Franklyn I Bennett

The prevalence of hypertension in seven populations of west African origin.

OBJECTIVES This study was undertaken to describe the distribution of blood pressures, hypertension prevalence, and associated risk factors among seven populations of West African origin. METHODS The rates of hypertension in West Africa (Nigeria and Cameroon), the Caribbean (Jamaica, St. Lucia, Barbados), and the United States (metropolitan Chicago, Illinois) were compared on the basis of a highly standardized collaborative protocol. After researchers were given central training in survey methods, population-based samples of 800 to 2500 adults over the age of 25 were examined in seven sites, yielding a total sample of 10014. RESULTS A consistent gradient of hypertension prevalence was observed, rising from 16% in West Africa to 26% in the Caribbean and 33% in the United States. Mean blood pressures were similar among persons aged 25 to 34, while the increase in hypertension prevalence with age was twice as steep in the United States as in Africa. Environmental factors, most notably obesity and the intake of sodium and potassium, varied consistently with disease prevalence across regions. CONCLUSION The findings demonstrate the determining role of social conditions in the evolution of hypertension risk in these populations.

Genome-Wide Association Study of Coronary Heart Disease and Its Risk Factors in 8,090 African Americans: The NHLBI CARe Project

Coronary heart disease (CHD) is the leading cause of mortality in African Americans. To identify common genetic polymorphisms associated with CHD and its risk factors (LDL- and HDL-cholesterol (LDL-C and HDL-C), hypertension, smoking, and type-2 diabetes) in individuals of African ancestry, we performed a genome-wide association study (GWAS) in 8,090 African Americans from five population-based cohorts. We replicated 17 loci previously associated with CHD or its risk factors in Caucasians. For five of these regions (CHD: CDKN2A/CDKN2B; HDL-C: FADS1-3, PLTP, LPL, and ABCA1), we could leverage the distinct linkage disequilibrium (LD) patterns in African Americans to identify DNA polymorphisms more strongly associated with the phenotypes than the previously reported index SNPs found in Caucasian populations. We also developed a new approach for association testing in admixed populations that uses allelic and local ancestry variation. Using this method, we discovered several loci that would have been missed using the basic allelic and global ancestry information only. Our conclusions suggest that no major loci uniquely explain the high prevalence of CHD in African Americans. Our project has developed resources and methods that address both admixture- and SNP-association to maximize power for genetic discovery in even larger African-American consortia.

Fetal growth and cardiovascular risk factors in Jamaican schoolchildren

Abstract Objective: To determine relation between schoolchildrens blood pressure, glycated haemoglobin level, and cholesterol concentration and their anthropometry, socioeconomic status, and birth measurements. Design: Retrospective cohort study. Setting: 27 schools closest to University Hospital of the West Indies, Kingston, Jamaica. Subjects: 2337 children aged 6-16 years who were born at university hospital were recruited, and their birth records were recovered: 1610 had suitable records, 659 had records including birth length, and 610 of these were prepubertal. Main outcome measures: Blood pressure, glycated haemoglobin level, serum cholesterol concentration, anthropometry at birth, current anthropometry, and socioeconomic status. Results: Multiple regression analysis showed that childrens systolic blood pressure was inversely related to their birth weight (P<0.0001) and directly related to their current weight. Glycated haemoglobin level was higher in children with thicker triceps skinfolds (P<0.001) and who had been shorter at birth (P=0.003). Serum cholesterol concentration was inversely related to current height (P=0.001) and to length at birth (P=0.09) and was directly related to triceps skinfold thickness and higher socioeconomic status (P<0.001). Conclusions: Blood pressure in childhood was inversely related to birth weight and directly to current weight. Glycaemic control and serum cholesterol were related to short length at birth, height deficit in childhood, and childhood obesity.

ACE, angiotensinogen and obesity: a potential pathway leading to hypertension.

The renin-angiotensin system (RAS) plays a crucial role in the regulation of fluid volume, thereby influencing blood pressure (BP). Obesity is an important risk factor for hypertension, however the physiologic basis for this relationship has not been clarified. In a population survey we examined the potential relationship between the RAS and obesity. Based on community sampling, 449 individuals were recruited from metropolitan Kingston, Jamaica. Serum angiotensin-converting enzyme (ACE) and circulating angiotensinogen levels were measured and the associated genes were typed for previously described polymorphisms. Obese individuals (body mass index >31) had significantly higher serum ACE and angiotensinogen levels, this relationship persisted for ACE in multivariate analyses controlling for BP, hypertension status, age, and gender. The insertion/deletion polymorphism of the ACE gene was associated with variation in the levels of ACE, but inconsistently with body mass index. Variants of the angiotensinogen gene leading to amino acid substitutions at positions 174 and 235 did not influence levels either of angiotensinogen or obesity. These data suggest that obesity may alter the levels of ACE and angiotensinogen, and provide a potential pathway through which obesity leads to elevation of BP.

Fetal growth is directly related to maternal anthropometry and placental volume

Objective: To describe the influence of maternal weight and weight gain, placental volume and the rate of placental growth in early pregnancy on fetal dimensions measured sonographically.Design: In a prospective study, 712 women were recruited from the antenatal clinic of the University Hospital of the West Indies. Data analysis was confined to 374 women on whom measurements of the placental volume at 14, 17 and 20 weeks gestation were complete. Measurements of maternal anthropometry and fetal size (by ultrasound) were performed. Weight gain in pregnancy between the first antenatal visit (8–10 weeks) and 20 weeks gestation, and the rate of growth of the placenta between 14–17 and 17–20 weeks gestation were calculated.Main outcome measures: Fetal anthropometry (abdominal and head circumferences, femoral length, and biparietal diameter) at 35 weeks gestation.Results: Lower maternal weight at the first antenatal visit was associated with a significantly smaller placental volume at 17 and 20 weeks gestation (P<0.002 and <0.0001 respectively). In all women, maternal weight gain was directly related to fetal anthropometry. Placental volume at 14 weeks gestation and the rate of growth of the placenta between 17 and 20 weeks gestation were significantly related to all four fetal measurements.Conclusion: This study has provided evidence that both placental volume, and the rate of placental growth may influence fetal size. These effects are evident in the first half of pregnancy, and appear to be mediated through maternal weight and weight gain.Sponsorship: This study was supported by a grant from the Wellcome Trust, 183 Euston Road, London, England.

Blood Pressure Is Related to Placental Volume and Birth Weight

The objective of this study was to determine whether maternal nutrition and fetal and placental size program blood pressure. A longitudinal study linking the maternal anthropometric measurements of the first antenatal visit, ultrasound data of placental and fetal size, anthropometry at birth, and childhood growth and blood pressure was performed. The subjects were 428 women who attended the antenatal clinic at the University Hospital of the West Indies, Kingston, Jamaica, and their children, who were subsequently followed up. Systolic blood pressure at ages 1, 2, 2.5, 3, and 3.5 years was the main outcome measure. Pooling the data across ages, systolic blood pressure fell by 1.4 mm Hg for every 1-kg increase in birth weight (95% CI 0.2 to 2.7, P=0.02) and by 1.2 mm Hg for every 100-mL increase in placental volume at 20 weeks of gestation (95% CI 0.4 to 2.0, P=0.004). Blood pressure was also negatively associated with placental volume at 17 weeks and fetal abdominal circumference at 20 weeks. Measures of maternal nutritional status were strongly related to birth weight and placental volume but not directly to childhood blood pressure at these young ages. In conclusion, blood pressure is associated with fetal size in this population, as previously described among Europeans. We found associations between placental volume and abdominal circumference in the second trimester and childhood blood pressure, suggesting that the initiating events of blood pressure programming occur early in pregnancy. Measures of maternal nutritional status were not directly related to childhood blood pressure at these young ages but were strong predictors of both birth weight and placental volume, suggesting an indirect relation.

Diabetes in the Caribbean: results of a population survey from Spanish Town, Jamaica.

Aims To characterize the prevalence of diabetes and associated risk attributes in the Jamaican population.

Admixture and Population Stratification in African Caribbean Populations

Throughout biomedical research, there is growing interest in the use of ancestry informative markers (AIMs) to deconstruct racial categories into useful variables. Studies on recently admixed populations have shown significant population substructure due to differences in individual ancestry; however, few studies have examined Caribbean populations. Here we used a panel of 28 AIMs to examine the genetic ancestry of 298 individuals of African descent from the Caribbean islands of Jamaica, St. Thomas and Barbados. Differences in global admixture were observed, with Barbados having the highest level of West African ancestry (89.6%± 2.0) and the lowest levels of European (10.2%± 2.2) and Native American ancestry (0.2%± 2.0), while Jamaica possessed the highest levels of European (12.4%± 3.5) and Native American ancestry (3.2%± 3.1). St. Thomas, USVI had ancestry levels quite similar to African Americans in continental U.S. (86.8%± 2.2 West African, 10.6%± 2.3 European, and 2.6%± 2.1 Native American). Significant substructure was observed in the islands of Jamaica and St. Thomas but not Barbados (K=1), indicating that differences in population substructure exist across these three Caribbean islands. These differences likely stem from diverse colonial and historical experiences, and subsequent evolutionary processes. Most importantly, these differences may have significant ramifications for case‐control studies of complex disease in Caribbean populations.

The effects of birth weight and postnatal linear growth retardation on blood pressure at age 11–12 years

STUDY OBJECTIVE To determine the effects of birth weight and linear growth retardation (stunting) in early childhood on blood pressure at age 11–12 years. DESIGN Prospective cohort study. SETTING Kingston, Jamaica. PARTICIPANTS 112 stunted children (height for age < −2 SD of the NCHS references) and 189 non-stunted children (height for age > −1 SD), identified at age 9–24 months by a survey of poor neighbourhoods in Kingston. MAIN RESULTS Current weight was the strongest predictor of systolic blood pressure (β= 4.90 mm Hg/SD weight 95%CI 3.97, 5.83). Birth weight predicted systolic blood pressure (β = −1.28 mm Hg/SD change in birth weight, 95% CI −2.17, −0.38) after adjustment for current weight. There was a significant negative interaction between stunting in early childhood and current weight indicating a larger effect of increased current weight in children who experienced linear growth retardation in early childhood. There was no interaction between birth weight and current weight. The increase in blood pressure from age 7 to age 11–12 was greater in children with higher weight at age 11–12 and less in children with higher birth weight and weight at age 7. CONCLUSIONS Birth weight predicted systolic blood pressure in Jamaican children aged 11–12. Postnatal growth retardation may potentiate the relation between current weight and blood pressure. Greater weight gain between ages 7 and 11 was associated with a greater increase in systolic blood pressure. The relation between growth and later blood pressure is complex and has prenatal and postnatal components.

The angiotensin converting enzyme and blood pressure in Jamaicans.

An insertion/deletion (I/D) polymorphism of the angiotensin I converting enzyme gene influences the level of serum angiotensin converting enzyme activity and has been associated with risk of several cardiovascular conditions. The relationship to blood pressure remains uncertain, however. We conducted a population-based survey in Kingston, Jamaica, to examine the association between angiotensin converting enzyme genotype, angiotensin converting enzyme serum activity and blood pressure. Serum angiotensin converting enzyme activity was measured and genotyping performed for the I/D polymorphism in 500 community residents. The overall prevalence of the D allele was 59.3%. Angiotensin converting enzyme genotype was not significantly related to blood pressure (P = .16), although it did influence angiotensin-converting enzyme activity, leading to an increase of 35% among individuals with the DD as compared with II genotype. Angiotensin converting enzyme levels were significantly higher in hypertensives as compared with normotensives (P < .05). A modest correlation was observed between blood pressure and angiotensin converting enzyme activity among untreated individuals (r = 0.11; P = .04), although this did not persist in multivariate analysis. A relationship between body mass index and angiotensin converting enzyme activity was identified in both men and women that was independent of genotype. These data demonstrate findings among blacks which are consistent with other studies and suggest a relationship between angiotensin converting enzyme genotype, and serum activity which is influenced by both genetic and environmental factors. The potential role of ACE on blood pressure control in the population remains uncertain.