Evidence for linkage and association of the markers near the LPL gene with hypertension in Chinese families

An individualized Bayesian method for estimating genomic variants of hypertension

BACKGROUND

Genomic variants of the disease are often discovered nowadays through population-based genome-wide association studies (GWAS). Identifying genomic variations potentially underlying a phenotype, such as hypertension, in an individual is important for designing personalized treatment; however, population-level models, such as GWAS, may not capture all the important, individualized factors well. In addition, GWAS typically requires a large sample size to detect the association of low-frequency genomic variants with sufficient power. Here, we report an individualized Bayesian inference (IBI) algorithm for estimating the genomic variants that influence complex traits, such as hypertension, at the level of an individual (e.g., a patient). By modeling at the level of the individual, IBI seeks to find genomic variants observed in the individual's genome that provide a strong explanation of the phenotype observed in this individual.

RESULTS

We applied the IBI algorithm to the data from the Framingham Heart Study to explore the genomic influences of hypertension. Among the top-ranking variants identified by IBI and GWAS, there is a significant number of shared variants (intersection); the unique variants identified only by IBI tend to have relatively lower minor allele frequency than those identified by GWAS. In addition, IBI discovered more individualized and diverse variants that explain hypertension patients better than GWAS. Furthermore, IBI found several well-known low-frequency variants as well as genes related to blood pressure that GWAS missed in the same cohort. Finally, IBI identified top-ranked variants that predicted hypertension better than GWAS, according to the area under the ROC curve.

CONCLUSIONS

The results support IBI as a promising approach for complementing GWAS, especially in detecting low-frequency genomic variants as well as learning personalized genomic variants of clinical traits and disease, such as the complex trait of hypertension, to help advance precision medicine.

Association of 3 single nucleotide polymorphisms of the eighth chromosome with remodeling of the myocardium and carotid arteries in the Kazakh population

ABSTRACT

Cardiovascular diseases are one of the key health issues in Kazakhstan. According to the WHO, the prevalence of arterial hypertension (AH) was 28% in males and 25% in females in 2015, which puts up vastly to premature mortality from non-communicable diseases.The search for genetic features of target organ lesions processes in AH is relevant. The goal of this study was to search for the genetic markers of myocardial remodeling (MR) and carotid artery remodeling (CAR).A total of 866 hypertensive individuals were recruited in Nur-Sultan, Kazakhstan. Their blood was genotyped for 9 single nucleotide polymorphisms (SNPs) of the eighth chromosome to find an association with remodeling. The analysis was carried out in the group pairs (control and CAR, control and MR, and control and CAR and MR). The genotype-phenotype association was assessed using 5 different inheritance models: dominant, codominant, recessive, overdominant, and log-additive.Statistically significant results were found for 3 SNPs (rs2407103, rs11775334, rs2071518) which minor alleles enlarged risks of MR and CAR in AH in the studied population. Three polymorphisms have previously been associated with АН and some other traits like pulse pressure and blood glucose in other ethnic populations: rs2407103 - in Afro-American population, rs11775334 - in the European population, rs2071518 is well studied in various ethnic populations (European, South Asian, Afro-American, Hispanic, East Asian).

Meta-based association of the lipoprotein lipase gene S447X variant with hypertension and blood pressure variation

Association of the lipoprotein lipase (LPL) gene S447X variant with hypertension has been investigated extensively, whereas the results are often irreproducible. We therefore conducted a meta-analysis to examine whether S447X variant was associated with hypertension and blood pressure variation. Case-control reports published in English language and humans were identified from MEDLINE, EMBASE and Web of Science search engines as of 10 December 2009. Fixed-effects model was applied to pool data in the absence of between-studies heterogeneity, and random-effects model otherwise. A total of five studies (960 cases and 1145 controls) for hypertension and four studies (n=2777) for blood pressure were included. Compared with 447SS homogeneous carriers, those with 447X variant had a lower risk of hypertension (odds ratio (OR)=0.78; 95% confidence interval (CI): 0.62-0.98; P=0.03), and this effect reached significance under the fixed-effects model (I(2)=30% and P=0.22). Similarly, compared with 447S allele carriers, those with 447X allele carriers also had a lower risk of hypertension (OR=0.79; 95% CI: 0.64-0.98; P=0.03). In case of pregnancy-induced hypertension, no significance was observed (P>0.05). As for blood pressure association, there was no significant difference between 447X variant and 447SS homogeneous carriers for both systolic and diastolic blood pressure in the whole population, even stratified by gender (P>0.05). The Egger test told no publication bias for all associations. This meta-analysis demonstrated that LPL gene S447X variant was significantly associated with hypertension and showed no obvious relation with pregnancy-induced hypertension and blood pressure variation.

The common biological basis for common complex diseases: evidence from lipoprotein lipase gene

The lipoprotein lipase (LPL) gene encodes a rate-limiting enzyme protein that has a key role in the hydrolysis of triglycerides. Hypertriglyceridemia, one widely prevalent syndrome of LPL deficiency and dysfunction, may be a risk factor in the development of dyslipidemia, type II diabetes (T2D), essential hypertension (EH), coronary heart disease (CHD) and Alzheimer's disease (AD). Findings from earlier studies indicate that LPL may have a role in the pathology of these diseases and therefore is a common or shared biological basis for these common complex diseases. To examine this hypothesis, we reviewed articles on the molecular structure, expression and function of the LPL gene, and its potential role in the etiology of diseases. Evidence from these studies indicate that LPL dysfunction is involved in dyslipidemia, T2D, EH, CHD and AD; and support the hypothesis that there is a common or shared biological basis for these common complex diseases.

Lipoprotein lipase variants associated with an endophenotype of hypertension: hypertension combined with elevated triglycerides

Previously, we observed that young-onset hypertension was independently associated with elevated plasma triglyceride(s) (TG) levels to a greater extent than other metabolic risk factors. Thus, focusing on the endophenotype--hypertension combined with elevated TG--we designed a family-based haplotype association study to explore its genetic connection with novel genetic variants of lipoprotein lipase gene (LPL), which encodes a major lipid metabolizing enzyme. Young-onset hypertension probands and their families were recruited, numbering 1,002 individuals from 345 families. Single-nucleotide polymorphism discovery for LPL, linkage disequilibrium (LD) analysis, transmission disequilibrium tests (TDT), bin construction, haplotype TDT association and logistic regression analysis were performed. We found that the CC- haplotype (i) spanning from intron 2 to intron 4 and the ACATT haplotype (ii) spanning from intron 5 to intron 6 were significantly associated with hypertension-related phenotypes: hypertension (ii, P=0.05), elevated TG (i, P=0.01), and hypertension combined with elevated TG (i, P=0.001; ii, P<0.0001), according to TDT. The risk of this hypertension subtype increased with the number of risk haplotypes in the two loci, using logistic regression model after adjusting within-family correlation. The relationships between LPL variants and hypertension-related disorders were also confirmed by an independent association study. Finally, we showed a trend that individuals with homozygous risk haplotypes had decreased LPL expression after a fatty meal, as opposed to those with protective haplotypes. In conclusion, this study strongly suggests that two LPL intronic variants may be associated with development of the hypertension endophenotype with elevated TG.

Analysis of phenotype-genotype connection: the story of dissecting disease pathogenesis in genomic era in China, and beyond

DNA is the ultimate depository of biological complexity. Thus, in order to understand life and gain insights into disease pathogenesis, genetic information embedded in the sequence of DNA base pairs comprising chromosomes should be deciphered. The stories of investigating the association between phenotype and genotype in China and other countries further demonstrate that genomics can serve as a probe for disease biology. We now know that in Mendelian disorders, one gene is not only a dictator of one phenotype but also a dictator of two or more distinct disorders. Dissecting genetic abnormalities of complex diseases, including diabetes, hypertension, mental diseases, coronary heart disease and cancer, may unravel the complicated networks and crosstalks, and help to simplify the complexity of the disease. The transcriptome and proteomic analysis for medicine not only deepen our understanding of disease pathogenesis, but also provide novel diagnostic and therapeutic strategies. Taken together, genomic research offers a new opportunity for determining how diseases occur, by taking advantage of experiments of nature and a growing array of sophisticated research tools to identify the molecular abnormalities underlying disease processes. We should be ready for the advent of genomic medicine, and put the genome into the doctors' bag, so that we can help patients to conquer diseases.

Association of alpha1A adrenergic receptor gene variants on chromosome 8p21 with human stage 2 hypertension

OBJECTIVE AND DESIGN

We previously reported a significant linkage between human chromosome 8p22 with essential hypertension and systolic blood pressure levels. On the basis of this, we used an efficient age, sex and area-matched case-control scheme to test the association of the polymorphisms in the human alpha1A adrenergic receptor (ADRA1A) gene, located on chromosome 8p21-p11.2, with essential hypertension in a northern Han Chinese population.

METHODS

Seven polymorphisms were identified by direct sequencing of genomic DNA derived from 48 randomly recruited hypertensive and 48 healthy subjects. They were also examined for association with essential hypertension in 480 stage 2 hypertensive individuals and their individually matched controls.

RESULTS

We observed significantly higher frequencies of the 347Arg allele and 2547G alleles in the cases compared with their controls (P = 0.04 and 0.007, respectively). McNemar's test revealed that carriers of 2547G alleles were at a greater risk of essential hypertension with an odds ratio of 3.00 [95% confidence interval (CI) 1.23-8.35]. We then performed a conditional logistic regression to adjust the effects of conventional risk factors, revealing an odds ratio of 2.84 for carriers of the 2547G allele (95% CI 1.15-6.99). With the haplotypic probabilities estimated using PHASE software, we performed haplotype trend regression analysis, showing a significant association between haplotype 7 and essential hypertension (P = 0.02), after adjustment for conventional risk factors.

CONCLUSIONS

Our findings suggest that the genetic variations in the ADRA1A gene are significantly associated with essential hypertension, and may play an important role in the development of essential hypertension in this Chinese population.

Association Study With 33 Single-Nucleotide Polymorphisms in 11 Candidate Genes for Hypertension in Chinese

Essential hypertension is considered to be a typical complex disease with multifactorial etiology, which leads to inconsistent findings in genetic studies. One possibility of failure to replicate some single-locus results is that the underlying genetics of hypertension are not only based on multiple genes with minor effects but also on gene-gene interactions. To test this hypothesis, a case-control study was constructed in Chinese subjects, detecting both single locus and multilocus effects. Eleven candidate genes were selected from biochemical pathways that have been implicated in the development and progression of hypertension, and 33 polymorphisms were evaluated in 503 hypertension patients and 490 age- and gender-matched controls. Single-locus associations, using traditional logistic regression analyses, and multilocus associations, using classification and regression trees and multivariate adaptive regression splines, were both explored in this study. Final models were selected using either Bonferroni correction or cross-validation. Three polymorphisms, TH*rs2070762, ADRB2*Q27E, and GRK4*A486V, were found to be independently associated with essential hypertension in Chinese subjects. In addition to these individual predictors, a potential interaction of CYP11B2-AGTR1 is also involved in the etiology of hypertension. These findings support the multigenic nature of the etiology of essential hypertension and propose a potential gene-gene interactive model for future studies.

Lipoprotein Lipase Gene is Linked and Associated with Hypertension in Taiwan Young-onset Hypertension Genetic Study

Hypertriglyceridemia has been extensively associated with hypertension. However, the mechanism behind it is poorly understood. A positive linkage signal between Lipoprotein lipase (LPL) and young-onset hypertension has been identified by us as the strongest among 18 candidate genes. Here we report our fine mapping works with seven microsatellite markers flanking LPL, sequencing results for its promoter and exons, and an extended association study with the identified single nucleotide polymorphisms(SNP). First, using data from 213 individuals in 59 nuclear families of young-onset hypertension, multipoint analysis revealed a NPL score of 3.02 for the LPL (GZ-14/GZ-15) marker in intron 6. LPL marker (p < 10(-12)) and the haplotypes containing its allele 1 (p < 0.0001) were also significantly associated with young hypertension by transmission disequilibrium test. In-depth sequencing revealed no mutation in promoter and exon regions, except two cSNP: 7754C--> A (C/A: 0.91/0.09), a silent mutation in exon 8 and S447X (C/G: 0.92/0.08), a stop codon mutation in exon 9. Other 11 cSNPs documented in NCBI GenBank are absent in our sample. Constructed from the above 2 cSNPs, haplotype AC showed a moderate TDT association with elevated triglyceride (p = 0.02) and with hypertension and elevated triglyceride combined (p = 0.06). Again, in an extended case-control study, a significant association was found between S447X and patients with persistent hypertension and elevated triglyceride (p = 0.02). We conclude that LPL variants may play a causal role in the development of hypertension in Taiwan Han Chinese. The moderate association with SNP haplotype suggests that other regulatory LPL variant may exist.

Linkage analysis of chromosome 1 with essential hypertension and blood pressure quantitative traits in Chinese families

Summary Several recent studies have linked human chromosome 1p to essential hypertension (EH) or blood pressure (BP) levels. In an independent population of 148 hypertensive families from China we tested these findings. Thirty highly informative microsatellite markers spanning about 284 cM were genotyped. Qualitative linkage analysis was conducted using non-parametric linkage analysis implemented within the GENEHUNTER 2.0 software, whereas quantitative analysis was performed with the variance-component method integrated in the S.O.L.A.R. 1.7.4. software with an additional Haseman-Elston method using the SAGE/SIBPAL2 program. We observed suggestive linkage between D1S2890 (1p31, 80.9 cM) and hypertension using the multipoint non-parametric linkage analysis (NPL = 2.19, P = 0.01). In the quantitative analysis we didn't observe a significant excess of identity-by-descent allele sharing between the systolic blood pressure levels and the markers. However, the D1S207 microsatellite marker (1p21) which is located about 107 cM from the telomere of 1p showed weak linkage evidence with the diastolic blood pressure levels (LOD = 1.42). These findings suggest linkage of 1p31 with essential hypertension in the ethnic Chinese, and provide a potential clue for future studies involving candidate genes for hypertension.

Linkage and linkage disequilibrium analysis of the lipoprotein lipase gene with lipid profiles in Chinese hypertensive families

Elevated TG [triacylglycerol (triglyceride)] is a significant independent risk factor for cardiovascular disease. LPL (lipoprotein lipase) is one of the key enzymes in the metabolism of the TG-rich lipoproteins which hydrolyses TG from the chylomicrons and very-LDL (low-density lipoprotein). To investigate the relationship between the LPL gene and lipid profiles, especially TG, in 148 hypertensive families, we have chosen seven flanking microsatellite markers and four internal markers of the LPL gene and conducted linkage analysis by SOLAR and S.A.G.E. (statistical analysis for genetic epidemiology)/SIBPAL 2 programs, and linkage disequilibrium analysis by QTDT (quantitative transmission/disequilibrium test) and GOLD (graphical overview of linkage disequilibrium). There were statistically significant differences in lipid levels between subjects without and with hypertension within families. A maximum LOD score of 1.3 with TG at the marker D8S261 was observed by SOLAR. Using S.A.G.E./SIBPAL 2, we identified a linkage with TG at the marker 'ATTT' located within intron 6 of the LPL gene (P=0.0095). Two SNPs (single nucleotide polymorphisms), HindIII and HinfI, were found in linkage disequilibrium with LDL-cholesterol levels (P=0.0178 and P=0.0088 respectively). A strong linkage disequilibrium was observed between the HindIII in intron 8 and HinfI in the exon 9 (P<0.00001, D'=0.895). Linkage disequilibrium was also found between the 'ATTT' polymorphism in intron 6 and two SNPs (P=0.0021 and D'=0.611 for HindIII; and P=0.00004, D'=0.459 for HinfI). The present study in the Chinese families with hypertension suggested that the LPL gene might influence lipid levels, especially TG metabolism. Replication studies both in Chinese and other populations are warranted to confirm these results.

The S447X polymorphism of the lipoprotein lipase gene is associated with lipoprotein lipid and blood pressure levels in Chinese patients with essential hypertension

OBJECTIVE

To investigate the association between the S447X polymorphism of the lipoprotein lipase (LPL) gene and lipoprotein lipid and blood pressure (BP) levels in 904 Chinese subjects with essential hypertension.

METHOD

Five hundred and sixty-three male and 341 female patients (aged 35-69 years) were randomly selected from hypertensive patients diagnosed in the Community-based Comprehensive Studies on Prevention and Control of Hypertension Project in China (CCPACH) and not treated with antihypertensive medications for at least 2 weeks immediately before blood collection.

RESULTS

After multivariate adjustment for age, body mass index (BMI), smoking status, alcohol intake and serum glucose, the X447 allele was significantly associated with low triglyceride, log triglyceride : high-density lipoprotein (HDL)-cholesterol ratio and high HDL-cholesterol levels compared with the S447S genotype, but not with BP levels in the whole study population. However, upon stratification for dyslipidemic status, the X447 allele was associated with higher systolic blood pressure (SBP) (P < 0.05) and pulse pressure (PP) (P < 0.05) compared with the S447S genotype after multivariate adjustment in dyslipidemic subjects, but not in those without dyslipidemia. A statistically significant interaction between the LPL S447X polymorphism and dyslipidemic status was observed for SBP and PP levels, suggesting that dyslipidemic status might modify the effect of the LPL S447X polymorphism on BP levels.

CONCLUSIONS

Our findings suggest that a high concentration of triglyceride and/or low concentration of HDL-cholesterol are associated with high SBP and PP in hypertensive patients with the X447 allele of the LPL gene.

Human genome research in China

Significant progress in human genome research has been made in China since 1994. This review aims to give a brief and incomplete introduction to the major research institutions and their achievements in human genome sequencing and functional genomics in medicine, with emphasis on the "1% Sequencing Project", the generation of single nucleotide polymorphism and haplotype maps of the human genome, disease gene identification, and the molecular characterization of leukemia and other diseases. Chinese efforts towards the sequencing of pathogenic microbial genomes and of the rice (Oryza sativa ssp. Indica) genome are also described.

Lipoprotein Lipase Gene Polymorphisms and Blood Pressure Levels in the Northern Chinese Han Population

The lipoprotein lipase (LPL) gene has been investigated extensively in linkage studies and in studies of its association with lipid profiles and coronary artery disease (CAD), and this gene has also been reported to have an association with hypertension. In our previous linkage study on 148 Chinese hypertensive families, the regions at or near the LPL gene were found to be associated with systolic blood pressure (SBP) and diastolic blood pressure (DBP). Thus the LPL gene is a logical candidate gene for involvement in the underlying cause of essential hypertension (EH). In the present study, we identified 22 sequence variants by directly sequencing 10 exons and flanking regions of the LPL gene, and investigated the occurrence of 3 of these variants, IVS4-214C>T, 7754C>A and S447X, in a case-control study including 501 normotensive (NT) subjects and 497 EH subjects. In males, the frequencies of the genotypes of each of the 3 variants did not differ significantly between the NT and EH groups. Among the EH group in females, ANCOVA revealed no significant difference in blood pressure levels according to the 7754C>A genotype. However, in female, the distribution of the 7754C>A genotype and the frequency of the A allele of 7754C>A differed significantly between the NT and EH groups (p=0.032 and p=0.027, respectively) with 0.78 (95% confidence interval (CI): 0.56 to 1.07; p=0.12) of odds ratio for the A allele. Moreover, haplotype analysis revealed that T-A-C and T-C-G haplotypes (in the order of IVS4-214C>T, 7754C>A and S447X) were statistically more frequent in the NT group than in the EH group in females and males, respectively. Our indivisual single nucleotide polymorphism (SNP) analysis did not provide substantial evidence of an association between polymorphisms in the LPL gene and hypertension status and/or blood pressure levels in this cohort, but the more powerful haplotypes analysis suggested an association between the LPL gene and hypertension.