Chinese Han Population Klkb1 And Tert Gene With Essential Hypertension Association Studies

SECTION ONEBackground (KLKB1)Essential hypertension is a complex disease where both genetic and environmental factors interact to produce the phenotype. The genetic contribution to blood pressure (BP) variation ranges from 30 to 50%. It is likely that a number of genes with smaller effects account for the heritability of this complex disorder.Plasma kallikrein is a serine protease that is synthesized in the liver as plasma prekallikrein, secreted into the blood, and converted into plasma kallikrein. Then lasma kallikrein acts on high molecular weight kininogen substrate to release bradykinin and converts prorenin to renin. By controlling the release of bradykinin (a potent vasodilator) and the activation of renin (the protease converting angiotensinogen to angiotensinâ… ), plasma kallikrein is deeply involved in BP regulation. Based on the physiological effects, human plasma kallikrein gene (KLKB1) encoding plasma kallikrein can be considered as a good candidate gene for essential hypertension. So far, the association of the variation in the KLKB1 gene with hypertension has not been explored.The haplotype-based association studies may be inherently more powerful than individual SNP analysis to identify causal genetic variants underlying complex disease, since the method incorporates LD information from multiple markers. The increasing knowledge of how the pattern of LD varies across human genome has enabled the design of selecting a minimum number of SNPs (tag SNPs) to capture most of the haplotypic diversity, and several approaches have been suggested for identifying these optimal tag SNPs. The international HapMap project is a resource that provides empirical genome-wide data to support such analyses.In the present study, we have employed the haplotype-based approach to examine the contribution of common variation in the KLKB1 gene to the risk of hypertension in a population-based case-control study. Methods (KLKB1)The samples involved in the present study consisted of 2586 (1317 unrelated hypertensive cases and 1269 unrelated normotensive) Han Chinese. All DNA samples and clinical data were collected from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA). The measurements and interviews were taken under standard conditions. Essential hypertension was defined as SBP≥150 mmHg and/or DBP≥95 mmHg on three blood pressure measurements, or take medications for hypertension. The control subjects had SBP＜140 mmHg and DBP＜90 mmHg. We searched the HapMap data (Phaseâ… ) and selected common SNPs, and then determined the pattern of linkage disequilibrium (LD) and haplotype structure within the KLKB1 gene. Tag SNPs were selected by program tagSNPs and htSNP₂, and were genotyped by means of polymerase chain reaction (PCR) and restriction fragment-length polymorphism (RFLP) method. Analyses were done separately for each of the tag SNPs and followed by haplotype analyses. The genotypic and allelic frequencies between cases and controls were compared by the chi square (x²) test. Logistic regression analysis was used to assess whether the genetic variation was associated independently with hypertension after adjustment for covariates. The statistical analysis was performed with STATA 8.0 for Windows. Haplo. stats software was used to test the association of statistically inferred haplotypes with essential hypertension. Genasso program was used to predict the association of other ungenotyped SNPs with essential hypertension.Results (KLKB1)There was no significant difference in age, gender, status of drinking and smoking between cases and controls. Eight common SNPs were identified in CHB in HapMap project, the same set of four tag SNPs, rs2278542, rs2304595, rs4253325, and rs925453 were selected by tagSNPs and htSNP₂ programs. Single SNP analyses indicated that SNPs rs2304595 and rs4253325 were significantly associated with hypertension after adjustment for covariates. Compared with the most common Hap2 CAGC, Hap1 AGAC and Hap3 CGAC which carry the susceptible rs2304595 G allele and rs4253325 A allele were found to significantly increase the risk of essential hypertension with adjusted odds ratios equal to 1.35 .and 1.17, respectively (P＜0.0001 and 0.028). A strongly significant interaction with gene-drinking was also observed. Among drinkers, the adjusted OR for Hapl relative to Hap2 was increased to 2.50 (95% CI, 2.40 to 2.61, P＜0.0001).Conclusion (KLKB1)This was the first study to perform association analysis of the KLKB1 gene with essential hypertension. Our findings suggested that common genetic variation in the KLKB1 gene might contribute to the risk of hypertension in the northern Han Chinese population. SECTION TWOBackground (TERT)Telomeres—the specialized DNA-protein structures at the ends of eukaryotic chromosomes—are essential for maintaining genome stability and integrity and for extended proliferative life span in both cultured cells and in the whole organism. Telomerase and additional telomere-associated proteins are necessary for preserving telomeric DNA length. Telomere dysfunction is emerging as an important factor in the pathogenesis of hypertension, atherosclerosis, and heart failure. Several studies have examined the potential relationship between telomere length and human hypertension. Telomerase has been implicated as an important regulator of VSMC proliferation. Given these findings, we hypothesized that telomerase deficiency and telomere shortening may modify the phenotypic characteristics of vascular cells in a way that favors development of hypertension. Telomerase comprises two principal subunits: telomerase reverse transcriptase (TERT) and the telomerase RNA component (TERC). Transcriptional regulation of TERT has a key role in telomerase activity and telomere shortening. Therefore, we focused on the TERT promoter region in this study. We performed a case-control study to assess the effect of common genetic variation in the TERT promoter region on the risk of essential hypertension.Methods (TERT)The samples involved in the present study consisted of 2586 (1317 unrelated hypertensive cases and 1269 unrelated normotensive) Hart Chinese. All DNA samples and clinical data were collected from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA). The measurements and interviews were taken under standard conditions. Essential hypertension was defined as SBP≥150 mmHg and/or DBP≥95 mmHg on three blood pressure measurements, or take medications for hypertension. All the control subjects had SBP＜140 mmHg and DBP＜90 mmHg. Two polymorphisms in TERT promoter region, rs2736109 and rs2735940, were selected and were genotyped by PCR-RFLP method. The genotypic and allelic frequencies between cases and controls were compared by the chi square (χ²) test. Logistic regression analysis was used to assess whether the genetic variation was associated independently with hypertension after adjustment for covariates. The statistical analysis was performed with STATA 8.0 for Windows. Haplo.stats software implemented in R environment was used to test the association of haplotypes with essential hypertension. All statistical tests were two-tailed, and P＜0.05 was considered statistically significant.Results (TERT)No significant deviation from Hardy-Weinberg equilibrium was found for two polymorphisms. There were no significantly differences in the genotypic and allelic frequencies between cases and controls. Logitstic regression analyses revealed that the lack of association still persisted after adjustment for other environmental factors. The haplotype analysis showed that Hap1 (AC) significantly decreased the risk of hypertension. Compared with the Hap3, the adjusted odds ratio was 0.79 (95% CI 0.78-0.80, P＜0.0001) for Hap1.Conclusions (TERT)This was the first study to perform association analysis of the TERT gene with essential hypertension. Our findings suggested that haplotype AC might decrease the risk of hypertension in the northern Han Chinese population. Our observations are based on small numbers and might be interpreted with caution because this initial finding has not yet been confirmed in other separate population.