PROJECT 3: Genetic epidemiology of cardiovascular disease and healthy aging

Stephen Fortmann MD, Principal Investigator

Cardiovascular disease (CVD) is one of the most complex and multifactorial diseases known. The major determinants of CVD incidence in a population are environmental and behavioral - dietary composition, tobacco smoking, physical activity levels - operating on individuals with a common, but complex, genetic milieu that imparts broad susceptibility to these environmental risk factors.

Exposure to these risk factors produces quite different effects in different individuals, ranging from few important changes to markedly unhealthy lipoprotein levels, high blood pressure, insulin resistance, diabetes, obesity, etc. A fundamental feature of CVD is the complex, quantitative interaction of behavior, environment, and genetics to determine the type, degree, and timing of clinical manifestations. Some individuals devel op CVD without manifesting very extreme levels of any of the classical risk factors while other individuals remain free of disease for very long periods despite exposure to several risk factors. This heterogeneity is likely due to newer, less-well-studied risk factors and protective behaviors, and to fundamental genetic susceptibility. Project 3 will include studies of all of these factors. The prevention of cardiovascular disease will therefore benefit from a better understanding of the genetic risk factors for CVD, both t o improve the prediction of individual risk, allowing better tailoring of preventive therapy, and to open novel aven ues for primary and secondary prevention.

The specific aims of Project 3 include establishing three cohorts of participants: younger cases of atherosclerotic CVD, younger controls without CVD, and older controls without CVD or other chronic diseases. The younger cases and controls will be aged 30-45 (men) or 55 (women) and the older controls will be aged 60-69. Younger cases will have had MI due to atherosclerosis or angina diagnosed with positive angiography (at least one stenosis exceeding 50%). Cases and controls will be assessed for conventional and newer CVD risk factors. Older controls will also be assessed for subclinical CVD by high-speed multi-detector row spiral computed tomography, ankle and brachial blood pressures, and endothelial function. Older controls will be reassessed two years after the baseline visit.
Cross-sectional and longitudinal studies of all groups will explore the inter-relationships of subclinical disease, and both clinical and subclinical disease progression, to the various risk factors assessed. We will compare the prevalence of polymorphisms in the older controls and younger cases, seeking to maximize the likelihood of genetic differences. However, the age difference between these two groups make other contrasts difficult to interpret. Therefore, we will use older cases from Project 4 and the young controls from Project 3 to explore robust models of gene-disease, gene-gene, and gene-environment interactions and associations.

Specific Aims

1 . Recruit and characterize 700 cases with early-onset CVD

. Recruit men and women with documented MI, or angina pectoris accompanied by a positive coronary angiogram, with onset before age 45 (men) or 55 (women).
. Characteri ze the cases for important covariates for the genetic studies: medical history, current therapy, exercise levels, diet, standard risk factors, and measures of insulin resistance (fasting glucose, insulin) and inflammation (C-reactive protein).
. Characterize in cases newer risk factors of interest: lipoprotein (a), homocysteine, folate, a coagulation measure (probably D-dimer), and asymmetric dimethyl arginine (ADMA)
. Characterize peripheral vascular disease in these young cases using ankle-brachial index (ABI).
. Measure psychosocial factors in these cases.
. Obtain DNA from all confirmed cases for genetic analysis.

2 . Recruit and characterize ~300 age-matched controls without clinical CVD

. Recruit men and women aged ~30-45(men)/55 (women) with no history of CVD in their diagnosis lists, confirmed by interview.
. Characterize the controls for important covariates for the genetic studies: as for cases.
. Characterize in controls newer risk factors of interest: as for cases.
. Obtain DNA from all controls for genetic analysis.
. Characterize peripheral vascular disease in these young controls using ankle-brachial index (ABI)
. Measure psychosocial factors in the controls.

3. Develop a collaboration with CARDIA to identify ~400 additional young controls

. Obtain risk factor data from the Oakland CARDIA cohort database.
. Obtain DNA from stored cells for genetic analyses.

4. Recruit and characterize 1200 older controls without clinical CVD

. Recruit men and women aged 60-69 with no history of CVD, cancer (except non-melanoma skin cancer), liver cirrhosis, renal failure, HIV/AIDS, or dementia in their diagnosis lists, confirmed by interview.
. Characterize the controls for important covariates for the genetic studies: as for cases.
. Characterize in controls newer risk factors of interest: as for cases.
. Obtain DNA from all controls for genetic analysis.
. Characterize subclinical peripheral vascular disease in all controls using ankle-brachial index (ABI) and subclinical coronary disease using multi-detector row computed tomography measurement of coronary artery calcification (CAC).
. Measure psychosocial factors, autonomic function (heart rate variability), and endothelial function in the controls.
. Follow all controls for the progression of subclinical disease by repeat CAC and ABI after 24 months.
. Explore factors, genetic and environmental, that are associated with health in this group.

5. Follow all participants for the development or recurrence of clinical CVD; store frozen plasma at - 80° C for future studies.

Overview of the Design of Project 3

The original design for Project 3 deliberately included only younger cases and older controls to maximize the phenotypic difference and to select a case group that is likely rich in genetically-based disease (we are also interested in the older controls as a separate group). While some gene-environment interaction analysis would be possible within these two groups, and between them for non-age-related variables, more robust analyses are possible with an age-matched control group. In addition, we decided that Project 4 could be conducted in such a way as to allow selection of a group of older cases matched in age to the older controls in Project 3. A fully-symmetrical design is thus possible by adding a younger control group, which was feasible by developing a collaboration with the NIH CARDIA Study, being conducted in part at Kaiser Permanente Division of Research (KPDOR).

To summarize, our revised overall design provides for the following study groups from Projects 3 and 4 for the study of gene association with atherosclerosis:

This design will allow modeling of genetic and environmental variables across all four groups. Since Project 4 will include 1000 cases of MI and 1000 cases of angina, for this study of atherosclerosis we will be able to include either type of case, providing the age criterion (60-69) is met. This design requires that we collect data as similarly as possible in both Projects 3 and 4, and comparably to CARDIA, which is how we implemented the study.