Idiopathic hypercalciuria

Beta-thalassaemia major: Prevalence, risk factors and clinical consequences of hypercalciuria

Regular transfusion and chelation therapy produces increased life expectancy in thalassaemic patients who may develop new complications. Since few data are available regarding hypercalciuria in β‐thalassaemia major (TM), the aim of our study was to evaluate its prevalence, risk factors and clinical consequences. We enrolled 176 adult TM patients followed at the Center of Thalassemia of Ferrara. Hypercalciuria was defined by a calciuria of 4 mg/kg/day or more in a 24‐h urine sample. Anamnestic, biochemical and radiological data were collected. Hypercalciuria prevalence was reported in 69.3% of patients (females 52.5%). Hypercalciuric (HC) patients used deferasirox (DFX) more often than normocalciuric (NC) patients (47.5% vs 29.6%; p < 0.05). In HC subjects plasma parathyroid hormone (PTH) (24.1 ± 10.4 vs 30.1 ± 13.2 pg/ml) and phosphate levels (3.6 ± 0.5 vs 3.8 ± 0.7 mg/dl) were lower, whereas serum calcium (9.6 ± 0.4 vs 9.4 ± 0.4 mg/dl) and urinary 24‐h phosphaturia (0.9 ± 0.4 vs 0.6 ± 0.3 g/day) were higher as compared to NC patients (p < 0.05 for all comparisons). Supplementation with oral calcium and cholecalciferol was similar between the groups. A higher rate of kidney stones was present in HC (14.8%) versus NC patients (3.7%) (p < 0.05). Hypercalciuria is a frequent complication in adequately treated adult TM patients. Hypercalciuria prevalence is increased in DFX users whereas haemoglobin level or calcium supplements play no role. A significant proportion of HC patients developed kidney stones.

Mutations in CLDN2 Are Not a Common Cause of Pediatric Idiopathic Hypercalciuria in Canada

Background:

Hypercalciuria is the most common risk factor for kidney stone formation, including in pediatric patients. However, the etiology is often unknown and children are frequently diagnosed with idiopathic hypercalciuria. Nearly 50% of children with hypercalciuria have a first-degree relative with kidney stones, suggesting a strong genetic basis for this disease. A failure of calcium reabsorption from the proximal nephron is implicated in the pathogenesis of hypercalciuria. Claudin-2 is a tight junction protein abundantly expressed in the proximal tubule. It confers paracellular permeability to calcium that is essential for transport across the proximal tubule where the majority of filtered calcium is reabsorbed.

Objective:

Our objective was to examine the frequency of coding variations in CLDN2 in a cohort of children with idiopathic hypercalciuria.

Design:

Mixed method including retrospective chart review and patient interview, followed by genetic sequencing.

Setting:

Three tertiary care centers in Canada.

Patients:

Children (age 1-18 years) with idiopathic hypercalciuria. Patients with other causes of hypercalciuria were excluded.

Methods:

Data were collected from 40 patients with idiopathic hypercalciuria. Informed consent to collect DNA was obtained from 13 patients, and the final and only coding exon of CLDN2 was sequenced.

Results:

The majority of patients were male, white, and had a positive family history of kidney stones. Parathyroid hormone levels were significantly lower than the reference range (P < .001). The levels of 1,25-dihydroxyvitamin D were also significantly higher in our patient cohort, relative to the reference range (P < .001). Sequence analysis of CLDN2 did not identify any coding variations.

Limitations:

Sequencing analysis was limited to the final coding exon and small sample size.

Conclusions:

CLDN2 coding variations are not a common cause of idiopathic hypercalciuria in Canadian children. Further study is needed to determine the causes of hypercalciuria in pediatric patients and develop targeted therapies.

Medical evaluation and pharmacotherapeutical strategies in management of urolithiasis

Treatment of urolithiasis depends on several important factors which include stone location, size, composition, and patient symptoms. Although significant advancements have been made in the surgical management of urolithiasis in the last decade, pharmacotherapy which can prevent the formation of new stones and decrease the recurrence of urolithiasis has not experienced the same level of success. Currently, urolithiasis is regarded as a complicated syndrome that is determined by numerous factors, and any treatment plan for urolithiasis should be individualized while considering any potential damage arising from stone-forming factors. This review introduces the most popular methods currently used to evaluate urolithiasis and the pharmacotherapy of urolithiasis based on patient-specific factors.

Association between single nucleotide polymorphism (rs4252424) in TRPV5 calcium channel gene and lead poisoning in Chinese workers

Background

Lead (Pb) is broadly used in various industries and causes irreversible damage to human tissues, organs, and systems. Studies have revealed that lead exerts toxic effects via interfering with calcium channel.

Methods

In the present study, we investigated whether single nucleotide polymorphisms (SNPs) in TRPV5, a calcium channel‐related gene, were associated with lead exposure susceptibility. By using TaqMan SNP genotyping, we performed genotyping of eight TRPV5 tag‐SNPs in 1,130 lead‐exposed Chinese workers with similar lead exposure level.

Results

Single nucleotide polymorphism rs4252424 was significantly associated with lead susceptibility, measured by blood lead level (BLL) (β = −0.069, p_linear = 0.029). However, there was no significant association between any other seven SNPs and BLL. The further expression Quantitative Trait Loci displayed that CC genotype of rs4252424 is significant associated with higher BLL than CT (p < 0.0001).

Conclusion

We conclude that SNP rs4252424 has the potential to evaluate lead susceptibility in the Chinese occupational population, and further enhance lead exposure prevention and intervention.

Association of urinary calcium excretion with serum calcium and vitamin D levels

BACKGROUND AND OBJECTIVES

Population-based data on urinary calcium excretion are scarce. The association of serum calcium and circulating levels of vitamin D [25(OH)D2 or D3] with urinary calcium excretion in men and women from a population-based study was explored.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

Multivariable linear regression was used to explore factors associated with square root-transformed 24-hour urinary calcium excretion (milligrams per 24 hours) taken as the dependent variable with a focus on month-specific vitamin D tertiles and serum calcium in the Swiss Survey on Salt Study.

RESULTS

In total, 624 men and 669 women were studied with mean ages of 49.2 and 47.0 years, respectively (age range=15-95 years). Mean urinary calcium excretion was higher in men than in women (183.05 versus 144.60 mg/24 h; P<0.001). In adjusted models, the association (95% confidence interval) of square root urinary calcium excretion with protein-corrected serum calcium was 1.78 (95% confidence interval, 1.21 to 2.34) mg/24 h per milligram per deciliter in women and 0.59 (95% confidence interval, -0.11 to 1.29) mg/24 h per milligram per deciliter in men. Men in the third 25(OH)D3 tertile had higher square root urinary calcium excretion than men in the first tertile (0.99; 95% confidence interval, 0.36 to 1.63 mg/24 h per nanogram per milliliter), and the corresponding association was 0.32 (95% confidence interval, -0.22 to 0.85) mg/24 h per nanogram per milliliter in women. These sex differences were more marked under conditions of high urinary sodium or urea excretions.

CONCLUSIONS

There was a positive association of serum calcium with urinary calcium excretion in women but not men. Vitamin 25(OH)D3 was associated with urinary calcium excretion in men but not women. These results suggest important sex differences in the hormonal and dietary control of urinary calcium excretion.

Therapy of hypoparathyroidism by replacement with parathyroid hormone

Hypoparathyroidism (HypoPT) is a state of hypocalcemia due to inappropriate low levels of parathyroid hormone (PTH). HypoPT is normally treated by calcium supplements and activated vitamin D analogues. Although plasma calcium is normalized in response to conventional therapy, quality of life (QoL) seems impaired and patients are at increased risk of renal complications. A number of studies have suggested subcutaneous injections with PTH as an alternative therapy. By replacement with the missing hormone, urinary calcium may be lowered and QoL may improve. PTH replacement therapy (PTH-RT) possesses, nevertheless, a number of challenges. If PTH is injected only once a day, fluctuations in calcium levels may occur resulting in hypercalcemia in the hours following an injection. Twice-a-day injections seem to cause less fluctuation in plasma calcium but do stimulate bone turnover to above normal. Most recently, continuous delivery of PTH by pump has appeared as a feasible alternative to injections. Plasma calcium levels do not fluctuate, urinary calcium is lowered, and bone turnover is only stimulated modestly (into the normal range). Further studies are needed to assess the long-term effects. If beneficial, it seems likely that standard treatment of HypoPT in the future will change into replacement therapy with the missing hormone.

The role of claudin in hypercalciuric nephrolithiasis

Calcium nephrolithiasis is a common condition. Family-based genetic linkage studies and genome-wide association studies (GWASs) have uncovered a run of important candidate genes involved in renal Ca(++) disorders and kidney stone diseases. The susceptible genes include NKCC2, ROMK and ClCkb/Barttin that underlie renal salt excretion; claudin-14, -16 and -19 that underlie renal Ca(++) excretion; and CaSR that provides a sensing mechanism for the kidney to regulate salt, water and Ca(++) homeostasis. Biological and physiological analyses have revealed the cellular mechanism for transepithelial Ca(++) transport in the kidney that depends on the concerted action of these gene products. Although the individual pathogenic weight of the susceptible genes in nephrolithiasis remains unclear, perturbation of their expression or function compromises the different steps within the integrated pathway for Ca(++) reabsorption, providing a physiological basis for diagnosing and managing kidney stone diseases.

Loss-of-function mutations of CYP24A1, the vitamin D 24-hydroxylase gene, cause long-standing hypercalciuric nephrolithiasis and nephrocalcinosis

PURPOSE

Hypercalciuria is the most common cause of kidney stone disease and genetic factors have an important role in nearly half of these cases. Recently loss-of-function mutations of CYP24A1, the gene encoding vitamin D 24-hydroxylase, were identified in idiopathic infantile hypercalcemia. We describe the clinical and molecular basis of severe long-standing kidney stone disease in adults caused by CYP24A1 mutations.

MATERIALS AND METHODS

Three subjects from 2 Israeli families with nephrolithiasis and nephrocalcinosis were clinically characterized. Genomic DNA was isolated from peripheral blood and sequencing of CYP24A1 was performed.

RESULTS

All subjects presented with severe kidney stone disease, the cause of which was not discovered for decades despite extensive evaluation. They all had hypercalciuria, nephrocalcinosis and intermittent hypercalcemia, and chronic kidney insufficiency developed in the oldest subject. All patients had a typical pattern of test results, including normal-high serum calcium, low parathyroid hormone levels, high vitamin D 25-(OH)D3 and 1,25-(OH)2D3, and low 24,25-(OH)2D3. Overall 3 CYP24A1 loss-of-function mutations were identified, including a homozygous deletion (delE143) in consanguinous family 1, and compound heterozygous mutations L409S and the novel W268-stop in family 2.

CONCLUSIONS

Loss-of-function mutations of CYP24A1 gene, encoding for 1,25-dihydroxyvitamin D3 24-hydroxylase, cause severe hypercalciuric nephrolithiasis and nephrocalcinosis. The mutations may present in adults and may lead to chronic renal insufficiency. Our results support a recessive mode of inheritance. CYP24A1 mutations should be considered in the differential diagnosis of hypercalciuric nephrolithiasis, especially as many adults are now prescribed supplemental oral vitamin D.

Bisphosphonates in the management of idiopathic hypercalciuria associated with osteoporosis: a new trick from an old drug

Idiopathic hypercalciuria (IHC) is defined as a 24-hour urinary calcium excretion that exceeds 4 mg/kg/day, regardless of gender and in absence of systemic diseases or pharmacological treatments that may cause normocalcemic hypercalciuria (eg sarcoidosis, normocalcemic primary hyperparathyroidism, vitamin D intoxication, hyperthyroidism). Patients with IHC and nephrolithiasis often present increased bone turnover, decreased bone mineral density (BMD) and increased susceptibility to fragility fractures. Although the pathogenesis of IHC seems complex and multifactorial, recent evidences suggest that cells involved in bone resorption may play a critical role in the chain of events leading to the excessive urinary calcium excretion. Therefore, it has been proposed that bisphosphonates, potent inhibitors of bone resorption, may have beneficial effects in hypercalciuric patients with low BMD. This manuscript reports recent findings regarding the role of bone tissue in the pathogenesis of IHC, and supports the use of bisphosphonates in such conditions. It also reviews the literature on the effects of bisphosphonates in subjects with osteoporosis-associated IHC.

Vitamin D, calcium, and cardiovascular mortality: a perspective from a plenary lecture given at the annual meeting of the American Association of Clinical Endocrinologists

OBJECTIVE

To examine data showing associations between serum 25-hydroxyvitamin D levels and calcium intake and cardiovascular mortality.

METHODS

The articles reviewed include those published from 1992-2011 derived from search engines (PubMed, Scopus, Medscape) using the following search terms: vitamin D, calcium, cardiovascular events, cardiovascular mortality, all-cause mortality, vascular calcification, chronic kidney disease, renal stones, and hypercalciuria. Because these articles were not weighted (graded) on the level of evidence, this review reflects my own perspective on the data and how they should be applied to clinical management.

RESULTS

For skeletal health, vitamin D and calcium are both needed to ensure proper skeletal growth (modeling) and repair (remodeling). Nutritional deficiencies of either vitamin D or calcium may lead to a spectrum of metabolic bone disorders. Excessive consumption of either nutrient has been linked to a variety of medical disorders, such as hypercalcemia or renal stones. There have also been associations between vitamin D or calcium intake and cardiovascular disease. However, neither of these associations have established evidence nor known causality for increasing cardiovascular risk or all-cause mortality in patients with creatinine clearances greater than 60 mL/min. In patients with more severe chronic kidney disease, stronger data link excess calcium (or phosphorus) intake and increase in vascular calcification, but not mortality. The safe upper limit for vitamin D intake is at least 4000 IU daily and probably 10 000 IU daily; for calcium, the safe upper limit is between 2000 and 3000 mg daily.

CONCLUSIONS

While no solid scientific evidence validates that serum vitamin D levels between 15 and 70 ng/mL are associated with increased cardiovascular disease risk, stronger but inconsistent evidence shows an association between calcium supplementation greater than 500 mg daily and an increase in cardiovascular disease risk. Most professional societies suggest that replacement levels of these nutrients be personalized with the goal of reaching a 25-hydroxyvitamin D concentration between 30 and 50 ng/mL and a calcium intake of 1200 mg daily.

Prevalence and factors associated with idiopathic hypercalciuria in HIV patients on combination antiretroviral therapy

Idiopathic hypercalciuria may lead to bone loss via three pathogenic mechanisms described in HIV-negative patients: intestinal hyperabsorption, kidney loss and bone hyperabsorption. We conducted a cross-sectional study in a cohort of 217 HIV-positive antiretroviral-experienced patients, identifying hypercalciuria in 67 patients: the prevalence was 30.9% (95% confidence interval 27.4-37.0). The occurrence of hypercalciuria in subjects with normal values of parathormone may indicate an absorptive form of hypercalciuria. In this sample, other bone turnover markers and T-scores were not related to the condition. The results of this study show a high prevalence of idiopathic hypercalciuria in a group of antiretroviral-experienced patients. The consequences and the exact causes of this metabolic complication are not yet known and further investigation is needed.

Progressive renal papillary calcification and ureteral stone formation in mice deficient for Tamm-Horsfall protein

Mammalian urine contains a range of macromolecule proteins that play critical roles in renal stone formation, among which Tamm-Horsfall protein (THP) is by far the most abundant. While THP is a potent inhibitor of crystal aggregation in vitro and its ablation in vivo predisposes one of the two existing mouse models to spontaneous intrarenal calcium crystallization, key controversies remain regarding the role of THP in nephrolithiasis. By carrying out a long-range follow-up of more than 250 THP-null mice and their wild-type controls, we demonstrate here that renal calcification is a highly consistent phenotype of the THP-null mice that is age and partially gene dosage dependent, but is gender and genetic background independent. Renal calcification in THP-null mice is progressive, and by 15 mo over 85% of all the THP-null mice develop spontaneous intrarenal crystals. The crystals consist primarily of calcium phosphate in the form of hydroxyapatite, are located more frequently in the interstitial space of the renal papillae than intratubularly, particularly in older animals, and lack accompanying inflammatory cell infiltration. The interstitial deposits of hydroxyapatite observed in THP-null mice bear strong resemblances to the renal crystals found in human kidneys bearing idiopathic calcium oxalate stones. Compared with 24-h urine from the wild-type mice, that of THP-null mice is supersaturated with brushite (calcium phosphate), a stone precursor, and has reduced urinary excretion of citrate, a stone inhibitor. While less frequent than renal calcinosis, renal pelvic and ureteral stones and hydronephrosis occur in the aged THP-null mice. These results provide direct in vivo evidence indicating that normal THP plays an important role in defending the urinary system against calcification and suggest that reduced expression and/or decreased function of THP could contribute to nephrolithiasis.

Evaluation of calcium excretion in Brazilian infantile and young population environmentally exposed to lead

Lead exposure is an important issue in the research of several toxic effects resulting from the biochemical interaction between this metal and the organism. Calcium is a fundamental mineral for the maintenance of the organism homeostasis where there is interaction between lead and calcium in metabolic pathways. Environmental lead exposure by verifying the usefulness and applicability of urinary calcium/creatinine ratio (UCa/Cr) in this context was evaluated. This was an extensive socio-demographic study of the nutritional profile, lead exposure biomarkers in blood and the urine and UCa/Cr ratio. The children studied were from a low socio-economic group characterized by unsatisfactory nutritional diet. Lead environmental exposure was shown by biomarkers, with UCa/Cr ratio having positive and significant correlations with both lead and delta-aminolevulinic acid in urine (ALA-U), without colinearity diagnosis. There was a strong association between calcium excretion and lead exposure as a result of linear regression construction models. In children, lead increases calcium excretion which is an additional risk to infantile health. Urinary calcium/creatinine ratio may be a useful tool in the biological monitoring of lead exposure and health promotion programs.

Alendronate and indapamide alone or in combination in the management of hypercalciuria associated with osteoporosis: a randomized controlled trial of two drugs and three treatments

BACKGROUND

The role of bisphosphonates (BPs) in the management of patients with hypercalciuria (HC) associated with osteoporosis is still uncertain. The aim of the study was to evaluate the effect of alendronate and indapamide alone or in combination on bone mineral density (BMD) and 24-h urinary calcium excretion (24-CaU) in post-menopausal women with HC and low BMD.

METHODS

A total of 77 post-menopausal women with HC (24-CaU > 4 mg/kg/day) and low BMD [T-score < -2.0 at lumbar spine (LS), femoral neck (FN) or total hip (TH)] from two centres of Northern Italy were randomized to receive indapamide 2.5 mg daily alone (24 patients, IND group), alendronate 70 mg weekly alone (27 patients, ALN group) or the combination therapy (26 patients, ALN + IND group). Throughout the study, all subjects received daily calcium supplements, depending on their dietary intake, to maintain a daily input of 1000 mg. Patients were instructed to increase water intake up to 2000 mL daily. The percentage and absolute changes of BMD at LS, FN and TH, and the variation of 24-CaU from baseline at 1 year were the primary outcomes. Serum calcium, phosphate, parathyroid hormone and bone alkaline phosphatase were also measured.

RESULTS

Overall 67 women completed the study and were included in the final analysis. Patients in the three groups were similar with regard to baseline characteristics. BMD did not significantly change from baseline after 1 year of treatment with indapamide (LS: +1 +/- 3.1%; FN: -0.3 +/- 3.5%; TH: -0.4 +/- 3.1%), while it showed a significant increase from baseline in the other two groups (ALN; LS: +5.8 +/- 4.2%, P < 0.001; FN: +3.9 +/- 7.9%, P = 0.018; TH: +2 +/- 3.6%, P = 0.006) (ALN + IND; LS: +8.2 +/- 5.3%, P < 0.001; FN: +4.9 +/- 6.7%, P = 0.007; TH: +2.9 +/- 4.2%, P = 0.004). Patients in the combination group showed a significantly higher increase of BMD at LS compared to ALN (P = 0.04). After 1 year, 24-CaU values significantly decreased from baseline in all groups (IND, 239 +/- 78 versus 364 +/- 44, P < 0.001) (ALN, 279 +/- 68 versus 379 +/- 79, P < 0.001) (ALN + IND, 191 +/- 68 versus 390 +/- 55, P < 0.001). The mean percentage decrease of 24-CaU in ALN + IND group (-50%) was significantly greater compared to ALN (-24%, P < 0.001) and IND (-35%, P = 0.012).

CONCLUSIONS

These results show a benefit, in terms of BMD improvement and 24-CaU reduction, associated with BPs' therapy in combination with indapamide in HC associated with osteoporosis. The combination therapy demonstrated a reduction of 24-CaU and an increase in LS BMD superior to that observed with alendronate alone. Our results support a new potential approach with BPs associated with thiazide diuretics or indapamide in the management of post-menopausal women with HC and associated bone loss. Studies on the larger sample size are needed to demonstrate the efficacy on the fracture outcome.

Evaluation of patients with a recent clinical fracture and osteoporosis, a multidisciplinary approach

The aetiology of osteoporotic fractures is multifactorial, but little is known about the way to evaluate patients with a recent clinical fracture for the presence of secondary osteoporosis.

The purpose of this study was to determine the prevalence of contributors to secondary osteoporosis in patients presenting with a clinical vertebral or non-vertebral fracture. Identifying and correcting these contributors will enhance treatment effect aimed at reducing the risk of subsequent fractures.

In a multidisciplinary approach, including evaluation of bone and fall-related risk factors, 100 consecutive women (n = 73) and men (n = 27) older than 50 years presenting with a clinical vertebral or non-vertebral fracture and having osteoporosis (T-score ≤-2.5) were further evaluated clinically and by laboratory testing for the presence of contributors to secondary osteoporosis.

In 27 patients, 34 contributors were previously known, in 50 patients 52 new contributors were diagnosed (mainly vitamin D deficiency in 42) and 14 needed further exploration because of laboratory abnormalities (mainly abnormal thyroid stimulating hormone in 9). The 57 patients with contributors were older (71 vs. 64 yrs, p < 0.01), had more vertebral deformities (67% vs. 44%, p < 0.05) and a higher calculated absolute 10-year risk for major (16.5 vs. 9.9%, p < 0.01) and for hip fracture (6.9 vs. 2.4%, p < 0.01) than patients without contributors. The presence of contributors was similar between women and men and between patients with fractures associated with a low or high-energy trauma.

We conclude that more than one in two patients presenting with a clinical vertebral or non-vertebral fracture and BMD-osteoporosis have secondary contributors to osteoporosis, most of which were correctable. Identifying and correcting these associated disorders will enhance treatment effect aimed at reducing the risk of subsequent fractures in patients older than 50 years.

Recent advances in renal tubular calcium reabsorption

PURPOSE OF REVIEW

Knowledge of renal Ca2+ reabsorption has evolved greatly in recent years. This review focuses on two recent discoveries concerning passive and active Ca2+ reabsorption.

RECENT FINDINGS

The thiazide diuretics are known for their hypocalciuric effect. Recently, it has been demonstrated that TRPV5-knockout mice, in which active Ca2+ reabsorption in the distal convoluted tubule is completely abolished, show the same sensitivity towards thiazides as wild-type mice. This indicates that thiazide affects Ca2+ reabsorption indirectly via contraction of the extracellular volume, independent of active Ca2+ reabsorption in the distal convoluted tubule, thereby increasing passive paracellular Ca2+ transport in the proximal tubule. Moreover, the antiaging hormone Klotho regulates Ca2+ reabsorption in the distal convoluted tubule via a novel molecular mechanism. Klotho stabilizes the TRPV5 Ca2+ channel in the plasma membrane by deglycosylation of the protein.

SUMMARY

By showing that thiazide-induced hypercalciuria is due to increased passive Ca2+ reabsorption in the proximal tubule, a long-standing issue has been solved, underlining the importance of proximal paracellular Ca2+ reabsorption. Moreover, the molecular mechanism by which the antiaging hormone Klotho regulates TRPV5 activity may prove to be generally applicable in Klotho-mediated prevention of aging.