NHLBI Family Heart Study Research Articles

Evidence for a major gene accounting for mild elevation in LDL cholesterol: the NHLBI Family Heart Study.

Studies of rare Mendelian disorders of low density lipoprotein cholesterol (LDL-C) metabolism have identified specific genetic mutations in the LDL receptor and apolipoprotein B. Although these rare mutations account for a small proportion of LDL-C variation, twin and adoption studies indicate that at least 50% of the overall LDL-C observed variation is genetically determined. In a heterogeneous sample of 3227 subjects from the NHLBI Family Heart Study collected from four US centres, we find evidence for a common major gene accounting for mild elevations (1.25 standard deviations) in LDL-C. The analysis favored a recessive model with a frequency of 0.52 for the gene influencing elevated LDL-C, phenotypic means of 113 mg/dl for the normal genotypes and 146 mg/dl for the abnormal genotype, and a significant polygenic heritability. This statistically-inferred major gene accounted for 24% of the variation in LDL-C, with polygenes accounting for another 28% of the variation. Using parameters for major gene transmission estimated in the segregation analysis, LDL-C showed no linkage to the LDL receptor gene (LDLR), nor to the apolipoprotein E gene (APOE), nor to the cholesterol 7alpha-hydroxylase gene (CYP7A1), indicating the major gene effect influencing mild elevation in LDL-C is not explained by any of these candidate loci.

A frailty approach for modelling diseases with variable age of onset in families: the NHLBI Family Heart Study.

We use frailty models to analyse the effect of latent genetic and environmental risk factors on hazard functions in nuclear families. The approach expresses latent risk factors (frailties) as functions of the effects of a single major gene and shared familial risk. The latter may result from shared polygenes and/or a common environment. Genetic frailties are modelled using a two-point distribution, and residual frailties (shared environment, polygenes) using a gamma distribution. The two-point distribution follows the laws of Mendelian transmission, under either dominant or recessive gene action. We describe a robust EM approach for the joint estimation of the magnitude of genetic, covariate, gene by covariate interaction effects while allowing residual familial correlation. We illustrate the method on coronary heart disease data from the National Heart, Lung, and Blood Institute Family Heart Study. In addition, a simulation study shows that ignoring possible residual correlation in disease status due to a shared familial environment leads to an overestimate of the relative risk associated with a latent genotype.

Lewis blood group phenotype as an independent risk factor for coronary heart disease (the NHLBI Family Heart Study)

In the Copenhagen Male Study, men with Lewis blood group phenotype Le(a−b−) were found to have increased risk for coronary heart disease (CHD); such a relation has not been confirmed in men, and has not been evaluated in women. In the NHLBI Family Heart Study, we determined the Lewis blood type of 1,620 white subjects (790 male and 830 female subjects). The Lewis(a−b−) phenotype was found in 142 subjects (8.8%), 6.3% of subjects from randomly chosen families and 9.7% of subjects from families found to be at high risk for CHD. A history of CHD was present in 39.1% of men with Le(a−b−) versus 27.2% of men with other Lewis types; for women, the corresponding numbers were 12.3% versus 9.4%, respectively. In multivariate analysis, adjusting for age, sex, and risk group, the odds ratio for CHD was 2.0 (95% confidecne interval = 1.2 to 3.1) for Le(a−b−) versus other Lewis groups. Mean values for body mass index, blood pressure, total cholesterol, low-density lipoprotein and high-density lipoprotein cholesterol, glucose, insulin, homocysteine, and fibrinogen were not significantly different between Le(a−b−) subjects and others, but triglycerides (p = 0.002) were higher in the Le(a−b−) subjects. However, inclusion of all risk factors in multivariate analysis did not diminish the increased risk for CHD associated with the Le(a−b−) phenotype. We conclude that the Le(a−b−) phenotype is associated with an increased risk for CHD; its effect does not appear to act predominantly through conventional cardiovascular risk factors. At present, mechanisms of effect are unknown.

Accuracy of proband reported family history: the NHLBI Family Heart Study (FHS).

Proband-reported family histories are widely used in research and counseling, yet little is known about the validity of family history reporting. The Family Heart Study (FHS), a population-based study of familial cardiovascular disease, gathered family history information from 3,020 middle-aged probands in four U.S. communities. Probands reported on the history of coronary heart disease (CHD), diabetes, hypertension, and asthma among a total of 10,316 living relatives (9,186 siblings, 1,130 parents) and 2,685 spouses. Questionnaires were returned by 6,672 siblings, 901 parents, and 2,347 spouses, yielding response rates of 73, 79, and 87%, respectively. Utilizing the relatives' self-report as the standard, sensitivity of the proband report on their spouse, parent, and sibling was 87, 85, and 81% for CHD, 83, 87, and 72% for diabetes, 77, 76, and 56% for hypertension, and 66, 53, and 39% for asthma, respectively. Most specificity values were above 90%. Analyses using generalized estimating equations (GEE) were performed to evaluate differences in proband accuracy based on the proband's age, gender, disease state, center, and ethnicity. In multivariate models, age, gender, and disease status were significantly associated with the accuracy of proband's report of sibling disease history, but had little effect on the accuracy of their report on spouses or parents. In general, older probands were significantly less accurate reporters of disease than younger probands. These results demonstrate that CHD family history can be captured effectively based on proband reports, but suggest that additional family contacts may be helpful when working with older probands or with chronic diseases that have few recognized medical events or procedures.

Lipoprotein(a) interactions with lipid and non-lipid risk factors in patients with early onset coronary artery disease: Results from the NHLBI Family Heart Study

Background: A positive interaction between high plasma lipoprotein(a) [Lp(a)] and unfavorable plasma lipid levels has been reported to result in very high risk for premature coronary artery disease (CAD). We further examined this issue for men and women with early onset CAD. We also examined potential interactions between Lp(a) and non-lipid risk factors. Methods and results: In 338 men and women with early onset CAD (most with a positive family history of early CAD) and 480 general population controls, we measured Lp(a), lipids and other risk factors. In univariate analysis, relative odds for CAD was 1.7 ( P=0.002) for plasma Lp(a)>50 mg/dl. Elevated Lp(a) level was found to interact with adjusted plasma total/high density lipoprotein (HDL) cholesterol such that when Lp(a) was over 50 mg/dl and adjusted plasma total/HDL cholesterol>5.8, relative odds for CAD were 8.0–9.6 ( P<0.0001) in multiple logistic regression. Non-lipid risk factors were generally found to multiply the risk associated with Lp(a) (as predicted by logistic regression) without evidence for interaction. Conclusions: We find evidence that Lp(a) does interact positively with adjusted plasma total/HDL cholesterol ratio. Aggressive risk factor intervention, especially for lipids, in those with elevated Lp(a) therefore appears indicated.

288 Hostility, social support and CHD in the NHLBI family heart study

288 Hostility, social support and CHD in the NHLBI family heart study

No Association between Factor V Leiden Mutation and Coronary Heart Disease or Carotid Intima Media Thickness: The NHLBI Family Heart Study

No Association between Factor V Leiden Mutation and Coronary Heart Disease or Carotid Intima Media Thickness: The NHLBI Family Heart Study

Associations of candidate loci angiotensinogen and angiotensin-converting enzyme with severe hypertension: The NHLBI family heart study

PURPOSE: In studies conducted in several different populations, the M235T substitution in the antiotensinogen (AGT) locus has been associated with hypertension. METHODS: A case-control study was initiated in an attempt to replicate this finding. Persons with hypertension, age- and sex-matched normotensive controls, and randomly sampled individuals were probands from the Family Heart Study of the National Heart, Lung, and Blood Institute. Subjects were recruited from the Atherosclerosis Risk in Communities study (ARIC) in North Carolina and Minneapolis, MN, and from the Framingham Heart Study in Massachusetts. Genotypes were determined for the M235T substitution in the AGT locus and for the insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) locus. Simple association tests as well as logistic regression analyses were performed. RESULTS: The association of AGT-T235 with hypertension was replicated in the Framingham sample (odds ratio, 1.60; 95% confidence interval, 1.11–2.30), but not in the ARIC white or black subjects. However, logistic regression analysis suggested a significant association of AGT with hypertension in both the ARIC white and Framingham samples when the effects of body mass index, triglycerides, and the presence of significant coronary heart disease were controlled. These analyses further suggested that, in the ARIC data, the relationship with the AGT locus is stronger in women than men and that there may be interaction (epistasis) between homozygotes for T235 and ACE-DD in the Framingham data. While the small sample size precluded logistic regression analysis, the frequency of the T235 allele in the black random sample was much higher than in the comparable white sample. CONCLUSIONS: These results are compatible with the presence of a genetic risk factor for hypertension in or near the angiotensinogen locus.

NHLBI Family Heart Study: objectives and design.

The NHLBI Family Heart Study is a multicenter, population-based study of genetic and nongenetic determinants of coronary heart disease (CHD), atherosclerosis, and cardiovascular risk factors. In phase I, 2,000 randomly selected participants and 2,000 with family histories of CHD were identified among 14,592 middle-aged participants in epidemiologic studies. Medical histories from these individuals, their parents, and their siblings were used to calculate family risk scores that compared the number of reported and validated CHD events with the number expected based on the size, sex, and age of family members. A total of 657 families with the highest risk scores and early-onset CHD and 588 randomly sampled families had clinic examinations that included electrocardiograms, carotid artery ultrasound scans, spirometry, measurements of body size, blood pressure, lipids, lipoproteins, hemostatic factors, insulin, glucose, and routine chemistries. Additional biochemical and genetic studies are being performed on selected participants. Serum, plasma, lymphocytes, red cells, and DNA are stored for future studies, including genotyping of candidate genes and anonymous markers. Contributions of genes, shared and individual environments, and behaviors to variations in risk factors, preclinical atherosclerosis, and CHD will be estimated. Linkage studies, including the quantitative trait loci approach, are planned.

Relation Between Folate Status, a Common Mutation in Methylenetetrahydrofolate Reductase, and Plasma Homocysteine Concentrations

Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5-methyltetrahydrofolate, the major carbon donor in remethylation of homocysteine to methionine. A common MTHFR mutation, an alanine-to-valine substitution, renders the enzyme thermolabile and may cause elevated plasma levels of the amino acid homocysteine. To assess the potential interaction between this mutation and vitamin coenzymes in homocysteine metabolism, we screened 365 individuals from the NHLBI Family Heart Study. Among individuals with lower plasma folate concentrations ( < 15.4 nmol/L), those with the homozygous mutant genotype had total fasting homocysteine levels that were 24% greater (P<.05) than individuals with the normal genotype. A difference between genotypes was not seen among individuals with folate levels > or = 15.4 nmol/L. Individuals with thermolabile MTHFR may have a higher folate requirement for regulation of plasma homocysteine concentrations; folate supplementation may be necessary to prevent fasting hyperhomocysteinemia in such persons.

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

Hyperhomocysteinemia, 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 μmol/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.