High Urinary Calcium Excretion and Genetic Susceptibility to Hypertension and Kidney Stone Disease

Urinary Calcium Is Associated with Serum Sclerostin among Stone Formers

BACKGROUND

Sclerostin plays an important role in bone metabolism and adipose tissue. Animal studies suggest that sclerostin influences urinary calcium (UCa), but this relationship has not been evaluated in stone formers (SFs). We aimed to investigate the association of UCa with serum sclerostin, bone mineral density (BMD), and body composition among SFs.

METHODS

Clinical and laboratorial data were retrieved from medical records. Determinants of UCa were studied using linear regression.

RESULTS

A total of 107 SFs (35.8 ± 9.3 years, 54% male) with eGFR 99.8 ± 14.5 mL/min/1.73 were studied. Subjects were split by sex and grouped into tertiles of UCa levels. Men in the highest UCa tertile had higher body mass index (BMI) and serum sclerostin, lower lean mass, and a trend towards higher fat mass. Women in the highest tertile had higher BMI and a trend towards higher serum sclerostin. Hypertension and metabolic syndrome, but not lower BMD, were more prevalent in the highest UCa tertile for both sexes. Sclerostin was positively correlated with fat mass and inversely correlated with lean mass among men, but not among women. BMD corrected for BMI at lumbar spine was inversely associated with UCa in a univariate analysis, but only serum sclerostin, hypertension, and NaCl intake were independent determinants of UCa in the multivariate model.

CONCLUSION

The present findings disclose that in addition to hypertension and salt intake, serum sclerostin is associated with urinary calcium in stone formers, suggesting that in addition to the hormones traditionally thought to alter calcium reabsorption in the kidney, sclerostin may play a significant additional role, warranting further investigation.

Nephrolithiasis: A Red Flag for Cardiovascular Risk

Epidemiological evidence shows that nephrolithiasis is associated with cardiovascular (CV) morbidities. The association between nephrolithiasis and CV disease is not surprising because both diseases share conditions that facilitate their development. Metabolic conditions, encompassed in the definition of metabolic syndrome (MS), and habits that promote nephrolithiasis by altering urine composition also promote clinical manifestations of CV disease. By inducing oxidative stress, these conditions cause endothelial dysfunction and increased arterial stiffness, which are both well-known predictors of CV disease. Furthermore, the subtle systemic metabolic acidosis observed in stone formers with CV disease may have a pathogenic role by increasing bone turnover and leading to reduced mineral content and osteoporosis/osteopenia. Heart valves and/or coronary artery and aortic calcifications are frequently associated with reduced mineral density. This is known as the 'calcification paradox' in osteoporosis and has also been observed in subjects with calcium nephrolithiasis. Evidence supports the hypothesis that osteoporosis/osteopenia is an independent risk factor for the development of CV calcifications. In the long term, episodes of renal stones may occur from the onset of metabolic derangements/MS to arterial stiffness/atherosclerosis and CV morbidities. These episodes should be considered a warning sign of an ongoing and silent atherosclerotic process. The evaluation of cardiometabolic risk factors and MS components should be routine in the assessment of renal stone formers. This would allow for treatment and prevention of the development of CV complications, which are much more severe for the patient and for public health.

The new patterns of nephrolithiasis: What has been changing in the last millennium?

Nephrolithiasis has been increasing over the last millennium. Although early epidemiologic studies have shown that kidney stones were two to three times more frequent in males than in females, recent reports have suggested that this rate is decreasing. In parallel a dramatic increase of nephrolithiasis has also been observed among children and adolescents. Furthermore, epidemiologic studies have shown a strong association between metabolic syndrome (Mets) traits and kidney stone disease. Patients with hypertension have a higher risk of stone formation and stone formers are predisposed to develop hypertension compared to the general population. An incidence of nephrolithiasis greater than 75% has been shown in overweight and obese patients compared to those of normal weight. It has also been reported that a previous diagnosis of diabetes mellitus increases the risk of future nephrolithiasis. Additionally, an association between metabolic syndrome and uric acid stone formation has been clearly recognized. Furthermore, 24-h urinary metabolic abnormalities have been decreasing among patients with nephrolithiasis over the last decades. Finally, nephrolithiasis could cause chronic kidney disease (CKD) and end stage renal disease (ESRD), especially in women and overweight patients. According to these observations, a better understanding of these new features among stone former patients may be required. Hence, the recognition and the correction of metabolic disorders could help not only to reduce the primary disease, but also stone recurrence.

Associations between nephrolithiasis and diabetes mellitus, hypertension and gallstones: A meta-analysis of cohort studies

AIM

To review and clarify the strengths and directions of associations between nephrolithiasis and hypertension (HTN), diabetes mellitus (DM) and gallstones (GS) given the inconsistent results reported in cohort studies.

METHODS

Relevant literature was searched in PubMed and EMBASE from inception to July 2019, for cohort studies that examined the relationships between kidney stones and these three diseases among adults. Pooled relative risks (RRs) were calculated by maximally adjusted risk estimates using a random effect model. Subgroup analysis, meta-regression and sensitivity analysis were conducted whenever appropriate.

RESULTS

Of 3537 papers, 21 articles with each including 1 to 3 cohorts were identified. In this meta-analysis, nephrolithiasis was reciprocally linked to HTN, DM and GS. Kidney stones were significantly associated with 31%, 33% and 46% higher risks of incident HTN, DM and GS whereas GS was associated with a significantly higher risk of nephrolithiasis (RR: 1.49; 95% CI, 1.28-1.73), followed by HTN (RR: 1.30; 95% CI, 1.11-1.52) and DM (RR: 1.18; 95% CI, 1.07-1.29). Also, females with DM (RR: 1.29; 95% CI, 1.08-1.55) were more likely to develop kidney stones than diabetic male patients (RR: 0.91; 95% CI, 0.75-1.10).

CONCLUSION

Although additional studies are needed to confirm these findings and elucidate the mechanisms, this study revealed possible bidirectional associations between nephrolithiasis and HTN, diabetes and GS, which reinforced the notion of nephrolithiasis as a systemic disease that requires comprehensive investigations.

Anthropometric and Biochemical Predictors for Hypertension in a Cross-Sectional Study in Zanzibar, Tanzania

Background: Aim of this study was to describe the proportion of hypertension among Zanzibari of different age-groups and to detect possible correlates of this non-communicable disease.

Methods: In 2013 a cross-sectional survey was conducted in Unguja Island, Zanzibar. A total of 235 randomly selected households, including 1,229 (2 to 95 years) eligible study participants, were examined. Association between objectively assessed obesity markers, salt intake and hypertension were investigated. Estimates of 24 h sodium and potassium excretion from a single morning spot urine specimen were calculated and used as surrogate for salt intake. The association between overweight/obesity and hypertension in different age-groups was assessed in multilevel logistic regression models. Further associations between salt intake and hypertension were analyzed.

Results: Measures of systolic and diastolic blood pressure as well as proportion of overweight/obesity and hypertension both increased with age. Overweight and obesity were significantly associated with hypertension in adults. Moreover, thinness seems to be associated with hypertension as well. We observed a significantly reduced chance of hypertension for higher urinary sodium-to-potassium compared to a lower ratio in children.

Conclusion: Overweight/obesity and hypertension were highly prevalent (>47% of adults >40 years are overweight or obese and >69% are hypertensive in the same age group) in our sample. Weight status was confirmed as a correlate of high blood pressure in our sample from Zanzibar, Tanzania. To early and effectively prevent related severe cardiovascular outcomes, screening strategies but also monitoring strategies are required for this population.

Relations between dairy product intake and blood pressure: the INTERnational study on MAcro/micronutrients and blood Pressure

BACKGROUND

Epidemiologic evidence suggests that low-fat dairy consumption may lower risk of hypertension. Dairy products may be distinctly linked to health, because of differences in nutritional composition, but little is known about specific nutrients that contribute to the dairy-blood pressure (BP) association, nor to underlying kidney function.

METHODS

We examined cross-sectional associations to BP of dairy product intakes, total and by type, from the INTERnational study on MAcro/micronutrients and blood Pressure (INTERMAP) including 2694 participants aged 40-59 years from the UK and the USA. Eight BP, four 24-h dietary recalls and two 24-h urine samples were collected during four visits. Linear regression models adjusted for lifestyle/dietary factors to estimate BP differences per 2SD higher intakes of total-and-individual-types of dairy were calculated.

RESULTS

Multivariable linear regression coefficients were estimated and pooled. In contrast to total and whole-fat dairy, each 195 g/1000 kcal (2SD) greater low-fat dairy intake was associated with a lower SBP -2.31 mmHg and DBP -2.27 mmHg. Significant associations attenuated with adjustment for dietary phosphorus, calcium, and lactose, but strengthened with urinary calcium adjustment. Stratification by median albumin-creatinine ratio (ACR; high ACR indicates impaired kidney function) showed strong associations between low-fat dairy and BP in participants with low ACR (SBP: -3.66; DBP: -2.15 mmHg), with no association in participants with high ACR.

CONCLUSION

Low-fat dairy consumption was associated with lower BP, especially among participants with low ACR. Dairy-rich nutrients including phosphorus and calcium may have contributed to the beneficial associations with BP.

Clinical importance of chemokines and inflammatory cytokines for patient care following percutaneous nephrolithotripsy

Chemokines are a class of proteins with low molecular weight that serve important roles in the progression of inflammation. Percutaneous nephrolithotripsy is a surgical technique in which lasers or ultrasound are utilized to break down and/or remove kidney stones. In order to ensure a full recovery following surgery, effective patient care and nursing are required. In the present study, a total of 348 patients with kidney stones were recruited and the clinical importance of chemokines and inflammatory cytokines for the nursing of patients during perioperative period was investigated. Plasma levels of inflammatory cytokines, as well as chemokines in the C, CC and CXC families, were analyzed in patients following percutaneous nephrolithotripsy. Correlations between chemokines and inflammatory cytokines and the urinary concentration of calcium oxalate were also investigated. The results indicated that plasma levels of C and CC chemokines were downregulated in patients following percutaneous nephrolithotripsy, whereas the plasma concentrations of CXC chemokines were upregulated. Plasma concentration levels of inflammatory cytokines interleukin (IL)-8, IL-1, IL-17 and tumor necrosis factor (TNF)-α were significantly downregulated in patients following percutaneous nephrolithotripsy; however, no significant differences were observed in plasma levels of IL-6 and IL-10 pre- and post-surgery. Regression analysis revealed that plasma concentration levels of chemokine C motif ligand, which is a C chemokine, chemokine ligand 2, which is a CC chemokine, and TNF-α were positively correlated with the urinary concentration of calcium oxalate during the perioperative period. The results of the present study indicate that plasma levels of chemokines and inflammatory cytokines are clinically important for nursing of patients who experienced percutaneous nephrolithotripsy.

Risk of Hypertension among First-Time Symptomatic Kidney Stone Formers

BACKGROUND AND OBJECTIVES

Prior work has suggested a higher risk of hypertension in kidney stone formers but lacked disease validation and adjustment for potential confounders. Certain types of stone formers may also be at higher risk of hypertension.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In our study, incident symptomatic stone formers in Olmsted County from 2000 to 2011 were manually validated by chart review and age and sex matched to Olmsted County controls. We followed up patients through November 20, 2015. Hypertension was also validated by manual chart review, and the risk of hypertension in stone formers compared with controls was assessed both univariately and after adjusting for comorbidities. The risk of hypertension among different subtypes of stone formers was also evaluated.

RESULTS

Among 3023 coded stone formers from 2000 to 2011, a total of 1515 were validated and matched to 1515 controls (mean age was 45 years old, and 56% were men). After excluding those with baseline hypertension (20% of stone formers and 18% of controls), 154 stone formers and 110 controls developed hypertension. Median follow-up time was 7.8 years in stone formers and 9.6 years in controls. Stone formers were found to have a higher risk of hypertension compared with controls (hazard ratio, 1.50; 95% confidence interval, 1.18 to 1.92), even after adjusting for age, sex, body mass index, serum creatinine, CKD, diabetes, gout, coronary artery disease, dyslipidemia, tobacco use, and alcohol abuse (hazard ratio, 1.58; 95% confidence interval, 1.12 to 2.21). Results were similar after excluding patients who were ever on a thiazide diuretic (hazard ratio, 1.65; 95% confidence interval, 1.16 to 2.38). Stone composition, radiographic stone burden, number of subsequent stone events, and stone removal surgeries were not associated with hypertension (P>0.05 for all).

CONCLUSIONS

The risk of hypertension was higher after the first symptomatic kidney stone event. However, kidney stone severity, type, and treatment did not associate with hypertension.

The metabolic syndrome and urolithiasis: a systematic review and meta-analysis

PURPOSE

The aim of this study was to assess the association between metabolic syndrome (MetS) and urolithiasis.

BACKGROUND

Observational studies and reviews suggest an association between the incidence of urolithiasis and the prevalence of MetS. However, individual studies are needed to be gathered to come to a more reliable and precise conclusion.

METHODS

We searched the Pubmed-Medline and Embase databases up to February 2014 to identify studies related to urolithiasis and metabolic syndrome. Three authors independently extracted information on the study design, the characteristics of the study participants, exposure and outcome assessments, and the method used to control for potential confounding factors. A random-effects model was used for the risk estimates.

RESULTS

Five studies were included in the final analysis. Our meta-analysis of five cross-sectional controlled studies identified a significant association between urolithiasis and MetS, with an overall OR of 1.39 (1.14-1.70).

CONCLUSIONS

Patients with metabolic syndrome have an increased risk of having urolithiasis indicating that it should be assessed as a systemic disorder. However, these observations need to be evaluated using prospective, randomized studies.

The association of cardiovascular disease and metabolic syndrome with nephrolithiasis

PURPOSE OF REVIEW

This review describes the relationship between nephrolithiasis, vascular disease and metabolic syndrome.

RECENT FINDINGS

There is increasing evidence that kidney stone formation is associated with a number of systemic problems including cardiovascular disease, metabolic syndrome and its components. Some of these associations are bidirectional. The reasons for these associations are not totally clear, but potential factors include metabolic responses associated with these disorders that promote a stone forming milieu in urine, environmental factors such as diet, oxidative stress and inflammation and molecular changes impacting the transport of certain analytes in urine.

SUMMARY

Urologists need to be cognizant of these associations as they may be able to contribute to an early diagnosis of a significant medical problem, or provide counseling to patients to prevent their occurrence.

Risk factors associated with nephrolithiasis: a case-control study in China

Nephrolithiasis is a multifactorial disease. The authors conducted a case-control study in China to explore its associated risk factors. A total of 725 nephrolithiasis patients and 553 controls were asked to complete a questionnaire that asked for information about psychological, behavioral, and dietary factors along with a physical and blood biochemical examination. For men, higher education was negatively associated with nephrolithiasis (odds ratio [OR] = 0.6; 95% confidence interval [CI] = 0.4-1.0), whereas hypso-waist-to-hip ratio (hypso-WHR), defined as WHRs >0.9 for men and >0.8 for women (OR = 2.2; 95% CI = 1.4-3.4); overexercise (OR = 2.1; 95% CI = 1.3-3.5); and having experienced negative life events (OR = 2.2; 95% CI = 1.2-4.1) were positively associated with nephrolithiasis. For women, higher fluid intake was negatively associated with nephrolithiasis (OR = 0.6; 95% CI = 0.3-0.9), and abnormal status of blood pressure (BP) and blood lipids was positively associated with nephrolithiasis. Varied factors were related to differences in nephrolithiasis occurrence between genders. Besides taking enough fluids, maintaining a normal metabolic status, avoiding overexercise, and reducing BP might be beneficial in preventing nephrolithiasis.

Is oxidative stress, a link between nephrolithiasis and obesity, hypertension, diabetes, chronic kidney disease, metabolic syndrome?

Epidemiological studies have provided the evidence for association between nephrolithiasis and a number of cardiovascular diseases including hypertension, diabetes, chronic kidney disease, metabolic syndrome. Many of the co-morbidities may not only lead to stone disease but also be triggered by it. Nephrolithiasis is a risk factor for development of hypertension and have higher prevalence of diabetes mellitus and some hypertensive and diabetic patients are at greater risk for stone formation. An analysis of the association between stone disease and other simultaneously appearing disorders, as well as factors involved in their pathogenesis, may provide an insight into stone formation and improved therapies for stone recurrence and prevention. It is our hypothesis that association between stone formation and development of co-morbidities is a result of certain common pathological features. Review of the recent literature indicates that production of reactive oxygen species (ROS) and development of oxidative stress (OS) may be such a common pathway. OS is a common feature of all cardiovascular diseases (CVD) including hypertension, diabetes mellitus, atherosclerosis and myocardial infarct. There is increasing evidence that ROS are also produced during idiopathic calcium oxalate (CaOx) nephrolithiasis. Both tissue culture and animal model studies demonstrate that ROS are produced during interaction between CaOx/calcium phosphate (CaP) crystals and renal epithelial cells. Clinical studies have also provided evidence for the development of oxidative stress in the kidneys of stone forming patients. Renal disorders which lead to OS appear to be a continuum. Stress produced by one disorder may trigger the other under the right circumstances.

Causes of autonomic dysfunction in idiopathic recurrent kidney stone formers

BACKGROUND

A higher prevalence of hypertension and adverse cardiovascular outcomes has been reported in kidney stone formers (KSF). We performed this study with the purpose of evaluating the autonomic nervous system (ANS) activity in KSF.

METHODS

We performed a 70° head-up tilt test in 30 idiopathic recurrent KSF aged 45.6 ± 12.1 years old (17 men: 13 women) and 30 healthy controls aged 42.0 ± 12.4 years old (17 women: 13 men). Thirteen KSF were hypertensive, and 17 were normotensive. Blood pressure (BP) and heart rate variability (HRV) were used for the non-invasive assessment of the efferent activity of the ANS. Discrete wavelet transform (DWT) was used to quantify the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.4 Hz) components during several periods of tilt.

RESULTS

The results showed significantly higher HR and BP in KSF, in both supine and tilt positions. DWT revealed diminished HRV in the kidney stone patients during head-up tilt, with no increase in the LF and greater decrease in the HF components. The differences in the HF component of HRV were associated with obesity and hyperuricosuria, but the abnormalities of the LF component were independent of the explanatory variables. The LF component of systolic BP was significantly higher in KSF and was associated with hypertension.

CONCLUSIONS

Several factors may contribute to the presence of autonomic dysfunction in patients with recurrent nephrolithiasis. This abnormality has significant implications in cardiovascular risk assessment and treatment planning.

The genetic components of idiopathic nephrolithiasis

Nephrolithiasis is a cause of significant morbidity and medical care expenses worldwide. Its prevalence has increased steadily during the last three decades among both adults and children. This trend suggests that changing environmental factors play a significant role in the risk of developing kidney stones although, conversely, there are many indications that genes play an important role in this condition as well. A limited number of monogenic forms have been identified, but the majority of nephrolithiasis cases are the result of complex, multi-factorial interactions between genetic inheritance and environmental exposure. Scientific evidence indicates that inheritance accounts for about half of the risk of common forms, making these forms suitable for investigation by genetic analysis. Here, we review the numerous studies that have been conducted to establish the role of genes in determining the risk of nephrolithiasis, the differential contribution of genes to this risk, and the confounding influence that environmental variables have on genetic studies.

Association between metabolic syndrome and nephrolithiasis in an inpatient population in southern Italy: role of gender, hypertension and abdominal obesity

BACKGROUND

Metabolic syndrome (MetS) and nephrolithiasis (NL) are quite common disorders. While some of the components of MetS have been proposed as precursors of NL in population studies, no data are available about the possible association between NL and MetS as such. The primary objective of the study was to evaluate the relationship between MetS and NL. The secondary outcome was to examine the relationship between MetS single constitutive elements and NL considering the strict correlation occurring among these factors.

METHODS

We studied 2132 Caucasian inpatients of the 'Spinelli' Hospital in southern Italy (males/females = 0.95; mean age 63.8 +/- 15.8 years; body mass index 26.1 +/- 3.9 kg/m(2)). The MetS diagnosis was performed according to the Heart Association/National Heart, Lung, and Blood Institute criteria. The presence of NL was assessed by ultrasound examination of the kidneys and upper urinary tract.

RESULTS

Seven hundred twenty-five subjects (34.0%) had a positive diagnosis of MetS. Two hundred twenty subjects (10.3%) had echographic evidence of NL, while 199 subjects reported a past history of NL (9.3%). The presence of MetS, as well as the male sex, and the occurrence of a previous episode of NL (in male subjects only) were each independently related to echographic evidence of NL. Among the individual components of MetS, high blood pressure and abdominal obesity (in female individuals only) were also independently related to echographic evidence of NL.

CONCLUSIONS

MetS is significantly associated with echographic evidence of NL. A gender-related difference in the clinical expression of NL was also observed.

Increased acid excretion in kidney stone formers with essential hypertension

BACKGROUND

Although several studies have reported that kidney stone disease and hypertension are associated, the link between the two conditions has not been identified. This study investigated urinary excretion of different solutes, particularly citrate and acids, in kidney stone formers and examined their association with high blood pressure.

METHODS

The retrospective study included 234 consecutive subjects, aged 47.0 +/- 15.6, attending our metabolic clinic after episodes of kidney stones. Essential hypertension was present in 82 patients (35.0%). A difference in the urinary excretion of some of the investigated components was found between subjects with normal blood pressure and those with hypertension.

RESULTS

The results showed that hypertensive subjects were older and had a higher body mass index (BMI) and serum uric acid. They had a significantly lower urinary pH (5.6 +/- 0.4 versus 6.0 +/- 0.5) and citrate (2.55 +/- 1.36 versus 2.83 +/- 1.65 mmol/24 h), higher titratable acid (38.8 +/- 19.0 versus 26.8 +/- 15.0 mEq/24 h) and ammonium (41.6 +/- 17.6 versus 34.2 +/-12.4 mmol/24 h). Logistic regression analysis with the presence of hypertension as the dependent variable produced a model with the following predictors: age (P < 0.0001), BMI (P = 0.026), titratable acid (P = 0.025) and low urinary citrate level (P = 0.033). Urinary acid excretion increased with the stage of hypertension. No difference was found in the urinary excretion of other solutes.

CONCLUSIONS

These findings suggest that essential hypertension and acid excretion are linked in stone formers.

Oxalate in renal stone disease: the terminal metabolite that just won't go away

The incidence of calcium oxalate nephrolithiasis in the US has been increasing throughout the past three decades. Biopsy studies show that both calcium oxalate nephrolithiasis and nephrocalcinosis probably occur by different mechanisms in different subsets of patients. Before more-effective medical therapies can be developed for these conditions, we must understand the mechanisms governing the transport and excretion of oxalate and the interactions of the ion in general and renal physiology. Blood oxalate derives from diet, degradation of ascorbate, and production by the liver and erythrocytes. In mammals, oxalate is a terminal metabolite that must be excreted or sequestered. The kidneys are the primary route of excretion and the site of oxalate's only known function. Oxalate stimulates the uptake of chloride, water, and sodium by the proximal tubule through the exchange of oxalate for sulfate or chloride via the solute carrier SLC26A6. Fecal excretion of oxalate is stimulated by hyperoxalemia in rodents, but no similar phenomenon has been observed in humans. Studies in which rats were treated with (14)C-oxalate have shown that less than 2% of a chronic oxalate load accumulates in the internal organs, plasma, and skeleton. These studies have also demonstrated that there is interindividual variability in the accumulation of oxalate, especially by the kidney. This Review summarizes the transport and function of oxalate in mammalian physiology and the ion's potential roles in nephrolithiasis and nephrocalcinosis.

[Cardiovascular risk associated with urolithiasis]

OBJECTIVE

Urolithiasis appears to be associated with several cardiovascular risk factors (excess salt and animal proteins, hypertension, metabolic syndrome) and, more recently, the development of stroke. The authors describe the frequency of cardiovascular risk factors and cardiovascular events before and after management of urolithiasis.

METHOD

The authors retrospectively collected data from patients born before 1956 and managed surgically or instrumentally for urolithiasis in our establishment in 1994 concerning the frequency of cardiovascular risk factors and the incidence of acute coronary syndrome, stroke or acute lower limb ischaemia before or after treatment of urolithiasis.

RESULTS

Data were obtained for 33 patients, revealing 12 events including five previous events (four cases of acute coronary syndrome, one ischaemic stroke) and seven subsequent events (five cases of acute coronary syndrome with one death, one ischaemic stroke, one case of acute lower limb ischaemia) an average of 5.7 years after management. These 33 patients had an average of more than two risk factors.

CONCLUSION

This retrospective study based on a small sample size demonstrated a high frequency of risk factors and cardiovascular events. This correlation needs to be studied in more detail. Urolithiasis could constitute an indirect cardiovascular risk factor dependent on "classical" risk factors, suggesting the need for integrated management of stone patients, in the same way as for patients with erectile dysfunction.

The association of nephrolithiasis with hypertension and obesity: a review

Kidney stones affect hypertensive patients disproportionately compared to normotensive individuals. On the other hand, some prospective data suggest that a history of nephrolithiasis was associated with a greater tendency to develop hypertension. Newer epidemiologic data also link obesity and diabetes, features of the metabolic syndrome, with nephrolithiasis. In this review, the association of hypertension, diabetes, and obesity with nephrolithiasis is reviewed, and possible pathogenic mechanisms are discussed. Patients with hypertension may have abnormalities of renal calcium metabolism, but data confirming this hypothesis are inconsistent. Higher body mass index and insulin resistance (i.e., the metabolic syndrome) may be etiologic in uric acid nephrolithiasis as increasing body weight is associated with decreasing urinary pH. The possibility that common pathophysiologic mechanisms underly these diseases is intriguing, and if better understood, could potentially lead to better therapies for stone prevention. Both hypertension and stones might be addressed through lifestyle modification to prevent weight gain. Adoption of a lower sodium diet with increased fruits and vegetables and low-fat dairy products, (for example, the dietary approaches to stop hypertension(DASH) diet), may be useful to prevent both stones and hypertension. In those patients in whom dietary modification and weight loss are ineffective, thiazide diuretics are likely to improve blood pressure control and decrease calciuria.

Molecular variants of the thiazide-sensitive Na+-Cl- cotransporter in hypertensive families

BACKGROUND

The thiazide-sensitive Na-Cl cotransporter (TSC) is involved in the fine regulation of sodium excretion by the kidney, and an increase in its activity causes salt-sensitive hypertension and hypercalciuria.

METHODS

To explore the possibility that activating mutations in the TSC gene may be involved in the pathogenesis of primary hypertension, we screened genomic DNA of 68 individuals from hypertensive families of patients with hypercalciuria for variations using single-strand conformation polymorphism and investigated the functional properties using the Xenopus laevis oocyte expression system.

RESULTS

We identified 18 variants in the TSC and, of those, four were nonsynonymous. The A728T, R904Q and R919C variants were introduced into the human TSC cDNA and expressed in Xenopus oocytes to study their effect on Na transport. Although T728 and Q904 did not show any difference in Na uptake, the R919C mutant showed a 60% increase compared to wild-type human TSC and an exaggerated inhibitory action of hydrochlorothiazide. Immunocytochemical analysis revealed no difference in cell surface expression of R919C mutants compared to wild-type hTSC. There was no significant difference in the inhibitory effect of the carboxyl terminus of the serine-threonine kinase WNK4 on the R919C mutant and wild-type hTSC.

CONCLUSIONS

Our results show that the substitution of arginine for cysteine at position 919 of TSC increases Na transport function, and provide support for the hypothesis that mutations in renal tubular sodium transporters may contribute to the development of primary hypertension, a polygenic disorder, by increasing renal sodium reabsorption.

Ethnic differences in relative risk of idiopathic calcium nephrolithiasis in North America

PURPOSE

Data on susceptibility to kidney stone disease are sparse in individuals of nonEuropean ancestry residing in North America. We determined the relative risk of calcium nephrolithiasis among people of different ethnic backgrounds living in the same geographic region.

MATERIALS AND METHODS

Using a cross-sectional design 1,128 consecutive patients with idiopathic calcium nephrolithiasis 18 to 50 years old were recruited from a population based Kidney Stone Center in Toronto. Age and gender adjusted odds ratios and 95% confidence intervals were calculated by logistic regression using the 2001 Canada Census population data.

RESULTS

Compared to Europeans the relative risk of calcium nephrolithiasis was significantly higher in individuals of Arabic (OR 3.8, 2.7-5.2), West Indian (OR 2.5, 1.8-3.4), West Asian (OR 2.4, 1.7-3.4) and Latin American (OR 1.7, 1.2-2.4) origin, and significantly lower in those of East Asian (OR 0.4, 0.3-0.5) and African (OR 0.7, 0.5-0.9) background. Several ethnic groups had kidney stone risk factors that were significantly different from those of the European group including higher urinary uric acid, urea excretion and estimated protein intake, and lower urinary citrate, potassium, magnesium and phosphate excretion. However, none was consistent with the variation in relative risk of stone disease overall.

CONCLUSIONS

The propensity for the development of calcium nephrolithiasis differed markedly among ethnic groups in North America. While environmental factors could not be completely ruled out, this variability may reflect the influence of genetic susceptibility because there was no dominant environmental factor to account for the differences in relative risk of stone disease.