Angiotensin II type 1 receptor gene polymorphism and telomere shortening in essential hypertension

Several genetic studies were carried out among hypertensive patients to assess allelic association at the 1166 position of the 3' untranslated region of angiotensin II type 1 receptor gene. In addition, attempts have also been made to find out whether telomere length attrition is associated with hypertension. The main aim of this study was to examine the association of A1166C polymorphism of angiotensin II type 1 receptor and telomere length with essential hypertension in Egyptian people. Angiotensin II type 1 genotyping and relative telomere length were investigated by PCR in 40 patients of essential hypertension and 15 healthy controls. The homozygous AA1166 allele frequency was 92.8% among the studied subjects. There was no intergroup variation in A allele frequency in normotensive group. The frequency of homozygous A allele was significantly higher in hypertensive than normotensive subjects (97.5 and 80%, respectively) with higher frequencies in male patients. The average telomere length ratio was significantly shorter in hypertensive than in normal subjects (1.08?±?0.3 and 1.54?±?0.18, respectively). No correlation was observed between telomere length ratio and body mass index. This study suggests that the homozygous A1166 allele of angiotensin II type 1 and short telomeres may be predisposing factors for essential hypertension in Egyptians and may be involved in the pathogenesis of the disease. Further strategies for treating high-risk patients could result in prevention or delay of end organ damage.     

A Genome-Wide Methylation Study on Essential Hypertension in Young African American Males

Objective

There is emerging evidence from animal studies suggesting a key role for methylation in the pathogenesis of essential hypertension. However, to date, very few studies have investigated the role of methylation in the development of human hypertension, and none has taken a genome-wide approach. Based on the recent studies that highlight the involvement of inflammation in the development of hypertension, we hypothesize that changes in DNA methylation of leukocytes are involved in the pathogenesis of hypertension.

Method & Results

We conducted a genome-wide methylation analysis on 8 hypertensive cases and 8 normotensive age-matched controls aged 14–23 years and performed validation of the most significant CpG sites in 2 genes in an independent sample of 36 hypertensive cases and 60 normotensive controls aged 14–30 years. Validation of the CpG sites in the SULF1 gene was further conducted in a second replication sample of 36 hypertensive cases and 34 controls aged 15.8–40 years. A CpG site in the SULF1 gene showed higher methylation levels in cases than in healthy controls in the genome-wide step (p = 6.2×10⁻⁵), which was confirmed in the validation step (p = 0.011) for subjects ≤30 years old but was not significant for subjects of all ages combined (p = 0.095).

Conclusion

The identification of a difference in a blood leukocyte DNA methylation site between hypertensive cases and normotensive controls suggests that changes in DNA methylation may play an important role in the pathogenesis of hypertension. The age dependency of the effect further suggests complexity of epigenetic regulation in this age-related disease.     

Phenotypic selection: a successful strategy to fix major genes of hypertension.

Hypertension is dominantly inherited in cross hybrids between hypertensive SHR/Mol and normotensive BB/OK rats. We used these cross hybrids for repeated backcrossing of selected hypertensive animals onto normotensive BB/OK rats to fix high blood pressure and to generate a hypertensive and diabetic BB/OK rat subline. After 8 backcrosses, the backcross parents were genetically analysed with the aid of 259 microsatellite markers to identify SHR genes causing blood pressure of 177 +/- 10 mmHg in this BB/OK rat subline. Loci on chromosomes 1, 14 and 18 showed longest heterozygosity. These loci might contain major genes of the SHR rat causing hypertension in this BB/OK rat subline. This classical strategy seems to be most suitable to fix major genes of hypertension in particular and complex traits in general and therefore to generate new animal models.     

Lack of association of variants of the renal salt reabsorption-related genes SLC12A3 and ClC-Kb and hypertension in Mongolian and Han populations in Inner Mongolia

Abnormalities in renal sodium chloride and water reabsorption play important roles in the development of hypertension. Mutations in the genes involved in renal sodium chloride reabsorption can affect blood pressure. Recently, the R904Q variant of the sodium/chloride transporters, member 3 (SLC12A3) gene and the T481S variant of the chloride channel Kb (ClC-Kb) gene were found to be implicated in essential hypertension. We investigated a possible role of the SLC12A3 and ClC-Kb genes in the prevalence of essential hypertension in the Mongolian and Han ethnic groups. The study population comprised 308 unrelated Mongolians with essential hypertension, 271 Mongolian normotensives, 285 unrelated Han with essential hypertension, and 194 Han normotensives living in Inner Mongolia. The presence of the SLC12A3 R904Q and ClC-Kb-T481S polymorphisms was determined using TaqMan PCR. The risk factors for hypertension were age, body mass index, alcohol consumption, total plasma cholesterol, and low-density lipoprotein cholesterol. The genotype and allele frequencies of SLC12A3 R904Q and ClC-Kb-T481S were not significantly different between hypertensive patients and controls in the Mongolian (SLC12A3 R904Q, P = 0.471 and P = 0.494, ClC-Kb-T481S, P = 0.960 and P = 0.960, respectively) and Han (SLC12A3 R904Q, P = 0.765 and P = 0.777, ClC-Kb-T481S, P = 0.100 and P = 0.103, respectively) populations. There was no significant association between the SLC12A3 R904Q variant and the ClC-Kb-T481S variant and essential hypertension in either ethnic group.     

A search for genetic loci responsible for emotional stress-induced arterial hypertension in the ISIAH rats

Hypertension is a widespread human disease caused by a complex interaction of a series of the genetic factors with both each other and the environmental conditions. In this study we aimed at determining the candidate genetic loci responsible for hypertension in the ISIAH rats and studying the dynamics of the relevant genetic and physiological mechanisms in rat ontogeny. The candidate genetic loci were identified from association of the microsatellite markers linked to these loci with arterial hypertension in rat F2 hybrids exposed to stress. Two populations of F2 hybrids of different age (3-4 and 6 months) were obtained by crossing hypertensive ISIAH and normotensive WAG rats. We present the results of cosegregation analysis for the following loci: the gene for the Na+, K(+)-ATPase alpha 1 subunit isoform (Atp1a1), the endothelin-2 gene (Edn2), the low affinity nerve growth factor receptor gene (Lngfr), and a region of chromosome 10 marked with the D10Rat58 microsatellile located 3 cM away of the aldolase C gene (AldC). The results obtained allowed us to localize the genes responsible for the stress-induced arterial hypertension in the ISIAH rats to the Atp1a1 locus (P < 0.05), chromosome 2 and to the Lngfr gene locus (P < 0.05), chromosome 10. The association of hypertensive status with the Lngfr gene was found only in young ISIAH rats whereas in adult rats of this line, hypertension was associated with the Atp1a1 locus.     

The renal urate transporter SLC17A1 locus: confirmation of association with gout

Introduction

Two major gout-causing genes have been identified, the urate transport genes SLC2A9 and ABCG2. Variation within the SLC17A1 locus, which encodes sodium-dependent phosphate transporter 1, a renal transporter of uric acid, has also been associated with serum urate concentration. However, evidence for association with gout is equivocal. We investigated the association of the SLC17A1 locus with gout in New Zealand sample sets.

Methods

Five variants (rs1165196, rs1183201, rs9358890, rs3799344, rs12664474) were genotyped across a New Zealand sample set totaling 971 cases and 1,742 controls. Cases were ascertained according to American Rheumatism Association criteria. Two population groups were studied: Caucasian and Polynesian.

Results

At rs1183201 (SLC17A1), evidence for association with gout was observed in both the Caucasian (odds ratio (OR) = 0.67, P = 3.0 × 10^-6) and Polynesian (OR = 0.74, P = 3.0 × 10^-3) groups. Meta-analysis confirmed association of rs1183201 with gout at a genome-wide level of significance (OR = 0.70, P = 3.0 × 10^-8). Haplotype analysis suggested the presence of a common protective haplotype.

Conclusion

We confirm the SLC17A1 locus as the third associated with gout at a genome-wide level of significance.     

Influence of ovariectomy on cardiac oxidative stress in a renovascular hypertension model

The aim of this study was to evaluate the potential influence of endogenous ovarian hormones on cardiac oxidative stress in renovascular hypertension. Female Wistar rats (N = 10 per group) were divided among 4 groups: (i) normotensive control; (ii) hypertensive control; (iii) normotensive ovariectomized; and (iv) hypertensive ovariectomized rats. To induce hypertension, 2-kidney 1-clip (2K1C) Goldblatt's method was followed. Blood pressure (BP) was enhanced (25%) in 2K1C and it was not further altered in hypertensive ovariectomized animals. Lipid peroxidation (measured by thiobarbituric acid reactive substances; TBARS) increased in heart homogenates after ovariectomy (253%) and was additionally augmented when associated with hypertension (by 28%). Superoxide dismutase and catalase activities were similar in both hypertensive groups. Hypertension enhanced glutathione peroxidase activity (75%), but the association with ovariectomy prevented this change. Total radical trapping antioxidant potential (TRAP) decreased in hypertensive rats (34%) and was recovered when associated with ovariectomy. However, this adaptation seems not to be sufficient to avoid the increased oxidative damage in ovariectomized hypertensive animals. These results suggest a protective role for physiological ovarian hormones in the cardiac oxidative stress induced by 2K1C hypertension.     

Endothelin-1 gene and endothelial nitric oxide synthase gene polymorphisms in adolescents with juvenile and obesity-associated hypertension

Hypertension is an increasing public health problem all over the world. Essential hypertension accounts for more than 90% of cases of hypertension. It is a complex genetic, environmental and demographic trait. New method in molecular biology has been proposed a number of candidate genes, but the linkage or association with hypertension has been problematic (lack of gene-gene and gene-environment interaction). It is well known that genetic influences are more important in younger hypertensives, because children are relatively free from the common environmental factors contributing to essential hypertension. The association studies compare genotype ferquencies of the candidate gene between patient groups and the controls, in pathways known to be involved in blood pressure regulation. This study examined three polymorphisms of these factors encoding genes (ET-1 G+5665T (Lys198Asn), endothelial nitric oxide synthase (eNOS) T-786C promoter polymorphism and 27-bp repeat polymorphism in intron 4) in adolescents with juvenile essential and obesity-associated hypertension. Significant differences were found in the G/T genotype of the ET-1 polymorphism in the hypertensive and obese+hypertensive patients (body mass index (BMI) > 30). A strong association was detected between the BMI and the polymorphism of the ET-1 gene. It seems that ET-1 gene polymorphism plays a role in the development of juvenile hypertension associated with obesity. Although no significant differences were seen in the case of the eNOS promoter polymorphism and the eNOS 4th intron 27-bp repeat polymorphism. It seems that eNOS may play a role, but this is not the main factor in the control of blood pressure; it is rather a fine regulator in this process. This study with adolescents facilitates an understanding of the genetic factors promoting juvenile hypertension and obesity.     

Replication of an African-American GWAS on blood pressure and hypertension in the Korean population

Hypertension is a complex disease that is caused by the interaction of multiple genetic and environmental risk factors, affecting 30% adult in industrialized countries. The identification of genetic factors that impact one’s predisposition to hypertension and its progression is an ongoing challenge. A genome-wide association study of African-Americans, who have one of the highest rates of hypertension in the world, was reported. We replicated the GWAS results in 8842 unrelated Koreans. Fifteen of the 30 reported SNPs were analyzed for their association with blood pressure and hypertension. Linear regression was used to analyze blood pressure as a quantitative trait in 7551 subjects, and a case-control study was performed using 1968 hypertensive cases and 4452 normotensive controls by logistic regression analysis. The quantitative trait study demonstrated a moderate association of 2 SNPs, rs9301196 (p=4.9×10^?3 for diastolic blood pressure) and rs2823756 (p=0.04 for systolic blood pressure), which were also associated with hypertension (p=0.042 and p=6.3×10^?3, respectively). Further, 3 SNPs were associated with hypertension (p=0.042 for rs7902529, p=0.027 for rs10135446, and p=0.01 for rs4613079) but not with blood pressure. Based on the moderate association signals and the low proportion of positive signals, this cross validation between African-Americans and Asians suggests that association studies of blood pressure traits require a larger number of subjects and a more refined design.     

Combined effects of hypertension and conditioning on coronary vascular reserve in rats

To evaluate the combined effects of cardiac overload imposed by hypertension and chronic swim training on coronary vascularity, female rats were made hypertensive by unilateral renal artery stenoses and were exercised in an 8- to 10-wk swimming program. Maximal coronary flow was assessed in isolated retrograde buffer-perfused hearts under conditions of minimal coronary resistance (15 microM adenosine or anoxia). Sedentary normotensive animals, sedentary hypertensive animals, and normotensive animals exposed to a swimming program were also studied. Swimming was associated with an 18% increase in heart weight and with increases in both absolute (ml/min) and relative (ml X g-1 X min-1) maximal coronary flow. Hypertension was associated with a 32% increase in heart weight but with a decrease in absolute and relative coronary flow compared with controls. The combined stimuli resulted in a 63% myocardial hypertrophy and a 19% increase in absolute flow. Relative coronary flow (g tissue-1) was similar in hearts from hypertensive sedentary animals and hypertensive swimmers. These data indicate that the coronary vascular deficit that accompanies the cardiac hypertrophy of hypertension is not worsened by the superimposition of an exercise load that exaggerates the hypertrophy.     

Admixture mapping provides evidence of association of the VNN1 gene with hypertension

Migration patterns in modern societies have created the opportunity to use population admixture as a strategy to identify susceptibility genes. To implement this strategy, we genotyped a highly informative ancestry marker panel of 2270 single nucleotide polymorphisms in a random population sample of African Americans (N = 1743), European Americans (N = 1000) and Mexican Americans (N = 581). We then examined the evidence for over-transmission of specific loci to cases from one of the two ancestral populations. Hypertension cases and controls were defined based on standard clinical criteria. Both case-only and case-control analyses were performed among African Americans. With the genome-wide markers we replicated the findings identified in our previous admixture mapping study on chromosomes 6 and 21 [1]. For case-control analysis we then genotyped 51 missense SNPs in 36 genes spaced across an 18.3 Mb region. Further analyses demonstrated that the missense SNP rs2272996 (or N131S) in the VNN1 gene was significantly associated with hypertension in African Americans and the association was replicated in Mexican Americans; a non-significant opposite association was observed in European Americans. This SNP also accounted for most of the evidence observed in the admixture analysis on chromosome 6. Despite these encouraging results, susceptibility loci for hypertension have been exceptionally difficult to localize and confirmation by independent studies will be necessary to establish these findings.     

Genome-Wide Association Study of Young-Onset Hypertension in the Han Chinese Population of Taiwan

Young-onset hypertension has a stronger genetic component than late-onset counterpart; thus, the identification of genes related to its susceptibility is a critical issue for the prevention and management of this disease. We carried out a two-stage association scan to map young-onset hypertension susceptibility genes. The first-stage analysis, a genome-wide association study, analyzed 175 matched case-control pairs; the second-stage analysis, a confirmatory association study, verified the results at the first stage based on a total of 1,008 patients and 1,008 controls. Single-locus association tests, multilocus association tests and pair-wise gene-gene interaction tests were performed to identify young-onset hypertension susceptibility genes. After considering stringent adjustments of multiple testing, gene annotation and single-nucleotide polymorphism (SNP) quality, four SNPs from two SNP triplets with strong association signals (−log₁₀(p)>7) and 13 SNPs from 8 interactive SNP pairs with strong interactive signals (−log₁₀(p)>8) were carefully re-examined. The confirmatory study verified the association for a SNP quartet 219 kb and 495 kb downstream of LOC344371 (a hypothetical gene) and RASGRP3 on chromosome 2p22.3, respectively. The latter has been implicated in the abnormal vascular responsiveness to endothelin-1 and angiotensin II in diabetic-hypertensive rats. Intrinsic synergy involving IMPG1 on chromosome 6q14.2-q15 was also verified. IMPG1 encodes interphotoreceptor matrix proteoglycan 1 which has cation binding capacity. The genes are novel hypertension targets identified in this first genome-wide hypertension association study of the Han Chinese population.     

OPRM1 and EGFR contribute to skin pigmentation differences between Indigenous Americans and Europeans

Contemporary variation in skin pigmentation is the result of hundreds of thousands years of human evolution in new and changing environments. Previous studies have identified several genes involved in skin pigmentation differences among African, Asian, and European populations. However, none have examined skin pigmentation variation among Indigenous American populations, creating a critical gap in our understanding of skin pigmentation variation. This study investigates signatures of selection at 76 pigmentation candidate genes that may contribute to skin pigmentation differences between Indigenous Americans and Europeans. Analysis was performed on two samples of Indigenous Americans genotyped on genome-wide SNP arrays. Using four tests for natural selection--locus-specific branch length (LSBL), ratio of heterozygosities (lnRH), Tajima's D difference, and extended haplotype homozygosity (EHH)--we identified 14 selection-nominated candidate genes (SNCGs). SNPs in each of the SNCGs were tested for association with skin pigmentation in 515 admixed Indigenous American and European individuals from regions of the Americas with high ground-level ultraviolet radiation. In addition to SLC24A5 and SLC45A2, genes previously associated with European/non-European differences in skin pigmentation, OPRM1 and EGFR were associated with variation in skin pigmentation in New World populations for the first time.     

Complex Analysis of Urate Transporters SLC2A9, SLC22A12 and Functional Characterization of Non-Synonymous Allelic Variants of GLUT9 in the Czech Population: No Evidence of Effect on Hyperuricemia and Gout

Objective

Using European descent Czech populations, we performed a study of SLC2A9 and SLC22A12 genes previously identified as being associated with serum uric acid concentrations and gout. This is the first study of the impact of non-synonymous allelic variants on the function of GLUT9 except for patients suffering from renal hypouricemia type 2.

Methods

The cohort consisted of 250 individuals (150 controls, 54 nonspecific hyperuricemics and 46 primary gout and/or hyperuricemia subjects). We analyzed 13 exons of SLC2A9 (GLUT9 variant 1 and GLUT9 variant 2) and 10 exons of SLC22A12 by PCR amplification and sequenced directly. Allelic variants were prepared and their urate uptake and subcellular localization were studied by Xenopus oocytes expression system. The functional studies were analyzed using the non-parametric Wilcoxon and Kruskall-Wallis tests; the association study used the Fisher exact test and linear regression approach.

Results

We identified a total of 52 sequence variants (12 unpublished). Eight non-synonymous allelic variants were found only in SLC2A9: rs6820230, rs2276961, rs144196049, rs112404957, rs73225891, rs16890979, rs3733591 and rs2280205. None of these variants showed any significant difference in the expression of GLUT9 and in urate transport. In the association study, eight variants showed a possible association with hyperuricemia. However, seven of these were in introns and the one exon located variant, rs7932775, did not show a statistically significant association with serum uric acid concentration.

Conclusion

Our results did not confirm any effect of SLC22A12 and SLC2A9 variants on serum uric acid concentration. Our complex approach using association analysis together with functional and immunohistochemical characterization of non-synonymous allelic variants did not show any influence on expression, subcellular localization and urate uptake of GLUT9.     

Novel association in chromosome 4q27 region with rheumatoid arthritis and confirmation of type 1 diabetes point to a general risk locus for autoimmune diseases

Recently, association of celiac disease with common single-nucleotide polymorphism (SNP) variants in an extensive linkage-disequilibrium block of 480 kb containing the KIAA1109, Tenr, IL2, and IL21 genes has been demonstrated in three independent populations (rs6822844 P_combined=1.3×10^-14). The KIAA1109/Tenr/IL2/IL21 block corresponds to the Idd3 locus in the nonobese diabetic mouse model of type 1 diabetes (T1D). This block was recently found to be associated with T1D in a genomewide association study, although this finding lacks unequivocal confirmation. We therefore aimed to investigate whether the KIAA1109/Tenr/IL2/IL21 region is involved in susceptibility to multiple autoimmune diseases. We tested SNP rs6822844 for association with disease in 350 T1D-affected and 1,047 rheumatoid arthritis (RA)–affected Dutch patients and in 929 controls. We replicated the association with T1D (P=.0006; OR 0.64 [95% CI 0.50–0.83]), and revealed a similar novel association with RA (P=.0002; OR 0.72 [95% CI 0.61–0.86]). Our results replicate and extend the association found in the KIAA1109/Tenr/IL2/IL21 gene region with autoimmune diseases, implying that this locus is a general risk factor for multiple autoimmune diseases.     

SLC1A2 Variant Is Associated with Essential Tremor in Taiwanese Population

Essential tremor (ET), which is one of the most common movement disorders, may lead to severe interference in quality of life. The first genome-wide association study (GWAS) has identified an association of the LINGO1 variant (rs9652490) with ET in Americans and Europeans. Recently, a second GWAS that was performed in a European population has discovered a new variant (rs3794087) of the main glial glutamate transporter (SLC1A2) that increases the risk of ET with an odds ratio of about 1.4. SLC1A2 encodes for the major glial high-affinity glutamate reuptake transporter in the brain and is a potential ET susceptibility gene. Because replication in a different ethnic population is important for validating a finding, we conducted a case-control study to investigate the SLC1A2 variant in an Asian cohort with ET in Taiwan. A total of 542 subjects (273 ET patients and 269 controls) were included. The results showed that rs3794087 was associated with ET among the Taiwanese. The odds ratio was 1.37. Our results were similar to those of the second GWAS of ET in Europeans, and this confirms that SLC1A2 may be a good functional candidate gene for ET. A replication study in another independent population is of importance to validate this association.     

Minisatellite polymorphisms of the SLC6A19: susceptibility in hypertension

The SLC6A19 is a human homolog of B⁰AT1 that encodes a neutral amino acid transporter. We examined the distribution of VNTR (variable number of tandem repeats; minisatellites) and conducted polymorphic analysis of SCL6A19 isolated from the genomic DNA of controls and multi-generational families. The SLC6A19 was found to contain seven blocks of minisatellites, 3 of which (SLC6A19-MS1, -MS4, and -MS7) showed polymorphism and were found to be transmitted through meiosis following Mendelian inheritance in seven families. These minisatellite polymorphisms may be useful markers for paternity mapping and DNA fingerprinting. Furthermore, we conducted a case-control study in which genomic DNA from 400 controls and 205 cases with essential hypertension was compared. A statistically significant association was identified between rare SLC6A19-MS7 alleles and the occurrence of hypertension (odds ratio, 7.87; 95% confidence interval, 0.88-70.66; and p = 0.028). These findings suggest that the rare SLC6A19-MS7 allele may be a risk factor for hypertension.     

Glutathione S-transferase variants as risk factor for essential hypertension in Italian patients

Involvement of genetic polymorphisms in arterial hypertension has already been reported, including GST genes, with contrasting results. The present research evaluates the possible association between GST gene polymorphisms and essential hypertension (EH) in an Italian population sample. 193 hypertensive subjects and 210 healthy controls were recruited. Buccal cells were collected from each subject using an oral swab and DNA was extracted using the phenol:chloroform:isoamilic alcohol method. GST SNPs were determined using the PCR-RFLP method, while GST null polymorphisms were determined using a Multiplex PCR. Among GST polymorphisms, only the frequency of the GSTT1 null phenotype was significantly higher in hypertensive patients than in normotensive participants. GSTT1 null individuals were significantly associated with increased risk of hypertension [P < 0.001; adjusted OR 2.24 (1.43-3.50)]. In sex-based analysis, the risk was significantly higher in female hypertensives [P < 0.001; adjusted OR 3.25 (1.78-5.95)] but not in male subjects. This study analyzed all GST gene that, in other research, have been studied in relation to arterial hypertension and the GSTO polymorphisms, showing an association only with GSTT1. The results for the GSTO genes represent the first analysis of this GST class in relation to blood pressure regulation. The association between the GSTT1 null phenotype and EH was confirmed in the overall population and in women, but not in men. These data suggest that GSTT1 could be a sex-specific candidate gene for EH.     

Calpastatin level in spontaneously hypertensive rats

We studied calpastatin activity in erythrocytes of Milan hypertensive and prehypertensive rats, in their normotensive controls, in F1 and F2 hybrids, and in two inbred strains derived from F2, one hypertensive and the other normotensive. Our results show that the decrease in calpastatin activity observed in Milan hypertensive rats was not caused by hypertension, it was transmitted in a recessive way in heterozygous, and it was not correlated to hypertension.