (SBP) and cardio-renal pathology in SHR/y animals. A sympathoplegic drug, guanethidine, and an antibody to nerve growth factor were administered to WKY and borderline hypertensive SHR/y male rats (n = 20/group) for the first 3 weeks of life; control groups (n = 20/group) received saline. SBP, serum T and luteinizing hormone (LH) were measured. SBP in the WKY and SHR/y sympathectomy (sympx) groups decreased 10mmHg (p < 0.001) and 50mmHg (p < 0.001), respectively, when compared to their control groups. Serum T levels in the sympx WKY group were lower (p < 0.01) than those in controls, and the rise of T typically observed in SHR/y from weeks 6-8 was delayed in the sympx SHR/y group, similar to the pattern in WKY. Serum LH levels were increased in the sympx WKY group, but not in the SHR/y group. Sympx caused a greater reduction in renal glomerular changes (p < 0.01), coronary artery collagen deposition (p < 0.01) and myocardial fibrosis (p < 0.01) in SHR/y than WKY rats. In conclusion, the SHR Y chromosome has a locus that enhances SNS activity, which can raise SBP and result in renal and cardiovascular tissue damage.

Complex segregation analysis of blood pressure and heart rate measured before and after a 20-week endurance exercise training program: the HERITAGE Family Study

Complex segregation analysis of baseline resting blood pressure (BP) and heart rate (HR) and their responses to training (post-training minus baseline) were performed in a sample of 482 individuals from 99 white families who participated in the HERITAGE Family Study. Resting BP and HR were measured at baseline and after a 20-week training program. Baseline resting BP and HR were age-adjusted and age-BMI-adjusted, and the responses to training were age-adjusted and age-baseline-adjusted, within four gender-by-generation groups. This study also analyzed the responses to training in two subsets of families: (1) the so-called "high" subsample, 45 families (216 individuals) with at least one member whose baseline resting BP is in the high end of the normal BP range (the upper 95th percentile: systolic BP [SBP] > or = 135 or diastolic BP [DBP] > or = 80 mm Hg); and (2) the so-called "nonhigh" subsample, the 54 remaining families (266 individuals). Baseline resting SBP was influenced by a multifactorial component (23%), which was independent of body mass index (BMI). Baseline resting DBP was influenced by a putative recessive locus, which accounted for 31% of the variance. In addition to the major gene effect, which may impact BMI as well, baseline resting DBP was also influenced by a multifactorial component (29%). Baseline resting HR was influenced by a putative dominant locus independent of BMI, which accounted for 31% of the variance. For the responses to training, no familiality was found in the whole sample or in the nonhigh subsample. However, in the high subsample, resting SBP response to training was influenced by a putative recessive locus, which accounted for 44% of the variance. No familiality was found for resting DBP response to training. Resting HR response to training was influenced by a major effect (accounting for 35% of the variance), with an ambiguous transmission from parents to offspring.

Cross-trait familial resemblance for resting blood pressure and body composition and fat distribution: The HERITAGE family study

Cross-trait familial resemblance between resting blood pressure (BP) and body composition and fat distribution was examined in 98 Caucasian families participating in the HERITAGE Family Study by using a multivariate familial correlation model assessing both intraindividual and interindividual cross-trait correlations. The 520 family members were sedentary at baseline examination, and both resting systolic (SBP) and diastolic (DBP) BP were cross-analyzed with each of the following 10 indications of body composition and fat distribution: percent body fat (%BF), abdominal visceral fat (AVF), body mass index (BMI), fat-free mass (FFM), fat mass (FM), sum of eight skinfolds (SF), total abdominal fat (TAF), ratio of trunk-to-extremity skinfolds (TER), waist circumference (WAIST), ratio of waist-to-hip circumferences (WHR). Five of the variables were also corrected for fat mass (AVFf, TAFf, TERf, WAISTf, WHRf) to index these measures independent of total degree of adiposity. In general, the results suggested strictly intraindividual cross-trait resemblance, with occasional spouse cross-trait resemblance, but few or no sibling or parent-offspring cross-trait correlations. This pattern is largely consistent with nongenetic specific environmental determinants for the BP-body composition and fat distribution covariation, with possibly some common environmental influence between spouses and negligible genetic effects. The only findings suggesting any familial cross-trait resemblance were significant sibling correlations for DBP-FFM and DBP-WHR, although the parent-offspring correlation was not significant. These findings suggest that the observed BP-body composition and fat distribution cross-trait correlations in these sedentary families are probably not due to multifactorial effects such as polygenic and/or common familial environmental effects. Whether or not other factors such as nonadditive effects are involved warrants further investigation using other methods. Am. J. Hum. Biol. 12:32-41, 2000. Copyright 2000 Wiley-Liss, Inc.

Genetic and environmental causes of covariation among blood pressure, body mass and serum lipids during young adulthood: a twin study

OBJECTIVE

To determine the extent to which the correlation of systolic blood pressure, diastolic blood pressure, body mass, fasting total cholesterol and fasting triglycerides in young adulthood reflects common genetic or environmental influences.

DESIGN

Cardiovascular risk factors were measured in a community sample of 129 monozygotic and 67 dizygotic twin pairs, ages 18-30 years.

METHODS

Multivariate twin structural equation modelling allows estimation of the extent to which the covariation of two or more variables is attributable to common genetic and environmental factors and was used to analyse the correlation among systolic blood pressure, diastolic blood pressure, body mass index, fasting total cholesterol and triglycerides.

RESULTS

The covariation of risk factors was partially attributable to a single common genetic factor, while the covariation of systolic blood pressure, body mass index and triglycerides was also, in part, attributable to a common non-shared environmental factor.

CONCLUSIONS

Genetic and, to a lesser extent, non-shared environmental factors contribute to the covariation of cardiovascular risk factors in young adult twins. Nonetheless, it should be noted that these common influences account for a relatively small percentage of the variance in each risk factor compared to genetic and environmental factors that are risk factor-specific.

Familial aggregation of cardiovascular disease risk factors: the Cuenca Study

OBJECTIVE

The familial aggregation of lipid levels, blood pressure, and body mass index (BMI) was studied in schoolchildren in Cuenca, Spain.

METHODS

A cross-sectional observation study was made of 307 schoolchildren of both sexes, age range 9-12 years, from three schools in Cuenca, Spain, and of 346 parents. Social and demographic variables, weight, height, body mass index, systolic blood pressure, diastolic blood pressure, and fasting plasma concentrations of total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides were evaluated.

RESULTS

The Spearman coefficients of correlation for total cholesterol, LDL-cholesterol, and BMI for parents and daughters were 0.34-0.42 (P < 0.01). These coefficients of correlation for parents and sons were lower (P > 0.05). The coefficient of correlation for blood pressure in parents and sons was low (P < 0.05). None of the variables showed any coefficient of correlation between spouses. The sexual differences in the correlations between the levels of the different variables were confirmed by multiple regression analysis. Total cholesterol and LDL-cholesterol levels and BMI accounted for larger percentages of variability in these parameters in daughters than in sons. The paternofilial aggregation of HDL-cholesterol and triglyceride levels was weak. The only variable that accounted for a significant variability in blood pressure (systolic and diastolic) was weight in children of both sexes.

CONCLUSIONS

The familial aggregation of lipid levels and body mass index showed sex differences. The paternofilial aggregation of blood pressure was weak. There was no relation between spouses.

Familial and genetic influences on heart rate variability

The authors tested the hypothesis of a genetic influence on heart rate variability (HRV). This genetic influence was assessed in 62, twin pairs (30 monozygotic, 32 dizygotic). From all twins, long-term electrocardiographic records were obtained, edited, and analyzed. Heart rate variability analysis was performed on the basis of parameters from time-domain, frequency-domain, and nonlinear dynamics. First, the parameter distances between the two twins of a pair and between one of the two and a third randomly selected person of another age-matched twin pair (ST1) were compared. Second, the parameter distances between the two twins and the averaged parameter distances of these two twins to all other age-matched persons (ST2) were compared. Finally, the averaged differences in parameter values between monozygotic and dizygotic age-matched twin pairs were compared. For statistical analysis, the nonparametric Wilcoxon's matched-pair signed rank test and parametric t-test for paired samples were used. Twin pairs show a significant lower difference in parameter values than other randomly selected and age-matched couples (P < .001 in ST1 and ST2). This reflects a considerable familial influence. Most parameters of the time-domain, none of the frequency-domain, and half of the nonlinear dynamics show significant differences between twin pairs and nontwin pairs. As a result of the comparison between monozygotic and dizygotic twin pairs, a significant lower parameter difference in the monozygotic pairs (P < .05) is found. These results suggest that there is a genetic component in heart rate generation and HRV, in addition to family environmental influences. Analysis of HRV might become a useful method in phenotyping severe genetic changes in cardiovascular diseases.

Body mass index of Saudi children ages six to 16 years from the eastern province

Body mass index (BMI) is generally accepted as a useful index of various clinical situations related to obesity. However, there are no reference BMI charts for Saudi children; this paper is an attempt to establish these. A total of 21,638 Saudi schoolchildren between ages six to 16 years (49.6% males) were studied. Curves for BMI, seven percentiles - 5th, 10th, 25th, 50th, 75th, 90th and 95th - were constructed. As a reference material, BMI data for American children were modified into Hegira years. It was found that, in agreement with others, the BMI for the Saudi children studied was age- and gender-dependent. Comparison between Saudi data and international reference showed the expected genetic influence. These results remain to be compared with those from other regions in the Kingdom.

Transluminal extraction atherectomy and adjunctive balloon angioplasty for restenosis after Palmaz-Schatz coronary stent implantation

Two patients who developed restenosis after implantation of Palmaz-Schatz coronary stents were successfully treated by transluminal extraction atherectomy and there has been no recurrence on follow-up angiograms. The optimum strategy for managing restenosis after coronary stenting remains unclear, but transluminal extraction atherectomy appears to be a safe and effective option.

Genetic factors that predispose the child to develop hypertension

Familial aggregation, population, and twin studies all point to important genetic influences on the level of blood pressure in childhood and adolescence. Whether a major gene effect operates during childhood has not been determined. The investigation of polygenic paths leads to the study of variables such as ion transport and reactivity paths that appear to be under strong genetic influences. The evidence suggests that abnormalities in these paths might be linked to a prehypertensive state. Univariate genetic analyses of systolic and diastolic blood pressure show that a significant portion of the variability of these variables is under genetic control. Moreover, during early adolescence, boys differ from girls in the regulation of their resting blood pressure. Multivariate genetic analyses show that in these young adolescents, genetic paths shared with body mass index appear to influence systolic but not diastolic blood pressure. The genetic relationship between systolic and diastolic blood pressure appears largely to be independent of body mass index. Genetic studies can partition the genetic and environmental influences on blood pressure and identify shared paths with variables previously believed to be linked epidemiologically. This information may have the capacity to be the framework for public health guidelines developed to lower the incidence of adult hypertension.