Rainford J Wilks

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.

Prevalence of NIDDM Among Populations of the African Diaspora

OBJECTIVE Rates of non-insulin-dependent diabetes mellitus have risen sharply in recent years among blacks in the U.S. and the U.K. Increases in risk have likewise been observed in the island nations of the Caribbean and in urban West Africa. To date, however, no systematic comparison of the geographic variation of NIDDM among black populations has been undertaken. RESEARCH DESIGN AND METHODS In the course of an international collaborative study on cardiovascular disease, we used a standardized protocol to determine the rates of NIDDM and associated risk factors in populations of the African diaspora. Representative samples were drawn from sites in Nigeria, St. Lucia, Barbados, Jamaica, the United States, and the United Kingdom. A total of 4,823 individuals aged 25–74 years were recruited, all sites combined. RESULTS In sharp contrast to a prevalence of 2% in Nigeria, age-adjusted prevalences of self-reported NIDDM were 9% in the Caribbean and 11% in the U.S. and the U.K. Mean BMI ranged from 22 kg/m2 among men in West Africa to 31 kg/m2 in women in the U.S. Disease prevalence across sites was essentially collinear with obesity, pointing to site differences in the balance between energy intake and expenditure as the primary determinant of differential NIDDM risk among these populations. CONCLUSIONS In ethnic groups sharing a common genetic ancestry, these comparative data demonstrate the determining influence of changes in living conditions on the population risk of NIDDM.

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.

Hypertension in four African-origin populations : current 'Rule of Halves', quality of blood pressure control and attributable risk of cardiovascular disease

Objective To assess the public health burden from high blood pressure and the current status of its detection and management in four African-origin populations at emerging or high cardiovascular risk. Design Cross-site comparison using standardized measurement and techniques. Setting Rural and urban Cameroon; Jamaica; Manchester, Britain. Subjects Representative population samples in each setting. African-Caribbeans (80% of Jamaican origin) and a local European sample in Manchester. Main outcome measures Cross-site age-adjusted prevalence; population attributable risk. Results Among 1587 men and 2087 women, age-adjusted rates of blood pressure ⩾ 160 or 95 mmHg or its treatment rose from 5% in rural to 17% in urban Cameroon, despite young mean ages, to 21% in Jamaica and 29% in Caribbeans in Britain. Treatment rates reached 34% in urban Cameroon, and 69% in Jamaican- and British- Caribbean-origin women. Sub-optimal blood pressure control (> 140 and 90 mmHg) on treatment reached 88% in European women. Population attributable risks (or fractions) indicated that up to 22% of premature all-cause, and 45% of stroke mortality could be reduced by appropriate detection and treatment. Additional benefit on just strokes occurring on treatment could be up to 47% (e.g. in both urban Cameroon men and European women) from tighter blood pressure control on therapy. Cheap, effective therapy is available. Conclusion With mortality risk now higher from non-communicable than communicable diseases in sub-Saharan Africa and elsewhere, systematic measurement, detection and genuine control of hypertension once treated can go hand-in-hand with other adult health programmes in primary care. Cost implications are not great. The data from this collaborative study suggest that such efforts should be well rewarded.

Quantitative proviral DNA and antibody levels in the natural history of HTLV-I infection

The pathogenesis of human T-cell lymphotropic virus type I (HTLV-I) in adult T-cell leukemia/lymphoma (ATL) and HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) is poorly understood. We prospectively followed up and evaluated the virologic correlates of infection in transfusion recipients after seroconversion, in asymptomatic carriers, and in ATL and HAM/TSP patients. Proviral DNA levels (copies/105 lymphocytes) were determined by real-time automated polymerase chain reaction and antibody titers by end-point dilution by use of an HTLV-I enzyme-linked immunoassay. In early infection, proviral load was initially elevated (median, 212 copies/105 lymphocytes at time 1) and later decreased (median, 99 copies at time 2, and 27 copies at time 3). Corresponding antibody titers were low at time 1 (1:2154), had significantly increased by time 2 (1:12312), and were stable by time 3 (1:4694). These viral markers were significantly lower in asymptomatic carriers than in HAM/TSP or ATL patients. Therefore, proviral load and antibody titers may be useful as predictive markers of disease among carriers.

Standardization of blood pressure measurement in an international comparative study

In the context of a collaborative study on the epidemiology of hypertension in populations of West African origin procedures for standardization of the measurement of blood pressure were evaluated. Comparisons of mean levels of blood pressure, which in large part determine prevalence rates, are highly sensitive to differences in technique. While rotating a single field team may be the ideal approach to multisite studies, it is not practical in international collaborative research. Appropriate techniques to standardize multiple teams over a long period of time have not been well developed, however. In the present study 8981 individuals were examined in eight sites in six countries with the standard mercury sphygmomanometer. An evaluation of the effectiveness of central training, site visits, monitoring of digit preference, and the use of an electronic device for internal standardization is described. In all but one of the sites reliability was high and comparable to the observers at the Coordinating Center. Digit preference for the entire set of measurements was limited (frequency of terminal zero = 23.5% for systolic and 28.9% for diastolic readings) and could be shown to have virtually no effect on prevalence rates or correlation estimates. Mean differences among observers within a given site and between sites were small (+/- 0-5 mmHg). While logistically complex, these methods can provide the basis for standardization in international comparative blood pressure surveys.

Heritability of obesity-related traits among Nigerians, Jamaicans and US black people.

OBJECTIVE: The mean values for anthropometric traits vary across population groups and this variation is clearly determined for the most part by the environment. The familiarity of anthropometric traits also varies in reports from different populations, although this variation has not been shown to follow a consistent pattern. To examine whether heritability is influenced by socio-cultural factors, we conducted a cross-cultural study of populations of the African diaspora.PARTICIPANTS: Data were collected on 1868 family members from Nigeria, 623 from Jamaica and 2132 from metropolitan Chicago, IL, USA.MEASUREMENTS: Height and weight were measured and body mass index (kg/m2) calculated. Fat-free mass, fat mass and percentage body fat were estimated using bioelectrical impedance analysis. Plasma leptin concentrations were also measured. The proportion of variance attributable to additive genetic and non-shared environmental components was estimated with the maximum likelihood variance decomposition method.RESULTS: Mean values for all anthropometric traits increased along the socio-cultural gradient, and obesity increased from 5% in Nigeria to 23% in Jamaica and 39% in the USA. Within populations the relationships among traits both within individuals and within families were highly consistent. Heritability estimates for weight, body mass index, fat mass and percentage body fat were approximately 50% for all groups. Heritability for height was lower in Nigeria (62%) than in Jamaica (74%) or the US (87%).CONCLUSION: The familial patterns of body size and energy storage appear to be consistent in these genetically related populations across a wide range of environmental conditions.