Genome-wide linkage disequilibrium mapping of hypertension in Japan

Characterization of VNTRs Within the Entire Region of SLC6A3 and Its Association with Hypertension

The dopamine transporter SLC6A3 (DAT1) mediates uptake of dopamine into presynaptic terminals. In addition, in previous reports, hypertensive rats were associated with DAT gene, but the genetic association with SLC6A3 and hypertension is still unknown. We examined the distribution of variable number of tandem repeats (VNTRs) and conducted polymorphic analysis of the entire region of SLC6A3. Ten VNTR regions (MS1-10) were revealed throughout the intronic and UTRs; seven VNTR regions were newly isolated and three VNTRs were previously reported. Four VNTR regions (SLC6A3-MS1, -MS4, -MS8 [rs3836790], and -MS9 [rs28363170]) showed polymorphism and these loci were found to be transmitted through meiosis following Mendelian inheritance. These VNTR polymorphisms may be useful markers for paternity mapping and DNA fingerprinting. Furthermore, we also conducted a case-control study between the controls and essential hypertensive cases. Analysis of the genotypes of SLC6A3-MS8 (rs3836790) revealed that having an 8/6-repeat allele, which was only detected in hypertensive cases, was associated with hypertension (p < 0.05). Additional significant association was identified between the short 7-repeat allele of SLC6A3-MS9 (rs28363170) and the occurrence of hypertension (odds ratio 2.02; p < 0.05). These results revealed the genetic association between SLC6A3 and hypertension, and the specific VNTR alleles of SLC6A3 may be a risk factor for hypertension.

1H NMR-based metabonomic analysis of urine from young spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and their substrains are a useful model for studying essential hypertension which is a complex, polygenic, and multifactorial disorder. Their genetic and metabolic features are of great interest because they may provide insights into the mechanism of blood pressure regulation. We have compared urinary metabolic profiles of young SHR with those of their age-matched normotensive controls, Wistar Kyoto rats, using (1)H NMR-based metabonomics. Principal components analysis was applied to the NMR spectral data after data-reduced and normalized by the total integral or the creatinine integral. Consequently, a clear separation of urine samples between the two strains was observed in the principal components scores plot. The loadings plot from the data normalized by the creatinine integral showed that many metabolites such as citrate, alpha-ketoglutarate, and hippurate contributed to the separation, and the urinary levels of most metabolites used in this study, including these three, were lower in SHR than in Wistar Kyoto rats. These metabolic changes may be concerned with blood pressure regulation in SHR, although a relation to other strain differences cannot be ruled out. The present study suggests the usefulness of a (1)H NMR-based metabonomic approach using SHR in the field of hypertension research.

A nonsense polymorphism (Y319X) of the solute carrier family 6 member 18 (SLC6A18) gene is not associated with hypertension and blood pressure in Japanese

We investigated the possible association of solute carrier family 6 member 18 (SLC6A18) with hypertension and blood pressure in Japanese, since the homologous murine XT2 gene was recently reported to be associated with hypertension. The entire coding region of SLC6A18 was sequenced in 30 unrelated Japanese subjects. The deleterious effects of the observed nonsynonymous single nucleotide polymorphisms (SNPs) on the phenotype were predicted using bioinformatics software. We tested the associations of one deleterious SNP (Y319X) with blood pressure and hypertension in a general population of 1,004 subjects in one area of Japan. Both quantitative and qualitative analyses adjusting for age and body mass index (BMI) as covariates were undertaken. Four synonymous (P7P, T32T, G37G and V387V), three missense (S12C, I32T and L478P) and one nonsense (Y319X: g1230757 C > G) polymorphisms were found. One of the synonymous polymorphisms was novel (V387V) by reference to the dbSNP database. The Y319X genotype distribution of CC:CG:GG in this population showed frequencies of 0.382, 0.461 and 0.156, respectively, which followed Hardy-Weinberg equilibrium. The nonsense polymorphism had odds ratios of 0.83 (confidence interval [CI] = 0.59-1.15, p = 0.26) in males and 0.96 (CI = 0.72-1.29, p = 0.80) in females with hypertension or current medication for hypertension. For the quantitative analysis, we excluded the current medication subgroup. The nonsense allele was not a significant predictor for systolic or diastolic blood pressure. This is the first report showing that a single polymorphism in SLC6A18 is not associated with hypertension or blood pressure in Japanese.

An association of 5,10-Methylenetetrahydrofolate Reductase (MTHFR) gene polymorphism and ischemic stroke

Plasma homocysteine (Hcy) concentration has been shown to be influenced by a mutation in the gene coding methylenetetrahydrofolate reductase (MTHFR). Although plasma Hcy has been shown to be related to atherosclerotic disorders, the association between MTHFR gene polymorphism and ischemic stroke remains controversial. In the present study we investigated the association between MTHFR gene polymorphism and risk factor-dependent augmentation for ischemic stroke in subjects with several risk factors for atherosclerosis, with special emphasis on the risk factor-gene interaction. The diagnosis of cerebral infarction in each patient was confirmed by computed tomography (CT) findings of the brain. MTHFR C677T polymorphism was genotyped with a conventional method. In 97 stroke patients (48 cases of atherothrombotic infarction, 38 cases of lacunar infarction, 9 cases of cardiac embolism, 2 others) and 241 age-and sex-matched healthy control subjects, the frequencies of the T allele were 0.44 and 0.39, respectively. In patients with CT-proven atherothrombotic infarction, the T allele frequency was 0.54 (P = .033 vs controls). The adjusted odds ratio in subjects with TT genotype for atherothrombotic infarction was 3.87 (95% confidence interval = 1.27-11.8). A general linear model analysis showed that an interaction between the HDL-C and MTHFR genotype was significantly associated with atherothrombotic infarction (F = 5.695; P = .018). These findings indicate that the T allele of the MTHFR gene is significantly associated with atherothrombotic infarction. Furthermore, the analysis of risk factor-gene interaction could be a useful tool for deriving specific predictive information about ischemic stroke in an elderly Japanese population.

Sympathetic Hypertensive Syndrome: A Possible Surgically Curable Type of Hypertension

Poorly controlled hypertension was incidentally cured after performing an endoscopic sympathetic block (ESB) in a patient with hyperhidrosis craniofacialis (HHC). A survey of the literature indicated that 30% to 40% of essential hypertension is of sympathetic origin. Patients with facial sweating associated with hypertension were then studied to determine whether blood pressure is lowered after performing ESB. Between November 2002 and July 2003, 17 hypertensive patients (13 males and 4 females) ranging in age from 22 to 62 years underwent ESB solely for HHC at the Department of Surgery of Kaohsiung Medical University, Taiwan. Their preoperative systolic blood pressure (SBP) values ranged from 170 +/- 6 to 200.7 +/- 7.6 mmHg, and their diastolic blood pressure (DBP) values ranged from 94.7 +/- 6.1 to 120.3 +/- 5.7 mmHg. Their heart rates were between 92.67 +/- 2.28 and 119.67 +/- 5.13 beats per minute (bpm). They were refractory to aggressive medical treatment, including lifestyle modifications and antihypertensive medications. Their postoperative blood pressure, heart rate and surgical outcomes were recorded. After performing ESB, HHC was cured in all 17 patients. Based on the reductions in blood pressure and heart rate, the patients could be divided into two groups, one showing high-level reductions (Group T) and one showing low-level reductions (Group S). The blood pressure of Group T (ten patients) was reduced to the range of 120.2 +/- 6.9 to 131.6 +/- 3.5 mmHg SBP and 74.8 +/- 3.1 to 85.4 +/- 4.5 DBP, and the heart rate of this group was reduced to the range of 65.36 +/- 4.63 to 85 +/- 3.60 bpm, while the blood pressure and heart rate of Group S (seven other patients) were reduced to the ranges of 145.9 +/- 5.7 to 160.5 +/- 5.5 mmHg SBP, 90 +/- 4 to 100.7 +/- 3.2 mmHg DBP, and 80 +/- 4 to 90.83 +/- 3.53 bpm, respectively. The patients in Group S were well controlled at 119.8 +/- 5.5 to 130.6 +/- 8.0 mmHg SBP and 70.1 +/- 3.8 to 84.5 +/- 5.7 mmHg DBP with a daily low-dose of calcium channel blocker. The average follow-up periods of the two groups were 17.00 +/- 2.906 and 17.43 +/- 2.37 months, respectively. We named this surgically curable form of hypertension "Sympathetic Hypertensive Syndrome" (SHS), which we define by the presence of all three of the following: 1) stage II hypertension; 2) HHC or other sympathetic disorders; and 3) heart rate > or = 100 bpm. If the patient is male the reductions of blood pressure after the surgery will be better, which might be due to the link with Y chromosome. Finally, we recommend that ESB should be performed in patients with SHS, although the female would respond less satisfactorily in terms of the blood pressure.

Investigations into Biochemical Changes of Genetic Hypertensive Rats Using 1H Nuclear Magnetic Resonance-Based Metabonomics

Genetically hypertensive rats provide a simple and accessible model for studying essential hypertension, which is a polygenic, heterogenous and multifactorial disease. Their genetic and metabolic features are of great interest because they may provide insight into the pathophysiological processes underlying essential hypertension. We have investigated the genetic influence on metabolic balance and metabolite excretion patterns in stroke-prone spontaneously hypertensive rats (SHRSP) with established hypertension using 1H NMR-based metabonomics. Urinary metabolite profiles for SHRSP and their age-matched normotensive controls, Wistar Kyoto rats, were acquired using 1H NMR spectroscopy. Principal components analysis was applied to these complex NMR data to facilitate differentiation and determine metabolic differences between urine samples collected from the hypertensive and normotensive rats. Consequently, it was possible to distinguish urine samples between the two strains in the principal components scores plot. The loadings plot showed that taurine, creatine and some unidentified metabolites resonating at around delta 2.48, 3.10 and 3.58 predominantly contributed to the separation. In SHRSP, the urinary levels of taurine and creatine were found to be higher and the intensities of the unknown signals much lower than those in the Wistar Kyoto rats. Although the pathophysiological significance of these components remains to be elucidated, this study suggests that 1H NMR-based metabonomics is a promising approach to provide new information on metabolic changes related to the pathophysiological processes of the genetically hypertensive rats.