Effect Linkage And Association Studies Related Genes In Chinese Han Population ENaC Long-term Changes In Blood Pressure And A Cold Pressor Test Blood Pressure Response

Part One:Associations of epithelial sodium channel genes with longitudinal blood pressure changes in Han ChineseBackground and objectiveHigh blood pressure (BP) is the leading risk factor for cardiovascular disease and mortality worldwide. The renal epithelial sodium channel (ENaC) mediates renal reabsorption of sodium, playing a pivotal role in the control of sodium balance and BP. ENaC genes are important candidates for genetic study of the complex hypertension phenotype. We examined the associations of single nucleotide polymorphisms (SNPs) in ENaC genes with BP changes and hypertension incidence in a longitudinal family study.Subjects and methodsAll of the study participants were from the Genetic Epidemiology Network of Salt Sensitivity (GenSalt). The GenSalt study was conducted in rural areas in northen China from2003to2005. A community-based BP screening was conducted among persons aged18-60years in the study villages to identify potential probands and their families. Overall,3142Han Chinese participants from658families were enrolled in the GenSalt baseline study. Then we completed two follow-up visits during the GenSalt follow-up study, using the same standardized protocol as that of the baseline examination. All BP readings at baseline and each follow-up visit were measured using a random-zero sphygmomanometer. Of3142subjects participating in the baseline screening,341subjects were lost to follow-up and an additional46were missing genotype data. The remaining2,755Han Chinese participants were eligible for the current study. We selected43tag-SNPs in ENaC genes, including SCNN1A, SCNN1G and SCNN1B, and examined associations between the43tag-SNPs and longitudinal BP changes using a mixed linear model. After excluding625participants already diagnosed with hypertension at baseline, we further assessed the associations of43tag-SNPs with incident hypertension among2130participants, using a generalized linear mixed model. In addition, gene-based analyses were conducted using the truncated product method to evaluate the overall associations of ENaC genes with BP changes and hypertension incidence. The Bonferroni method was used to adjust for multiple testing in all analyses. ResultsDuring an average of7.4years follow-up, systolic BP (SBP) and diastolic BP (DBP) increased, and approximate33%of participants developed hypertension. SCNN1A SNP rs11064153and SCNN1G SNP rs4401050were significantly associated with longitudinal changes in SBP after adjustment for multiple testing (P=5.8×10-4and0.001, respectively). Similar but non-significant trends were observed for the associations between both rs11064153and rs4401050and DBP changes (P=0.024and0.005, respectively) and between rs11604153and hypertension incidence (P=0.017). Gene-based analyses also supported the overall association of SCNN1G with longitudinal changes in SBP (P=2.0×10-4).ConclusionWe provide the first evidence that common variants in SCNN1A and SCNN1G genes were significantly associated with longitudinal changes in BP among Han Chinese. In concordance with single-marker findings, gene-based analysis revealed potential effects of SCNN1A and SCNN1G on SBP changes. Our findings highlight that common variants in ENaC genes may play a critical role in long-term BP progression. Further studies are required to replicate these associations and to identify the causal, functional variants in ENaC genes. Part Two:Linkage and association study of blood pressure response to the cold pressor test in Han ChineseBackground and objectiveSudden cold stress is known to activate the sympathetic nervous system, resulting in vasoconstriction and subsequent increases in BP. Cardiovascular reactivity to cold stress is associated with the risk of cardiovascular disease. BP response to cold pressor test (CPT) has been documented to evaluate cardiovascular reactivity to external cold stress. However, genetic mechanisms underlying BP response to CPT remain unclear. We performed a genome-wide linkage scan and regional association analysis to identify genetic determinants of BP response to CPT. Subjects and methodsA total of1961Han Chinese participants from the GenSalt study completed the CPT. BP measurements were obtained before and after the participants immersed their left hands in ice-water for1minute. BP response to the CPT was defined as BP at time zero after ice-water immersion minus the pre-test BP. Microsatellite markers were genotyped and used for the genome-wide linkage analysis. Multipoint identity by decent (IBD) estimates were calculated using Merlin software. Multipoint quantitative trait linkage analysis was performed using SOLAR software. Then we genotyped SNPs in promising linkage regions (LOD≥2). The additive associations between single SNPs in linkage regions (LOD≥2) and BP responses to CPT were assessed using a mixed linear regression model to account for familial correlations. In addition, gene-based associations were also examined using the truncated product method. Age, gender, BMI and field center were adjusted in all analyses.ResultsSuggestive linkage signals were identified for BP responses to CPT at20p13-20p12.3, with maximum multipoint LOD scores of2.37for SBP response. Marker rs2326373, located in the5’flanking region of the SMOX gene at20p13, was significantly associated with DBP and MAP responses to CPT (P=4.6×10-5and8.8×10-6, respectively). DBP responses for genotypes GG, GA, and AA were6.83(95%CI:6.44,7.23),4.11(95%CI:2.83,5.40) and4.22(95%CI:3.13,5.32) mmHg, respectively, and MAP responses were8.97(95%CI:8.56,9.38),6.48(95%CI:5.27,7.69) and3.92(95%CI:2.80,5.03) mmHg, respectively. A similar trend was also observed for SBP response. In addition, results of gene-based analyses showed that variants in genes MCM8and SLC23A2were associated with SBP response to CPT (P=4.0×10-5and2.7×10-4, respectively), and variants in genes MCM8and STK35were associated with MAP response to CPT (P=1.5×10-5and5.0×10-5, respectively).ConclusionUnder a suggestive linkage region at20pl3-20pl2.3, we identified a novel marker near SMOX which showed strong and consistent associations with SBP, DBP and MAP responses to CPT. In addition, we identified gene-based associations of MCM8, SLC23A2and STK35in this region. Further work is warranted to confirm these findings among other populations.