Emanuela Bulla

Association of ATP1A1 and Dear Single-Nucleotide Polymorphism Haplotypes With Essential Hypertension Sex-Specific and Haplotype-Specific Effects

Essential hypertension remains a major risk factor for cardiovascular and cerebrovascular diseases. As a complex multifactorial disease, elucidation of susceptibility loci remains elusive. ATP1A1 and Dear are candidate genes for 2 closely linked rat chromosome-2 blood pressure quantitative trait loci. Because corresponding human syntenic regions are on different chromosomes, investigation of ATP1A1 (chromosome [chr]-1p21) and Dear (chr-4q31.3) facilitates genetic analyses of each blood pressure quantitative trait locus in human hypertension. Here we report the association of human ATP1A1 (P<0.000005) and Dear (P<0.03) with hypertension in a relatively isolated, case/control hypertension cohort from northern Sardinia by single-nucleotide polymorphism haplotype analysis. Sex-specific haplotype analyses detected stronger association of both loci with hypertension in males than in females. Haplotype trend-regression analyses support ATP1A1 and Dear as independent susceptibility loci and reveal haplotype-specific association with hypertension and normotension, thus delineating haplotype-specific subsets of hypertension. Although investigation in other cohorts needs to be performed to determine genetic effects in other populations, haplotype subtyping already allows systematic stratification of susceptibility and, hence, clinical heterogeneity, a prerequisite for unraveling the polygenic etiology and polygene–environment interactions in essential hypertension. As hypertension susceptibility genes, coexpression of ATP1A1 and Dear in both renal tubular cells and vascular endothelium suggest a cellular pathogenic scaffold for polygenic mechanisms of hypertension, as well as the hypothesis that ATP1A1 and/or Dear could contribute to the known renal and vascular endothelial dysfunction associated with essential (polygenic) hypertension.

Haplotypes of the adrenergic system predict the blood pressure response to β-blockers in women with essential hypertension

AIMS To analyze the association of haplotypes of the adrenergic system with essential hypertension and with the blood pressure response to beta-blockers. MATERIALS & METHODS In 1112 never-treated essential hypertension patients and 203 normotensive controls, tightly linked SNPs of beta-adrenergic receptors (ADRB1 - Ser49Gly and Arg389Gly; ADRB2 - Cys19Arg, Gly16Arg and Gln27Glu) and the G-protein beta3-subunit (GNB3 - A3882C, G5249A and C825T) were genotyped. Association of haplotypes with essential hypertension and with the blood pressure response to atenolol 50 mg twice daily in a subgroup of essential hypertension patients (n = 340) was evaluated (Haploview 3.2). RESULTS No SNPs or haplotypes were associated with essential hypertension. In females only, GNB3 SNPs and haplotypes were associated with the blood pressure response (p < 0.05). CONCLUSION Our study confirmed the sex-specific association of GNB3 with the blood pressure response to atenolol with no substantial advantage of the analysis of haplotypes over SNPs.

Clinical variables, not RAAS polymorphisms, predict blood pressure response to ACE inhibitors in Sardinians

AIM No definite factors predict blood pressure response to angiotensin-converting enzyme-inhibitors. The aim of this study was to test the association of gene polymorphisms of the renin-angiotensin-aldosterone system with essential hypertension and anthropometric variables, intermediate phenotypes and gene polymorphisms with blood pressure after fosinopril in a genetically homogeneous cohort. METHODS A total of 630 essential hypertension patients, not previously treated or out of antihypertensive treatment for at least 6 months versus 219 normotensives (genotype frequencies, chi(2)). A total of 191 patients were randomly assigned to fosinopril 20 mg/day. Samples for plasma renin activity and aldosterone, 24-h urinary sodium (flame photometry) were collected. Gene polymorphisms--angiotensin-converting enzyme (insertion/deletion), angiotensin II type 1-receptor (A1166C), aldosterone synthase (-344C/T) and angiotensinogen (-6A/G)--were analyzed by standard techniques. The association of anthropometric variables, intermediate phenotypes and gene polymorphisms with blood pressure after 4 weeks therapy was tested by univariate analysis and analysis of covariance model (Intercooled Stata SE 9.2). RESULTS No genetic polymorphisms were associated with essential hypertension, blood pressure response and intermediate phenotypes (p > 0.05). Systolic blood pressure after therapy was associated with baseline systolic blood pressure, age and sex. CONCLUSIONS Our results confirm the difficulty in dissecting both essential hypertension and pharmacogenomics when analyzing the effect of single genes in complex multifactorial traits.

Prevalence and clinical features of heterozygous carriers of autosomal recessive hypercholesterolemia in Sardinia

OBJECTIVE Autosomal recessive hypercholesterolemia (ARH) is a lipid disorder caused by mutations in a specific adaptor protein for the LDL receptor. ARH is rare except in Sardinia where three alleles (ARH1, ARH2 and ARH3) explain most of cases. The prevalence of ARH heterozygotes in Sardinia is not well determined as well as inconclusive data are available on the effect of the ARH carrier status on LDL cholesterol (LDL-C) and coronary risk. METHODS 3410 Sardinians (986 blood donors, 1709 with hypertension and 715 with myocardial infarction (MI)) were screened for ARH alleles. For comparison purposes, lipid data of 60 ARH heterozygous carriers and 60 non-carriers identified within 24 ARH families were also considered. RESULTS In the whole study cohort, no ARH homozygotes were found, but 15 ARH1 (0.44%) and 9 ARH2 (0.26%) heterozygous carriers were identified. The frequency of ARH alleles in blood donors was 0.0030, not different from that in hypertensive subjects (0.0032). ARH alleles tended to be more common in MI patients (0.0049), but no association between ARH carrier status and MI risk was detected after controlling for conventional risk factors. ARH carriers and non-carriers showed similar LDL-C levels. This result was confirmed when ARH carriers and non-carriers identified throughout family-based and population-based screenings were combined and compared (141.0+/-41 mg/dl vs. 137.0+/-41 mg/dl, respectively; p=0.19). CONCLUSIONS These data indicate that the frequency of ARH heterozygotes in Sardinia is approximately 1:143 individuals, thus making this condition one of the most common in the Sardinian population. However, ARH carrier status does not influence LDL-C concentration and coronary risk, thus suggesting that ARH can be regarded as a truly recessive disorder.

Genome-wide association study identifies CAMKID variants involved in blood pressure response to losartan: the SOPHIA study

BACKGROUND Essential hypertension arises from the combined effect of genetic and environmental factors. A pharmacogenomics approach could help to identify additional molecular mechanisms involved in its pathogenesis. AIM The aim of SOPHIA study was to identify genetic polymorphisms regulating blood pressure response to the angiotensin II receptor blocker, losartan, with a whole-genome approach. MATERIALS & METHODS We performed a genome-wide association study on blood pressure response in 372 hypertensives treated with losartan and we looked for replication in two independent samples. RESULTS We identified a peak of association in CAMK1D gene (rs10752271, effect size -5.5 ± 0.94 mmHg, p = 1.2 × 10(-8)). CAMK1D encodes a protein that belongs to the regulatory pathway involved in aldosterone synthesis. We tested the specificity of rs10752271 for losartan in hypertensives treated with hydrochlorothiazide and we validated it in silico in the GENRES cohort. CONCLUSION Using a genome-wide approach, we identified the CAMK1D gene as a novel locus associated with blood pressure response to losartan. CAMK1D gene characterization may represent a useful tool to personalize the treatment of essential hypertension.

Conceptual basis and methodology of the SOPHIA study

To clarify the role of gene polymorphisms on the effect of losartan and losartan plus hydrochlorothiazide on blood pressure (primary end point) and on cardiac, vascular and metabolic phenotypes (secondary end point) after 4, 8, 12, 16 and 48 weeks treatment, an Italian collaborative study - The Study of the Pharmacogenomics in Italian hypertensive patients treated with the Angiotensin receptor blocker losartan (SOPHIA) - on never-treated essential hypertensives (n = 800) was planned. After an 8 week run-in, losartan 50 mg once daily will be given and doubled to 100 mg at week +4 if blood pressure is more than 140/90 mmHg. Hydroclorothiazide 25 mg once daily at week +8 and amlodipine 5 mg at week +16 will be added if blood pressure is more than 140/90 mmHg. Cardiac mass (echocardiography), carotid intima-media thickness, 24 h ambulatory blood pressure, homeostatic model assessment (HOMA) index, microalbuminuria, plasma renin activity and aldosterone, endogenous lithium clearance, brain natriuretic peptide and losartan metabolites will be evaluated. Genes of the renin-angiotensin-aldosterone system, salt sensitivity, the beta-adrenergic system and losartan metabolism will be studied (Illumina custom arrays). A whole-genome scan will also be performed in half of the study cohort (1M array, Illumina 500 GX beadstation).

Integrating the Pathophysiology and Pharmacogenomics of Essential Hypertension

The results of pharmacogenomics studies on essential hypertension are contrasting. Methodological flaws in study design, patient selection, statistics and analysis may be responsible for these discrepancies. In this article we review the literature on the pharmacogenomics of essential hypertension and provide suggestions for future pharmagenomic studies.