PARC Abstract, 2003

Pharmacogenetics Network for Cardiovascular Risk Therapy

Goals

The overall objective of PARC is to identify natural sequence variations in candidate genes that contribute to inter-individual differences in response to drugs used to reduce risk for cardiovascular disease. The drugs selected for the current study are a statin (simvastatin) and an angiotensin converting enzyme (ACE) inhibitor (ramipril). Candidate genes are those with products in metabolic pathways that are potential targets of these drugs. DNA sequence variations in 50 genes are being determined in 23 European-Americans and 24 African-Americans, two ethnic groups with differing degrees of sequence diversity. Based on patterns of single nucleotide polymorphisms (SNPs), haplotypes are being constructed for each gene in both ethnic groups, and groups of SNP genotypes are being identified that are best able to discriminate the 3-5 most common haplotypes in each gene, present in at least 10% of the population. Haplotypes for genes related to simvastatin pharmacodynamics and pharmacokinetics (27 genes) are being determined in 1000 individuals (500 from each ethnic group) who are receiving 40 mg/day of this drug for 8 weeks, and haplotypes related to ramipril effects are being determined in a pilot study of 200 individuals (100 from each ethnic group) who are receiving 10 mg/day for 8 weeks.

Associations of these haplotypes will be sought with primary treatment endpoints for each drug: LDL cholesterol for the statin and 24 hour continuous ambulatory blood pressure for the ACE inhibitor. However, a major premise of PARC is that information regarding the contribution of candidate genes to variation in drug response can be obtained by analysis of associations of SNP haplotypes with detailed phenotypic measurement. In the case of the statin, these measurements include concentrations of individual lipoprotein sub-fractions across the entire particle spectrum as well as major apolipoproteins. For the ACE inhibitor, measurements include components of the renin-angiotensin and adrenergic systems. In addition, since both drugs are known to have anti-inflammatory effects, associations of levels of C-reactive protein, an inflammatory marker, will be sought with SNP haplotypes of the CRP gene as well as a series of other inflammatory genes that are being evaluated in Dr. Nickerson's laboratory under the auspices of another NHLBI grant.

In order to increase power to detect significant associations, and also to confirm initial findings in other populations, a series of collaborative studies is being planned. One such study that is supported by PARC as well as external funds is a trial of ACE inhibitor treatment in a group of 1531 subjects in China from whom DNA and blood pressure and other phenotypic measurements have been obtained. In addition, the high incidence of ACE inhibitor-induced cough among Chinese subjects (15% in this cohort) will allow us to test for associations of candidate genes (e.g., bradykinin receptor B2) with this side effect.

Progress

We have generated >280 kb of sequence in a total of 24 genes from 47 individuals, and discovered 1,289 SNP sites. Many of these sites have not been previously identified. We estimate that roughly 75% of the sites are not found in dbSNP, and are potentially important sites for association studies, particularly since they are not limited to coding regions.

Approximately half of the subjects for both the statin and ACE inhibitor trials have been recruited, and no significant problems have been encountered. Phenotypic data for the statin trial are being assembled, and an interim analysis of haplotype associations will be carried out on the first 250 European-Americans within the next 3 months.