The Genetic Basis of Hypertension

Hypertension (HTN) is one of the major risk factors for almost all cardiovascular diseases including coronary artery disease, stroke, heart failure and renal failure. Nonetheless , blood pressure (BP) regulation is insufficient due to its multifactorial nature involving interactions among genetic, environmental, mechanistic and neuroendocrine factors. Essential hypertension is the most frequent diagnosis indicating that a monocausal etiology has not been identified. The identification of causal genetic determinants has been unfulfilling. Analyses of rare monogenic syndromes of HTN focusing on renal sodium handling and steroid hormone metabolism have proved the well-defined genetic frame of hypertension though they do not affect the normal distribution of BP in the general population. Genome-wide association studies (GWAS) have revealed genetic variants that are associated with BP with small effect size which cumulatively explain to a very small extend the variability of BP. New large-scale studies in the genomic arena will clarify the polygenic determinants of BP and open a perspective on translation of the progression in BP genetics to clinical use

Nondipping Blood Pressure: Predictive or Reactive Failure of Renal Sodium Handling?

Blood pressure follows a daily rhythm, dipping during nocturnal sleep in humans. Attenuation of this dip (nondipping) is associated with increased risk of cardiovascular disease. Renal control of sodium homeostasis is essential for long-term blood pressure control. Sodium reabsorption and excretion have rhythms that rely on predictive/circadian as well as reactive adaptations. We explore how these rhythms might contribute to blood pressure rhythm in health and disease.

Renal Sodium Handling in Relation to Environmental and Genetic Factors in Untreated Chinese

Background We investigated proximal and distal renal tubular sodium handling, as assessed by fractional excretion of lithium (FELi) and fractional distal reabsorption rate of sodium (FDRNa), in relation to environmental and genetic factors in untreated patients. Methods Our study participants were suspected hypertensive patients being off antihypertensive medication for ≥2 weeks and referred for 24-hour ambulatory blood pressure monitoring. We collected serum and 24-hour urine for measurement of sodium, creatinine and lithium concentration, and calculated FELi and FDRNa. We genotyped 19 SNPs associated with renal sodium handling or blood pressure using the ABI SNapShot method. Results The 1409 participants (664 men, 47.1%) had a mean (±SD) age of 51.0±10.5 years. After adjustment for host factors, both FELi and FDRNa were significantly (P≤0.01) associated with season and humidity, explaining ~1.3% and ~3.5% of the variance, respectively. FELi was highest in autumn and lowest in summer and intermediate in spring and winter (P=0.007). FDRNa was also highest in autumn but lowest in winter and intermediate in spring and summer (P<0.001). Neither FELi nor FDRNa was associated with outdoor temperature or atmospheric pressure (P≥0.13). After adjustment for host and environmental factors and Bonferroni multiple testing, among the 19 studied genetic variants, only rs12513375 was significantly associated with FELi and FDRNa (P≤0.004) and explained about 1.7% of the variance. Conclusions Renal sodium handling as measured by endogenous lithium clearance was sensitive to major environmental and genetic factors. Our finding is towards the use of these indexes for the definition of renal tubular dysfunction.

The Genetic Basis of Hypertension

Hypertension (HTN) is one of the major risk factors for almost all cardiovascular diseases including coronary artery disease, stroke, heart failure and renal failure. Nonetheless , blood pressure (BP) regulation is insufficient due to its multifactorial nature involving interactions among genetic, environmental, mechanistic and neuroendocrine factors. Essential hypertension is the most frequent diagnosis indicating that a monocausal etiology has not been identified. The identification of causal genetic determinants has been unfulfilling. Analyses of rare monogenic syndromes of HTN focusing on renal sodium handling and steroid hormone metabolism have proved the well-defined genetic frame of hypertension though they do not affect the normal distribution of BP in the general population. Genome-wide association studies (GWAS) have revealed genetic variants that are associated with BP with small effect size which cumulatively explain to a very small extend the variability of BP. New large-scale studies in the genomic arena will clarify the polygenic determinants of BP and open a perspective on translation of the progression in BP genetics to clinical use.

Sex and Body Mass Index Modify the Association Between Leptin and Sodium Excretion: A Cross-sectional Study in an African Population

BACKGROUND Renal sodium handling could be a potential mediator linking adipokines to hypertension. The aim of the study was to assess the relationship of leptin with urinary sodium excretion and proximal sodium reabsorption in humans. METHODS This cross-sectional study was conducted on participants of hypertensive families from the Seychelles Island. A split urine (daytime and nighttime) collection and plasma leptin were measured. Endogenous lithium clearance was used to assess proximal sodium reabsorption. Mixed multiple linear regression tests adjusted for confounding factors were used. RESULTS Three hundred and sixty-five participants (57% women) were included in this analysis. Leptin and adiponectin were higher in women (P < 0.001). Leptin was associated positively with daytime (coefficient [c]: 0.16, standard deviation (SD): 0.03, P < 0.001), nighttime urinary sodium excretion (c: 0.17, SD: 0.04), P < 0.01), daytime lithium clearance (c: 0.40, SD: 0.08, P < 0.001), and nighttime lithium clearance (c: 0.39, SD: 0.10, P < 0.001) after adjusting for sex. The association was lost or mitigated only when BMI was introduced in the model. When BMI was categorized in normal vs. overweight participant, leptin was associated with daytime and nighttime sodium excretion rates (c: 0.14, SD: 0.05, P = 0.011 and c: 0.22, SD: 0.07, P = 0.002, respectively) only in overweight participants. CONCLUSION Leptin is associated positively with daytime and nighttime sodium excretion and lithium clearance suggesting a natriuretic rather than a sodium retaining effect of leptin. Sex and body mass index (BMI) are major confounders in this association. These results highlight the importance of sex and obesity in our understanding of the relationships between leptin, blood pressure, and renal sodium handling.