Roger R. Williams

Molecular basis of human hypertension: Role of angiotensinogen

Essential hypertension is a common human disease believed to result from the interplay of multiple genetic and environmental determinants. In genetic studies of two large panels of hypertensive sibships from widely separated geographical areas, we obtained evidence of genetic linkage between the angiotensinogen gene (AGT) and hypertension, demonstrated association of AGT molecular variants with the disease, and found significant differences in plasma concentrations of angiotensinogen among hypertensive subjects with different AGT genotypes. The corroboration and replication afforded by these results support the interpretation that molecular variants of AGT constitute inherited predispositions to essential hypertension in humans.

Diagnosing heterozygous familial hypercholesterolemia using new practical criteria validated by molecular genetics

Heterozygous familial hypercholesterolemia (FH) is a serious disorder causing twice normal low-density lipoprotein cholesterol levels early in childhood and very early coronary disease in both men and women. Treatment with multiple medications and diet can normalize cholesterol levels in many persons with FH and prevent or delay the development of coronary atherosclerosis. Thus, there is a need for accurate and genetically validated criteria for the early diagnosis of heterozygous FH. Previously published blood cholesterol criteria greatly underdiagnosed new cases of FH among members of known families with FH in Utah and overdiagnosed FH among participants of general population screening, revealing the need for different cholesterol screening criteria in persons from these 2 different settings. The statistical concept of a priori probabilities was applied to derive 2 sets of practical screening criteria: one for persons participating in general population screening studies and another for close relatives of confirmed FH cases, showing dramatic differences. At a cholesterol level of 310 mg/dl, only 4% of persons in the general population would have FH but 95% of persons who were first-degree relatives of known cases would have FH. Detailed tables were derived to provide practical total and low-density lipoprotein blood cholesterol screening criteria for diagnosing FH in different screening settings and specific age groups. In population screening the new FH criteria require a total cholesterol > 360 mg/dl for age 40+ (or 270 mg/dl in youth). Among first-degree relatives of confirmed cases in families with FH, the new total cholesterol criteria are much lower (> 290 mg/dl for age 40+, > 220 mg/dl for youth).(ABSTRACT TRUNCATED AT 250 WORDS)

Higher Serum Bilirubin Is Associated With Decreased Risk for Early Familial Coronary Artery Disease

Mildly increased serum bilirubin has recently been suggested as a protective factor, possibly reducing the risk of coronary artery disease (CAD) by acting as an antioxidant. We tested this hypothesis by examining serum bilirubin concentrations and other coronary risk factors in 120 men and 41 women with early familial CAD and 155 control subjects. At screening, both cases and control subjects were 38 to 68 years old. Early familial CAD patients had experienced myocardial infarction, coronary artery bypass grafting, or coronary angioplasty by age 55 years for men and 65 for women and had another sibling similarly affected. The average total serum bilirubin concentration was 8.9 +/- 6.1 mumol/L in cases and 12.4 +/- 8.1 mumol/L in control subjects (P = .0001 for difference). In univariate analysis stratified by sex, serum bilirubin was strongly and inversely related to CAD risk, with relative odds of 0.4 to 0.1 (relative to the lowest quintile, P = .04 to .00001) in both men and women as bilirubin increased into the upper two quintiles. Multiple logistic regression analysis was performed including age, sex, smoking, body mass index, diabetes, hypertension, plasma measured LDL cholesterol, HDL cholesterol, triglycerides, and serum bilirubin as potential risk factors. Bilirubin entered as an independent protective factor with an odds ratio of 0.25 (P = .0015) for an increase of 17 mumol/L (1 mg/dL). The standardized logistic regression coefficient for bilirubin was -.33 compared with -.34 for HDL, suggesting that the protective effect of bilirubin on CAD risk in the population is comparable to that of HDL cholesterol. A history of cigarette smoking was associated with significantly lower serum bilirubin concentration and appeared to attenuate the protective effect of bilirubin.

A comparison of positive family history definitions for defining risk of future disease

The relative risk of developing future coronary heart disease (CHD) or hypertension between positive and negative family history families is compared for different definitions of a positive family history when applied to life-table data for 94,292 persons. Having two or more first degree relatives with CHD identifies 8% of the population with relative risks of 3.3-5.9 for CHD before age 50. A quantitative family history score (FHS) compares the familys age and sex specific disease incidence to that expected in the general population and predicts future disease incidence in unaffected family members slightly better (relative risks = 3.4-6.9 for CHD before age 50). Using only one affected relative, even if affected at an early age (less than 55 years old) does not discriminate low and high risk families as well (relative risks = 1.4-3.9 for CHD before age 50). Similar results were obtained for family history of hypertension. There is an increase in future disease incidence for all ages with increasing FHS values (p less than 0.0001), which can be used as a continuous or categorical variable in analysis where family history is associated with a particular variable under study. These results provide a rational basis for choosing and applying specific definitions of a positive family history of coronary disease or hypertension in clinical, epidemiologic and genetic studies.

Genotyping and sequence analysis of apolipoprotein E isoforms

Apolipoprotein E (apoE), a polymorphic plasma protein, is essential for catabolism of lipoproteins by receptor-mediated endocytosis. One of the apoE isoforms (E2) differs in its binding affinity to specific receptors and contributes to variations in lipoprotein metabolism. Diagnosis of apoE isoforms is done by isoelectric focusing, but it is hindered by various degrees of post-translational sialylation of the apoE protein. Electrophoretically silent structural variations may also escape detection by this technique. We describe a method for genotyping apoE based on hybridization of allele-specific oligonucleotides with enzymatically amplified genomic DNA, which permits unambiguous diagnosis of six common apoE phenotypes within 24 h. Among 100 E2 alleles present in 81 unrelated individuals genotyped by this technique, we found two rare structural mutants of apoE in addition to the common E2 form, E2(158Arg----Cys). Automated sequencing of amplified DNA identified the rare mutants as E2(136Arg----Ser) and E2(145Arg----Cys). The genotypic method may complement or even replace isoelectric focusing for routine determination of apoE phenotypes and for identification of rare structural variants.

Usefulness of cardiovascular family history data for population-based preventive medicine and medical research (The Health Family Tree Study and the NHLBI Family Heart Study) ☆

Detailed medical family history data have been proposed to be effective in identifying high-risk families for targeted intervention. With use of a validated and standardized quantitative family risk score (FRS), the degree of familial aggregation of coronary heart disease (CHD), stroke, hypertension, and diabetes was obtained from 122,155 Utah families and 6,578 Texas families in the large, population-based Health Family Tree Study, and 1,442 families in the NHLBI Family Heart Study in Massachusetts, Minnesota, North Carolina, and Utah. Utah families with a positive family history of CHD (FRS > or =0.5) represented only 14% of the general population but accounted for 72% of persons with early CHD (men before age 55 years, women before age 65 years) and 48% of CHD at all ages. For strokes, 11% of families with FRS > or =0.5 accounted for 86% of early strokes (<75 years) and 68% of all strokes. Analyses of >5,000 families sampled each year in Utah for 14 years demonstrated a gradual decrease in the frequency of a strong positive family history of CHD (-26%/decade) and stroke (-15%/decade) that paralleled a decrease in incidence rates (r = 0.86, p <0.001 for CHD; r = 0.66, p <0.01 for stroke). Because of the collaboration of schools, health departments, and medical schools, the Health Family Tree Study proved to be a highly cost-efficient method for identifying 17,064 CHD-prone families and 13,106 stroke-prone families (at a cost of about

Angiotensinogen Genotype, Sodium Reduction, Weight Loss, and Prevention of Hypertension: Trials of Hypertension Prevention, Phase II

27 per high-risk family) in whom well-established preventive measures can be encouraged. We conclude that most early cardiovascular events in a population occur in families with a positive family history of cardiovascular disease. Family history collection is a validated and relatively inexpensive tool for family-based preventive medicine and medical research.

Post-methionine load hyperhomocysteinemia in persons with normal fasting total plasma homocysteine: initial results from The NHLBI Family Heart Study

The angiotensinogen gene has been linked to essential hypertension and increased blood pressure. A functional variant believed to be responsible for hypertension susceptibility occurs at position -6 in the promoter region of the gene in which an A for G base pair substitution is associated with higher angiotensinogen levels. To test whether an allele within the angiotensinogen gene is related to subsequent incidence of hypertension and blood pressure response to sustained sodium reduction, 1509 white male and female subjects participating in phase II of the Trials of Hypertension Prevention were genotyped at the angiotensinogen locus. Participants had diastolic blood pressures between 83 and 89 mm Hg and were randomized in a 2x2 factorial design to sodium reduction, weight loss, combined intervention, or usual care groups. Persons in the usual care group with the AA genotype at nucleotide position -6 had a higher 3-year incidence rate of hypertension (44.6%) compared with those with the GG genotype (31.5%), with a relative risk of 1.4 (95% confidence interval [0.87, 2.34], test for trend across all 3 genotypes, P=0.10). In contrast, the incidence of hypertension was significantly lower after sodium reduction for persons with the AA genotype (relative risk=0.57 [0.34, 0.98] versus usual care) but not for persons with the GG genotype (relative risk=1.2 [0.79, 1.81], test for trend P=0.02). Decreases of diastolic blood pressure at 36 months in the sodium reduction group versus usual care showed a significant trend across all 3 genotypes (P=0.01), with greater net blood pressure reduction in those with the AA genotype (-2.2 mm Hg) than those with the GG genotype (+1.1 mm Hg). A similar trend across the 3 genotypes for net systolic blood pressure reduction (-2.7 for AA versus -0.2 mm Hg for GG) was not significant (P=0.17). Trends across genotypes for the effects of weight loss on hypertension incidence and decreases in blood pressure were similar to those for sodium reduction. We conclude that the angiotensinogen genotype may affect blood pressure response to sodium or weight reduction and the development of hypertension.

A gene for high urinary kallikrein may protect against hypertension in Utah kindreds.

Hyperhomocysteimia, either fasting or after oral methionine loading, appears to be an independent risk factor for coronary heart disease (CHD). It remains unclear whether fasting total homocysteine determination alone adequately detects the full spectrum of hyperhomocysteinemic individuals. We measured fasting and 4-h post methionine loading (0.1 g L-methionine/kg body weight) total plasma homocysteine in 274 participants in The NHLBI Family Heart Study, a population-based investigation of genetic and non-genetic determinants of CHD. Of the total number (n = 47) of hyperhomocysteinemic persons, 43% (20/47) were identified only by methionine loading, while 32% (15/47) of the total number, and 75% of those with post-methionine loading hyperhomocysteinemia only (15/20), had fasting total homocysteine concentrations below the 75th percentile (10.7 mumol/l). We conclude that fasting total plasma homocysteine determination alone fails to identify a sizable percentage (> 40%) of persons who may have clinically relevant hyperhomocysteinemia post methionine loading.

Blunted renal vascular response to angiotensin II is associated with a common variant of the angiotensinogen gene and obesity.

The inheritance of 12-hour overnight total urinary kallikrein excretion and its association with family history of essential hypertension were studied in 405 normotensive adults and 391 youths in 57 Utah pedigrees. Total urinary kallikrein excretion was highly familial with 51% of the total variance attributable to a dominant allele for high total urinary kallikrein excretion and 27% attributable to the combined effects of polygenes and shared family environment. An estimated 28% of the population has one or two copies of the dominant allele for high total urinary kallikrein excretion (2.3 SD units higher than the low homozygotes). About 83% of the population could be assigned to one of the two genotypic populations. Individuals with the high total urinary kallikrein excretion genotype were significantly less likely to have one or two hypertensive parents (relative odds = 0.56, p = 0.042). We conclude that a dominant allele expressed as high total urinary kallikrein excretion may be associated with decreased risk of essential hypertension. Further studies should be performed to confirm this finding and to test for interactions between this apparently protective gene and other genetic and environmental determinants of essential hypertension.