Urinary calcium excretion in healthy children and children with primary monosymptomatic nocturnal enuresis

Differences in the urinary metabolome and proteome between wet and dry nights in children with monosymptomatic nocturnal enuresis and nocturnal polyuria

BACKGROUND

Nocturnal enuresis (NE) is a common disease with multiple pathogenic mechanisms. This study aimed to compare levels of metabolites and proteins between wet and dry nights in urine samples from children with monosymptomatic NE (MNE).

METHODS

Ten boys with MNE and nocturnal polyuria (age: 7.6 ± 1.3 years) collected their total nighttime urine production during a wet and a dry night. Untargeted metabolomics and proteomics were performed on the urine samples by liquid chromatography coupled with high-mass accuracy tandem mass spectrometry (LC-MS/MS).

RESULTS

On wet nights, we found reduced urine osmolality (P = 0.025) and increased excretion of urinary potassium and sodium by a factor of, respectively, 2.1 (P = 0.038) and 1.9 (P = 0.19) compared with dry nights. LC-MS identified 59 metabolites and 84 proteins with significantly different levels between wet and dry nights (fold change (FC) < 0.67 or > 1.5, P < 0.05). Some compounds were validated by different methodologies. During wet nights, levels of compounds related to oxidative stress and blood pressure, including adrenalin, were increased. We found reduced levels of aquaporin-2 on wet nights. The FCs in the 59 metabolites were positively correlated to the FCs in the same metabolites identified in urine samples obtained during the evening preceding wet and dry nights.

CONCLUSIONS

Oxidative stress, which in the literature has been associated with nocturia and disturbances in sleep, might be increased during wet nights in children with MNE. We further found evidence of increased sympathetic activity. The mechanisms related to having wet nights in children with MNE seem complex, and both free water and solute handling appear to be important. A higher resolution version of the Graphical abstract is available as Supplementary information.

Calciuria in children with primary mono-symptomatic nocturnal enuresis

Introduction: The prevalence of idiopathic hypercalciuria (IH) in healthy pediatric population ranges from 3.0% to 7.0%. There is insufficient data about IH in children with mono-symptomatic enuresis. The aim of this study was to examine calcium excretion in urine (UCa) in patients with primary mono-symptomatic nocturnal enuresis (PMNE). Methods: In patients with PMNE, aged 5 to 17 years, IH was determined in 24-h urine and from second morning spot urine. The completeness of the 24-h urine collections was estimated via measuring 24h-urine creatinine excretion (UCr) of 0.1-0.2 mmol/kg/24h. Results: Sixty patients with PMNE, 32 males and 28 girls, median age of 9 years were enrolled in the study. Only 41.7% patients successfully completed 24 h urine collection. IH, defined as 24-h UCa > 0.1 mmol/kg body weight, was diagnosed in 12% of the patients, while when defined as UCa/UCr > 0.8 mmol/mmol in children 5-7 years and > 0.6 mmol/mmol in those > 7 years, IH was 8.3% and 6.7% from 24hurine and spot urine, respectively. Conclusion: Children and adolescents with PMNE are in risk of hypercalciuria. Therefore, it is useful to examine 24 hours of urine calcium excretion in these patients.

Hypercalciuria in children with monosymptomatic nocturnal enuresis

OBJECTIVE

The aim of this study was to measure the 24 h urinary calcium content in children with monosymptomatic nocturnal enuresis (MNE) and compare with those in healthy children to investigate whether there is any relation with enuresis and hypercalciuria.

MATERIAL AND METHODS

This study included 120 children and adolescents with MNE aged between 7 and 14 years. Eighty age- and sex-matched healthy children served as a control group. To determine urinary calcium excretion, 24 h urine samples were collected. The children with enuresis were divided into two sub-groups as hypercalciuric and normocalciuric groups according to the amount of urinary calcium excretion.

RESULTS

Hypercalciuria was found in 27 (23%) of the MNE patients compared with two (4%) of continent children (p<0.001). In addition, the mean 24 h urine calcium/body weight ratio was higher in the enuresis group than in the control group, 2.94±2.42 versus 1.59±1.72, respectively (p=0.002). When the children with enuresis were divided into two groups as normokalsiuric and hypercalciuric, the hypercalciuric children were younger and the majority of this group were boys..

CONCLUSIONS

Our study showed that hypercalciuria is common in children with MNE, so we suggested measuring urine calcium levels in NE patients. However, further studies are needed to clarify the relationship between hypercalciuria and NE in larger series..

Urinary calcium excretion in children with monosymptomatic enuresis

Background

Among many factors predisposing to monosymptomatic enuresis (MNE) disturbances in urinary electrolites excretion play an important role. Because of many controversies in this field there is a need to debate the role of hypercalciuria in MNE. The aim of our study was to determine the urinary calcium in children with MNE.

Methods

The investigation was conducted on 204 children (83 MNE children and 121 reference group). Urinary calcium excretion (in 24-h collection and per kg of body mass), Ca/creatinine ratio, Ca²⁺ in urine sample and in 24-h collection of urine were estimated.

Results

Hypercalciuria in MNE group was diagnosed in 18/83 (21.69 %) patients. We found statistically significant differences between children with MNE in Ca²⁺ in urine sample and 24-h collection and Ca/creat. ratio. Median urinary calcium excretion (mg/kg/24-h and mmol/24-h) was significantly higher in hypercalciuric enuretic patients. The urinary total calcium (mmol/24-h), urinary bound calcium and urinary calcium concentration (mmol/L) demonstrated a significant positive correlation with height, weight and age in reference group but not in MNE group.

Conclusion

Urinary calcium excretion was significantly disturbed and further studies are needed to assess the role of hypercalciuria in the pathogenesis of MNE.

Effects of Sex on Intra-Individual Variance in Urinary Solutes in Stone-Formers Collected from a Single Clinical Laboratory

Background/Aims

Our work in a rodent model of urinary calcium suggests genetic and gender effects on increased residual variability in urine chemistries. Based on these findings, we hypothesized that sex would similarly be associated with residual variation in human urine solutes. Sex-related effects on residuals might affect the establishment of physiological baselines and error in medical assays.

Methods

We tested the effects of sex on residual variation in urine chemistry by estimating coefficients of variation (CV) for urinary solutes in paired sequential 24-h urines (≤72 hour interval) in 6,758 females and 9,024 males aged 16–80 submitted to a clinical laboratory.

Results

Females had higher CVs than males for urinary phosphorus overall at the False Discovery Rate (P<0.01). There was no effect of sex on CV for calcium (P>0.3). Males had higher CVs for citrate (P<0.01) from ages 16–45 and females higher CVs for citrate (P<0.01) from ages 56–80, suggesting effects of an extant oestral cycle on residual variance.

Conclusions

Our findings indicate the effects of sex on residual variance of the excretion of urinary solutes including phosphorus and citrate; differences in CV by sex might reflect dietary lability, differences in the fidelity of reporting or genetic differentiation in renal solute consistency. Such an effect could complicate medical analysis by the addition of random error to phenotypic assays. Renal analysis might require explicit incorporation of heterogeneity among factorial effects, and for sex in particular.

Weight, age and coefficients of variation in renal solute excretion

BACKGROUND

Homoscedasticity (constant variance over axes or among statistical factors) is an integral assumption of most statistical analyses. However, a number of empirical studies in model organisms and humans demonstrate significant differences in residual variance (that component of phenotype unexplained by known factors) or intra-individual variation among genotypes. Our work suggests that renal traits may be particularly susceptible to randomization by genetic and non-genetic factors, including endogenous variables like age and weight.

METHODS

We tested associations between age, weight and intra-individual variation in urinary calcium, citrate, chloride, creatinine, potassium, magnesium, sodium, ammonium, oxalate, phosphorus, sulfate, uric acid and urea nitrogen in 9,024 male and 6,758 female kidney stone patients. Coefficients of variation (CVs) were calculated for each individual for each solute from paired 24-hour urines. Analysis of CVs was corrected for inter-measurement collection variance in creatinine and urine volume. CVs for sodium and urea nitrogen were included to correct for dietary salt and protein.

RESULTS

Age was positively associated with individual CVs for calcium and negatively associated with CVs for potassium, ammonium and phosphorus (p(FDR) < 0.01). Weight was associated with CVs for creatinine, magnesium and uric acid, and negatively associated with CVs for calcium, potassium and oxalate (p(FDR) < 0.05).

CONCLUSION

Intra-individual variation changes over age and weight axes for numerous urinary solutes. Changing residual variance over age and weight could cause bias in the detection or estimation of genetic or environmental effects. New methodologies may need to account for such residual unpredictability, especially in diverse collections.

Is there any correlation between hypercalciuria and nocturnal enuresis?

Nocturnal enuresis is a common problem among children. Hypercalciuria has been proposed as an important etiology of bedwetting. We investigated the incidence of hypercalciuria among children with nocturnal enuresis and age- and sex-matched healthy controls. In this case–control study 118 children with nocturnal enuresis and 100 age-, sex-, and educational district-matched healthy controls were recruited. Urine samples were obtained from each subject twice: immediately after awakening and 2 hours later at school. Urinary calcium and creatinine levels were measured and the subjects with a urinary calcium/creatinine ratio more than 0.2 were considered as hypercalciuric. Serum Ca, P, Na, K, and PTH levels were measured for all hypercalciuric subjects. The mean urine calcium to creatinine ratio in the second urine sample was 0.070±0.06 mg/mg and 0.050±0.046, respectively in the case and control groups (P=0.008). There were 12/118 and 3/100 hypercalciuric subjects in the case and control groups respectively (P=0.032). The serum Ca, P, Na, K, and PTH levels were in normal range in all hypercalciuric subjects. In our study there was a significant difference in the frequency of hypercalciuria among children with nocturnal enuresis and healthy controls, so we can suggest adding the measurement of urine electrolytes especially the calcium level in patients with nocturnal enuresis.

Bone disease in pediatric idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) is the leading metabolic risk factor for urolithiasis and affects all age groups without gender or race predominance. IH has a high morbidity with or without lithiasis and reduced bone mineral density (BMD), as described previously in pediatric patients as well as in adults. The pathogenesis of IH is complex and not completely understood, given that urinary excretion of calcium is the end result of an interplay between three organs (gut, bone and kidney), which is further orchestrated by hormones, such as 1,25 dihydroxyvitamin D, parathyroid hormone, calcitonin and fosfatonins (i.e., fibroblast growth-factor-23). Usually, a primary defect in one organ induces compensatory mechanisms in the remaining two organs, such as increased absorption of calcium in the gut secondary to a primary renal loss. Thus, IH is a systemic abnormality of calcium homeostasis with changes in cellular transport of this ion in intestines, kidneys and bones. Reduced BMD has been demonstrated in pediatric patients diagnosed with IH. However, the precise mechanisms of bone loss or failure of adequate bone mass gain are still unknown. The largest accumulation of bone mass occurs during childhood and adolescence, peaking at the end of the second decade of life. This accumulation should occur without interference to achieve the peak of optimal bone mass. Any interference may be a risk factor for the reduction of bone mass with increased risk of fractures in adulthood. This review will address the pathogenesis of IH and its consequence in bone mass.

Relief of Nocturnal Enuresis by Desmopressin Is Kidney and Vasopressin Type 2 Receptor Independent

Primary nocturnal enuresis (PNE) is a common problem in childhood and adolescence. Although various treatments are highly effective, a common underlying hypothesis on the pathogenesis is lacking. The success of desmopressin, a synthetic analogue of the antidiuretic hormone vasopressin, has been attributed to increased renal water reabsorption that is mediated by activation of the renal vasopressin V2 receptor (V2R). However, this effect does not explain other symptoms of PNE, such as the failure to arouse upon bladder distension. This study identified a family in which one child displayed PNE and coexisting nephrogenic diabetes insipidus, as a result of a novel nonsense mutation in the V2R gene (C358X). Cell-biologic investigations revealed that V2R-C358X is retained in the endoplasmic reticulum and is unstable, which explains his nephrogenic diabetes insipidus. Consistently, extrarenal V2R-mediated responses were absent in the patient who was treated with desmopressin. Administration of desmopressin, however, changed his PNE into nocturia, because he now still voided unchanged high urinary volumes at night but woke up and went to the bathroom. Withdrawal of desmopressin was accompanied by bedwetting, whereas reintroduction again relieved the symptoms. Therefore, these data indicate that neither a functioning renal concentration system nor a functional V2R is needed for the therapeutic benefit of desmopressin in PNE. Rather, it suggests that another vasopressin receptor and other organ(s) is the target for desmopressin to relieve PNE.