NIH-Funded Genetic Determinants of PAD

PI: John P. Cooke, MD, PhD
Co-PI: Thomas Quertermous, MD

			Study technician finding absolute claudication time on a treadmill. Determining arterial elasticity with the CV Profiler. Determining endothelial function with flow mediated vasodilatation.

Differences in the level of exposure to traditional risk factors do not provide an adequate explanation for the observation that some patients with atherosclerosis primarily manifest it in the coronary arteries, whereas others manifest the disease in peripheral arteries. Because known systemic risk factors and environmental influences are similar in patients with coronary artery disease (CAD) and those with peripheral arterial disease (PAD), it is likely that unknown environmental and genetic factors are responsible for the individual heterogeneity in plaque distribution. Accordingly, the specific aims of this proposal are to:

• To elucidate genetic determinants which increase the propensity of an individual to develop hemodynamically significant atherosclerosis in the arteries of the lower extremity.

• To examine the interaction of these genetic determinants with known risk factors for atherosclerosis.

We will begin by identifying single nucleotide polymorphisms (SNPs) in candidate genes that are regulated in the vasculature. SNPs will be chosen based on their prevalence, and the location and effect of the SNP on the primary amino acid sequence of the protein. The candidate genes targeted for study will be selected based upon our prior and ongoing work which focuses upon transcriptional profiling of vascular cells exposed to pathophysiologically relevant stimuli, with in vivo confirmation. In parallel, we will undertake a cross-sectional case-control genomic study of two sharply defined clinical phenotypes. Cases will have hemodynamically significant PAD as documented by reduced ABIs. Controls will have similar clinical co-variates (ie. similar risk factor profile) but will not have significant PAD as documented by normal ABIs. Blood will be drawn for genomic DNA, and SNPs detected using high throughput Taqman analysis. Data will be gathered on other clinical covariates (eg. blood pressure, tobacco exposure, and plasma levels of lipoproteins, glucose, homocyst(e)ine, C-reactive peptide). The relative simplicity of data collection (patient interview and exam, ABI and venipuncture) will enhance the feasibility of performing a large cross-sectional genomic study. The inclusion of both clinical and genetic data as risk predictors will allow us to identify the unique contribution of the new genetic polymorphisms.

This work will occur in the context of ongoing human genomic studies at Stanford. Transcriptional profiling for selection of candidate genes are ongoing in the laboratories of Drs. John Cooke and Thomas Quertermous which are located in the Cardiovascular Research Center (CVRC) at Stanford. The CVRC is also the administrative home for the Reynolds Center , directed by Dr. Quertermous. The programmatic effort of the Reynolds Center is to identify human genes which are preferentially expressed in the vasculature, and which are modulated in vascular disease; and to define novel polymorphisms that play a role in vascular disorders. The Reynolds Center links a unique group of talented individuals with strengths in epidemiology, biostatistics, human genetics, mouse models of human disease and DNA microarray analysis. In addition to Dr. Quertermous, these include Richard Myers who leads the Stanford effort in the Human Genome Project; Neil Risch, Professor of Genetics and a thought leader in genetic epidemiology and complex genetic disorders and Richard Olshen , Chairman of Biostatistics whose group has pioneered algorithms for analysis of the contribution of individual SNPs to complex polygenic disorders. The current proposal will leverage the strengths of the Center. Moreover, this proposal will logically lead to future collaborations with Reynolds Center faculty to determine the functionality of the polymorphisms identified by this work. The proposal builds on a foundation of translational vascular research at Stanford with a vertically integrated program in Vascular Medicine and Biology that includes molecular, cellular, and integrative physiological studies as well as clinical trials in peripheral arterial disease.