Identification of Hypertension-Susceptibility Genes and Pathways by a Systemic Multiple Candidate Gene Approach: The Millennium Genome Project for Hypertension

203 Hypertens Res Vol.31 (2008) No.2 p.203-212 Original Article Identification of Hypertension-Susceptibility Genes and Pathways by a Systemic Multiple Candidate Gene Approach: The Millennium Genome Project for Hypertension Katsuhiko KOHARA1), Yasuharu TABARA2), Jun NAKURA1), Yutaka IMAI3), Takayoshi OHKUBO3), Akira HATA4), Masayoshi SOMA5), Tomohiro NAKAYAMA5), Satoshi UMEMURA6), Nobuhito HIRAWA6), Hirotsugu UESHIMA7), Yoshikuni KITA7), Toshio OGIHARA8), Tomohiro KATSUYA8), Norio TAKAHASHI9), Katsushi TOKUNAGA10), and Tetsuro MIKI1) A multiple candidate-gene approach was used to investigate not only candidate genes, but also candidate pathways involved in the regulation of blood pressure. We evaluated 307 single nucleotide polymorphisms (SNPs) in 307 genes and performed an association study between 758 cases and 726 controls. Genes were selected from among those encoding components of signal transduction pathways, including receptors, soluble carrier proteins, binding proteins, channels, enzymes, and G-proteins, that are potentially related to blood pressure regulation. In total, 38 SNPs were positively (p < 0.05) associated with hypertension. Replication of the findings and possible polygenic interaction was evaluated in five G-protein–related positive genes (GNI2, GNA14, RGS2, RGS19, RGS20) in a large cohort population (total n = 9,700, 3,305 hypertensives and 3,827 normotensive controls). In RGS20 and GNA14, dominant models for the minor allele were significantly associated with hypertension. Multiple dimension reduction (MDR) analysis revealed the presence of gene–gene interaction between GNA14 and RGS20. The MDR-proved combination of two genotypes showed a significant association with hypertension (χ2 = 9.93, p = 0.0016) with an odds ratio of the high-risk genotype of 1.168 (95% confidence interval [CI] [1.061–1.287]). After correction for all possible confounding parameters, the MDR-proved high-risk genotype was still a risk for hypertension (p = 0.0052). Furthermore, the highrisk genotype was associated with a significantly higher systolic blood pressure (133.08 ± 19.46 vs. 132.25± 19.19 mmHg, p = 0.04) and diastolic blood pressure (79.65 ± 11.49 vs. 79.01 ± 11.32 mmHg, p = 0.019) in the total population. In conclusion, a systemic multiple candidate gene approach can be used to identify From the 1)Department of Geriatric Medicine, Ehime University Graduate School of Medicine, Toon, Japan; 2)Department of Basic Medical Research and Education, Ehime University School of Medicine, Toon, Japan; 3)Department of Clinical Pharmacology and Therapeutics, Tohoku University Graduate School of Pharmaceutical Sciences and Medicine, Sendai, Japan; 4)Department of Public Health, Chiba University Graduate School of Medicine, Chiba, Japan; 5)Second Department of Internal Medicine, Nihon University School of Medicine, Tokyo, Japan; 6)Department of Medical Science and Cardiorenal Medicine, Yokohama City University Graduate School of Medicine, Yokohama, Japan; 7)Department of Health Science, Shiga University of Medical Science, Otsu, Japan; 8)Department of Geriatric Medicine, Osaka University Graduate School of Medicine, Suita, Japan; 9)Radiation Effects Research Foundation, Hiroshima, Japan; and 10)Department of Human Genetics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. This study was supported by a Grant-in-Aid for Scientific Research (12204008, 16790336) from the Ministry of Education, Culture, Sports, Science and Technology, a Grant-in-Aid for Scientific Research (H15-longevity-005) from the Ministry of Health, Labour and Welfare, and a Grant-in-Aid for Scientific Research from the Japan Arteriosclerosis Prevention Fund. Address for Reprints: Katsuhiko Kohara, M.D., Ph.D., Department of Geriatric Medicine, Ehime University Graduate School of Medicine, Shitsukawa, Toon 791–0295, Japan. E-mail: Received May 2, 2007; Accepted in revised form August 24, 2007. 204 Hypertens Res Vol. 31, No. 2 (2008) not only hypertension-susceptibility genes but also hypertension-susceptibility pathways in which related genes may synergistically collaborate through gene–gene interactions to predispose to hypertension. (Hypertens Res 2008; 31: 203–212) Key Words: hypertension, candidate gene, association study, gene–gene interaction, pathways Introduction Hypertension is one of the most common complex genetic disorders affecting a large population, with a genetic heritability ranging from 15% to 35% (1–5). Like other multifactorial human traits, hypertension is caused by the interaction of multiple risk genes and environmental risk factors (1–5). Vigorous efforts have been made to identify genes for hypertension. The candidate gene approach is a cornerstone for identifying the hypertension-susceptibility gene(s). Several candidate genes have been selected on the basis of known biochemical or physiologic components related to blood pressure regulation. However, the results of these studies have not been consistent, and the positive findings have rarely been replicated. Several underlying causes have been postulated to explain the failure of these studies to reproduce the data on candidate gene(s), including the heterogeneity of cases and controls, population stratification, and gene–gene and gene– environment interactions (1–5). In addition, it has been demonstrated that genetic interactions at multiple loci rather than a variant of a single gene underlie the genetic basis of hypertension (1–5). Hypertension is polygenic (6–8), with alleles at many different loci being suggested to contribute to the ultimate disease trait, and specific combinations of causative alleles may differ between individuals (6–9). Although several candidate genes have been associated with the development of hypertension, the mechanisms and genetic network underlying this disease remain unknown (3). It has been persuasively argued that the gene being assessed increases susceptibility for the disease, but its effect is not sufficient to cause the disease (3). Accordingly, the strategy for the candidate gene approach needs to be changed to detect polygenetic factors with weak effects. There has been a trend towards the simultaneous evaluation of several polymorphisms in separate genes (4, 10, 11). Combinations of polymorphisms at several of these loci could steadily increase the odds ratio for predicting hypertension or a hypertensive intermediate phenotype (12–16). However, the above-referenced studies were directed at genes for which there was a published association with hypertension. To search for multiple novel genes interacting with each other, it would be rational to find a specific pathway in which the genes are involved. Dominiczak et al. (17) referred to “pathwayomics,” meaning a cardiovascular continuum leading from the investigation of interrogation of multiple single nucleotide polymorphisms (SNPs) in genes for a specific pathway. No study has ever evaluated susceptibility pathway (...truncated)