Idiopathic hypercalciuria in children. Classification, clinical manifestations and outcome

Evolution of bone mineral density in patients with idiopathic hypercalciuria: a 20-year longitudinal study

BACKGROUND

Several recent studies reported bone mineral density (BMD) reduction in pediatric patients with idiopathic hypercalciuria (IH). This longitudinal study aimed to evaluate BMD evolution in IH patients through three bone densitometry studies conducted over 20 years on average. A second objective was to evaluate urine calcium and citrate excretion during this period.

METHODS

Case notes of 34 patients diagnosed with IH at age 7.9 ± 3, alongside results of two bone densitometry studies, performed at 10.5 ± 2.7 (BMD1) and 14.5 ± 2.7 (BMD2) years of age, were reviewed. Patients underwent a third densitometry study in adulthood (BMD3) aged 28.3 ± 2.9. Mean follow-up duration (time-lapse between BMD1 and BMD3) was 17.7 ± 1.4 years.

RESULTS

Statistically significant differences were found between z-BMD3 (- 0.85 ± 1.10) and z-BMD1 (- 1.47 ± 0.99) (P = 0.001) as well as between z-BMD3 and z-BMD2 (- 1.33 ± 1.20) (P = 0.016). At the end of follow-up, z-BMD3 was superior to z-BMD2 in 23 adult patients (67.6%) and lower in 11 patients (5M, 6F; 32.3%). Both men and women showed increased bone mass over time, although such increases were significant only for women. The gradual decrease observed in calcium/creatinine and citrate/creatinine ratios could be related to improvement in osteoblastic activity and especially reduction in osteoclastic activity.

CONCLUSIONS

In patients with IH, BMD improves, which may be related especially to female sex, increment of body mass, and reduction in bone resorption. Upon reaching adulthood, urine calcium and citrate excretion tend to decrease so lithogenic risk still remains. The cause of the latter is unknown, although it likely relates to changes in bone activity.

Longitudinal study of kidney water management in patients diagnosed with idiopathic hypercalciuria in childhood

INTRODUCTION

There is much debate about whether idiopathic hypercalciuria (IH) affects kidney water management. For the first time in the literature, we carried out a longitudinal study of kidney water management (KWM) in patients diagnosed with IH in childhood and followed-up until adulthood (mean follow-up 17.7±1.4 years).

METHODS

Twenty-nine patients (7 M, 22 F) over the age of 24 years (mean 28.2±2.9 years, range: 24.1-35.9) who were diagnosed with IH in childhood (mean 7.6±3.2 years, range: 1-14) were included. Maximum urine osmolality (UO) and/or urine volume adjusted for 100ml of glomerular filtration rate (V/GFR) in both age groups (paediatric and adult) were determined. Moreover, whenever possible, in both age groups plasma creatinine levels, plasma sodium levels, uric acid levels, the citrate/creatinine ratio and the calcium/citrate ratio were recorded and a renal and bladder ultrasound was performed.

RESULTS

In the paediatric age group, KWM was altered in 9/29 cases (31%) (4 with reduced maximum UO and 5 with elevated V/GFR). In adulthood, KWM was found to be affected in 7/29 cases (24.1%) (6 with reduced UO and one with elevated V/GFR). Compared to the paediatric age group, adult patients had lower V/GFR, calcium/creatinine and citrate/creatinine values, as well as higher plasma creatinine, uric acid and calcium/citrate. There were no differences in the maximum UO in both age groups. However, UO in adulthood was significantly lower in subjects who had renal colic compared to those who did not (P=.04).

CONCLUSIONS

KWM was affected in approximately one third of patients with IH, which persisted 20 years after diagnosis. We think that these results may be due to adherence to the recommended protective diet and to the pharmacological treatment administered at the diagnosis of IH during childhood.

The idiopathic hypercalciuria reviewed. Metabolic abnormality or disease?

Idiopathic hypercalciuria (IH) is defined as that clinical situation in which an increase in urinary calcium excretion is observed, in the absence of hypercalcemia and other known causes of hypercalciuria. In recent years, its diagnosis in pediatric age has been more frequent because it has been known that it can debut with very different symptoms, in the absence of kidney stone formation. The discovery of genetic hypercalciuric stone-forming rats has allowed us to glimpse the pathophysiological mechanism of IH since they show many data in common with humans with IH as normal levels of blood calcium, intestinal calcium hyperabsorption, increased bone resorption and a defect in the renal tubular calcium reabsorption. In 1993, it was shown that in these animals there is an increase in the number of vitamin D receptors (VDR) in the intestine, which favors an increase in the functional capacity of calcitriol-VDR complexes that explains the increase in intestinal transport of calcium. The same happens at the bone level producing a greater resorption. In our opinion, IH is a 'metabolic anomaly' or, better, an inheritable constitutive metabolic characteristic. In this sense, what patients with IH would inherit is the availability of having a greater number of VDRs in their cells than those with normal urinary calcium excretion. IH cannot be considered a sensu stricto disease, so pharmacological treatment must be individualized.

Hypercalcemic Disorders in Children

Hypercalcemia is defined as a serum calcium concentration that is greater than two standard deviations above the normal mean, which in children may vary with age and sex, reflecting changes in the normal physiology at each developmental stage. Hypercalcemic disorders in children may present with hypotonia, poor feeding, vomiting, constipation, abdominal pain, lethargy, polyuria, dehydration, failure to thrive, and seizures. In severe cases renal failure, pancreatitis and reduced consciousness may also occur and older children and adolescents may present with psychiatric symptoms. The causes of hypercalcemia in children can be classified as parathyroid hormone (PTH)-dependent or PTH-independent, and may be congenital or acquired. PTH-independent hypercalcemia, ie, hypercalcemia associated with a suppressed PTH, is commoner in children than PTH-dependent hypercalcemia. Acquired causes of PTH-independent hypercalcemia in children include hypervitaminosis; granulomatous disorders, and endocrinopathies. Congenital syndromes associated with PTH-independent hypercalcemia include idiopathic infantile hypercalcemia (IIH), William's syndrome, and inborn errors of metabolism. PTH-dependent hypercalcemia is usually caused by parathyroid tumors, which may give rise to primary hyperparathyroidism (PHPT) or tertiary hyperparathyroidism, which usually arises in association with chronic renal failure and in the treatment of hypophosphatemic rickets. Acquired causes of PTH-dependent hypercalcemia in neonates include maternal hypocalcemia and extracorporeal membrane oxygenation. PHPT usually occurs as an isolated nonsyndromic and nonhereditary endocrinopathy, but may also occur as a hereditary hypercalcemic disorder such as familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism, and familial isolated primary hyperparathyroidism, and less commonly, as part of inherited complex syndromic disorders such as multiple endocrine neoplasia (MEN). Advances in identifying the genetic causes have resulted in increased understanding of the underlying biological pathways and improvements in diagnosis. The management of symptomatic hypercalcemia includes interventions such as fluids, antiresorptive medications, and parathyroid surgery. This article presents a clinical, biochemical, and genetic approach to investigating the causes of pediatric hypercalcemia. © 2017 American Society for Bone and Mineral Research.

Estudo da excreção urinária de cálcio, potássio e sódio com o emprego de citrato de potássio na hipercalciúria idiopática na criança

OBJETIVO: Estudar as relações entre a excreção urinária de cálcio, sódio e potássio e a associação sódio/potássio urinários em crianças com hipercalciúria idiopática em dieta habitual, antes e depois da administração de citrato de potássio na dose de 1mEq/kg/dia. MÉTODOS: Foram estudadas prospectivamente 26 crianças: 19 (73%) meninos e sete (27%) meninas com idade entre dois e 13 anos, portadores de hipercalciúria idiopática recém-diagnosticada por dosagem de cálcio em urina de 24 horas >4mg/kg/dia. O citrato de potássio foi administrado na dose de 1mEq/kg/dia. Foram realizadas dosagens séricas e em urina de 24 horas de cálcio (Ca), potássio(K), sódio (Na) e creatinina (Cr), antes e 15 dias depois da administração diária do citrato de potássio. Para comparar os resultados de cálcio/creatinina (Ca/Cr), potássio/creatinina (K/Cr) e sódio/potássio (Na/K) urinários nos dois momentos, aplicou-se o teste não-paramétrico de Wilcoxon. Para a análise das associações entre Ca/Cr e K/Cr e entre Ca/Cr e Na/Cr foi utilizado o coeficiente de correlação de Pearson. Considerou-se significante p<0,05. RESULTADOS: Após o uso de citrato de potássio, ocorreu significativa redução da calciúria e da relação Na/K urinários, bem como elevação na caliúria. Não houve modificação da excreção urinária de sódio. CONCLUSÕES: Em dieta habitual, o citrato de potássio eleva a caliúria e diminui a calciúria em criança hipercalciúricas, sendo um eficaz recurso terapêutico.

[Study of renal morphology and function in children with nocturnal enuresis. Relationship with sensitivity or resistance to desmopressin]

BACKGROUND

In the last few years, there have been reports that children with nocturnal enuresis frequently have hypercalciuria. Likewise, children with desmopressin-resistant enuresis have recently been reported to have a higher renal concentration capacity than patients with desmopressin-sensitive enuresis.

OBJECTIVES

To study renal function and urinary calcium excretion and to register familial history of enuresis and urolithiasis in a group of children with enuresis, whether responders or nonresponders to desmopressin, followed-up in our hospital.

MATERIAL AND METHODS

A cohort of 60 patients (42 boys and 18 girls) who were referred to the hospital because of nocturnal enuresis.

RESULTS

Hypercalciuria was detected in 26 children (43.3 %) and hypocitraturia in eight (13.3 %). The frequency of hypercalciuria was higher in desmopressin-resistant patients than in desmopressin-sensitive patients, but this difference was not statistically significant. Sonographic renal morphological anomalies were detected in 11 children (18.3 %). No differences in renal handling of water were detected when the patients were distributed according to the grade of sensitivity to desmopressin.

CONCLUSIONS

In our cohort we found a high frequency of hypercalciuria in children with nocturnal enuresis. No differences were observed in maximal urinary osmolality among desmopressin-resistant and desmopressin-sensitive children.

Hypercalciuria and recurrent urinary tract infections: incidence and symptoms in children over 5 years of age

Hypercalciuria is an important and common risk factor in the formation of renal stones. In this study we evaluated the incidence and the clinical presentation of hypercalciuria in 75 children over 5 years of age with the diagnosis of recurrent urinary tract infection (UTI). We measured random urinary calcium/creatinine value (three times), 24-h urinary calcium excretion, serum calcium, phosphorus, electrolytes, blood gas, blood urea nitrogen and creatinine levels. Hypercalciuria was found in 32 patients (43%). The mean urinary calcium/creatinine ratio for hypercalciuric patients was 0.50+/-0.21 mg/mg (min: 0.24, max: 2.60). The mean urinary calcium/creatinine ratio for the rest of the study population--those without hypercalciuria--was 0.10+/-0.04 mg/mg (min: 0.01, max: 0.18). Presenting symptoms of the hypercalciuric patients and normocalciuric patients were similar. History of familial urolithiasis was positive in 19 patients (59%). Predisposing urinary tract abnormalities in recurrent UTI was shown in 12 of the hypercalciuric patients (12/32, 37.5%) and 8 of the normocalciuric patients (8/43, 19%) without a statistically significant difference between. We conclude that hypercalciuria is not a rare finding among recurrent UTI cases in Turkish children. Hypercalciuria does not modify the clinical presentation of UTI, and we suggest the investigation of urinary calcium excretion in children with recurrent UTI.

Bone mineral density and urinary N-acetyl-beta-D-glucosaminidase activity in paediatric patients with idiopathic hypercalciuria

BACKGROUND

Idiopathic hypercalciuria (IH) is defined as hypercalciuria that persists after correction of dietary inbalances and has no detectable causes. Patients with IH have a higher prevalence of osteoporosis. Defective reabsorption of calcium by the renal tubule is considered a likely mechanism of IH. N-acetyl-beta-D-glucosaminidase (NAG) is a lysosomal enzyme that is a very sensitive marker of renal tubular impairment.

METHODS

Fifteen patients (nine boys and six girls, mean age 12.4 +/- 4.0 years) with IH (urinary calcium excretion >0.1 mmol/kg per 24 h) had their bodyweight, height, body mass index (BMI), urinary NAG/creatinine ratio (U-NAG/Cr) and 24-h urinary calcium excretion (U-Ca/24 h) assessed. L1-L4 bone mineral density (BMD) was measured by dual energy X-ray absorptiometry and volumetric BMD (BMDvol) was calculated. The obtained results were expressed as Z-scores.

RESULTS

The values of basic anthropometric parameters did not differ significantly from the values of the reference population and there was a tendency to short stature, which did not reach statistical significance (P = 0.08). The values of calciuria and U-NAG/Cr were significantly higher while BMD was significantly lower when compared to the reference values (P < 0.0006, P < 0.006 and P < 0.001, respectively). Inverse and significant correlations were found between U-Ca/24 h and BMD, U-Ca/24 h and body height, and U-Ca/24 h and BMDvol (r = -0.64 and -0.70, respectively, P < 0.01; r = -0.55, P < 0.05), while there was no correlation between U-NAG/Cr and U-Ca/24 h, nor between BMD and weight or BMD and BMI.

CONCLUSION

Tubular impairment is highly probable in children with IH, but there is a poor relationship with the degree of calcium leakage. Idiopathic hypercalciuria should be considered as a risk factor for stunted growth and low bone mass.

Growth and bone mineral density in long-lasting idiopathic hypercalciuria

Growth retardation and osteopenia have been reported in some children with idiopathic hypercalciuria (IHC), particularly in those with nephrocalcinosis. The duration of hypercalciuria might be a risk factor for osteopenia. A retrospective longitudinal analysis of statural growth and a cross-sectional evaluation of bone mineral density (BMD) was carried out in 26 IHC children followed for 4-13 years. None of the patients had nephrocalcinosis. Growth, including pubertal growth spurt, was normal in all subjects. BMD Z score less than -1 was recorded in 3 subjects with hyperuricosuria. BMD Z score averaged -0.68+/-0.99 in the 9 subjects with associated hyperuricosuria and 0.21+/-0.64 in the 17 with occasional or no hyperuricosuria ( P=0.018). Our analysis shows that children with long-lasting IHC without nephrocalcinosis have normal growth, but those with associated hyperuricosuria may be at risk for osteopenia.

Childhood stones

Urinary stones in children are usually genetic and most commonly due to hypercalciuria. Symptoms of urolithiasis in children differ among age groups. Isolated hematuria in children may be caused by hypercalciuria and precede calculus formation. Careful evaluation successfully identifies the cause of urinary stones in most children, although diagnostic criteria may vary in different age groups. Therapies should be targeted to the underlying diagnosis.

Familial microscopic hematuria caused by hypercalciuria and hyperuricosuria

We report 12 patients belonging to five different families in whom persistent isolated microhematuria was associated with hypercalciuria and/or hyperuricosuria. Four patients had episodes of gross hematuria, three patients had passed renal stones, and a history of nephrolithiasis was obtained in four of the families (80%). Calcium oxalate and uric acid crystals were commonly observed in the urine sediments. Urinary erythrocytes had a normal appearance on phase-microscopic examination. Reduction of calciuria and uricosuria by thiazide diuretics, allopurinol, forced fluid intake, and dietetic measures led to a persistent normalization of urine sediment with complete disappearance of hematuria. Determination of calcium and uric acid urinary excretions should be included in the study of familial hematuria.

Hypercalciuria preceding IgA nephropathy in a child with haematuria

We describe a child with isolated haematuria who was diagnosed and successfully treated for idiopathic hypercalciuria for 6 months, after which IgA nephropathy was demonstrated on renal biopsy performed due to the relapse of haematuria in spite of low calciuria levels. To our knowledge, this is the first case evaluated systematically in the literature shown to have IgA nephropathy while being followed up for idiopathic hypercalciuria.

Association of thin basement membrane nephropathy with hypercalciuria, hyperuricosuria and nephrolithiasis

BACKGROUND

Familial persistent microhematuria with normal renal function is the most common presentation of thin basement membrane nephropathy (TBMN). Gross hematuria episodes and loin pain attacks are other manifestations of the disease. On the other hand, it has been shown that hypercalciuria (HC) and hyperuricosuria (HU) can produce both gross or microscopic non-glomerular hematuria, in addition to their role in renal stone formation.

METHODS

We studied the prevalence of HC, HU and nephrolithiasis in a group of 27 biopsy-proven TBMN as well as in 19 non-biopsied first-degree relatives with persistent microhematuria and 25 first-degree relatives without microhematuria. A group of 27 patients with IgA nephropathy (IgAN) and persistent microhematuria, and another group of 20 healthy subjects without known renal diseases were selected as control groups.

RESULTS

Ten (37%) patients with TBMN and 8 (42%) relatives with microhematuria showed HC and/or HU at presentation; relatives without microhematuria, IgAN patients and normal controls showed a significantly lower prevalence of HC and HU. The prevalence of previous nephrolithiasis among TBMN patients (25%) was significantly higher than in IgAN patients (3%; P < 0.05). Family history of nephrolithiasis was recorded in 14 (51%) of the 27 TBMN families, in contrast with 2 of 27 (7%) with IgAN and 1 of 20 (5%) in normal controls (P < 0.05). The prevalence of nephrolithiasis, gross hematuria bouts and loin pain episodes among TBMN patients and microhematuric relatives showing HC and/or HU at presentation (44%, 44% and 27%, respectively) were significantly higher than those of TBMN patients and microhematuric relatives with normal calcium and uric acid urinary excretions (10%, 7% and 3%, respectively; P < 0.05). At the end of follow-up (8.8+/-4.1 years in TBMN patients and 9.1+/-4.2 years in relatives with microhematuria), all the cases maintained normal renal function.

CONCLUSIONS

We found a high prevalence of HC, HU, and nephrolithiasis among TBMN patients and relatives with microhematuria. Our study also shows a significant relationship between the presence of HC and/or HU and the prevalence of nephrolithiasis, gross hematuria bouts and loin pain episodes.

Renal calcification in preterm infants: follow up at 4-5 years

AIM

To determine the consequences of renal calcification in preterm infants.

METHODS

A cohort of 11 preterm babies was studied at the age of 4 to 5 years. They had had renal calcification as neonates. Seventeen matched controls were also studied. Each child had a renal ultrasound scan, a calcium load test, and a desmopressin test for renal concentrating ability (RCA). The study group also had glomerular filtration rate (GFR) estimated, using the height:creatinine ratio, and tubular phosphate reabsorption, without phosphate load, per glomerular filtration rate (Tp/GFR) calculated,

RESULTS

In the study group the median GFR was 61 ml/min/1.73m2 (range 46-79 ml/min/1.73m2) and the median calculated Tp/GFR SD score was -0.94 (range -2.8-0.68). Five children out of the study group had ultrasonic evidence of renal calcification. There was no significant difference between the two groups in renal size, calciuria, before or after calcium load, or RCA. Eight children (three patients, five controls) had an abnormal calcium load test. The RCA of the children in the study and control groups combined was below that of published values, with a median calculated SD score -0.71 (95% CI -1.21 to -0.23).

CONCLUSIONS

There was evidence of renal dysfunction in children who had been born preterm. Renal calcification detected in the neonatal period does not seem to be a major predisposing factor for the abnormalities of renal function subsequently observed in these infants.

Hypercalciuria in osteogenesis imperfecta: a follow-up study to assess renal effects

In 1991, we reported that hypercalciuria is a common finding in our pediatric patient population with osteogenesis imperfecta (OI) (17 of 47 = 36%). Here, we prospectively screened 12 of these hypercalciuric children, on average 4 years subsequent to the discovery of elevated urine calcium levels, for adverse effects on renal function. Despite an ad libitum decrease since initial investigation of about 30% in their previously normal dietary calcium intake (adjusted for body weight), 8 of the 12 patients remained hypercalciuric (urine calcium/creatinine > 0.62 mmol/mmol). We found, once again, that urinary calcium levels significantly correlated with the severity of the skeletal disease as assessed by z-score for height (r = -0.75, p = 0.005). Evaluation of kidney function, however, revealed: (i) normal routine urinalysis in all but 1 subject who had transient microscopic hematuria; (ii) unremarkable concentrating ability determined by fasting urine osmolality; (iii) normal creatinine clearance, and (iv) unremarkable ultrasonography to measure renal size and to screen for nephrocalcinosis or nephrolithiasis. Although no significant renal compromise was detected with these studies in our hypercalciuric pediatric OI patients, investigation of affected adults, especially those severely affected, will be important to assess whether this is a long-term problem and if adverse effects on the kidneys do develop.

Hematuria associated with hypercalciuria and hyperuricosuria: a practical approach

Hematuria is one of the most common urinary abnormalities found in children. When hypercalciuria was identified as a potential etiology of painless hematuria, many questions arose concerning the general importance of this observation. Subsequently, increased uric acid excretion also has been purported to cause hematuria in children. This review traces the history of these observations and describes the clinical characteristics of the clinical syndrome of hematuria associated with hypercalciuria and hyperuricosuria. Diagnostic criteria of excessive urinary excretion of calcium and uric acid are reviewed; differences in urinary calcium and uric acid excretion between infants and older children are emphasized. Aside from urolithiasis, few long-term consequences from hypercalciuria or hyperuricosuria have been identified, although some debate exists concerning the effect of chronic hypercalciuria upon bone mineralization.

Urinary incontinence due to idiopathic hypercalciuria in children

Idiopathic hypercalciuria is known to cause many nonstone urinary tract disorders in childhood. In addition to being the most common cause of microhematuria in children, our study demonstrates that idiopathic hypercalciuria is also frequently associated with urinary incontinence of all types. Of 124 children evaluated for idiopathic hypercalciuria 28 (23%) had urinary incontinence. Of the 28 children 15 (54%) had nocturnal, 6 (21%) diurnal, and 7 (25%) nocturnal and diurnal incontinence. The random urinary calcium-creatinine ratio, which was used to screen for hypercalciuria, should be part of the initial evaluation for urinary incontinence in children. Diagnosis may be confirmed by quantitative urinary calcium excretion. Most urinary incontinence in children that is due to idiopathic hypercalciuria responds to a combination of general treatment for hypercalciuria or thiazide diuretics.

Urolithiasis in pediatric patients

Urolithiasis in pediatric patients has been perceived as uncommon, and the appropriate evaluation and management have been controversial. To determine the clinical characteristics, types of stone problems, and outcomes of pediatric patients with urolithiasis encountered in a referral center, we retrospectively assessed 221 patients (113 girls and 108 boys) with urolithiasis examined at the Mayo Clinic between 1965 and 1987. The median age at onset of symptoms was 11 6/12 years among the female patients and 10 6/12 years among the male patients. Analysis of stone constituents in 122 patients showed the proportion of calcium oxalate (44.7%), calcium phosphate (23.6%), and cystine (8.1%) stones to be similar in all age-groups. Overall, struvite stones were found in 17.1% and uric acid stones in 1.6% of patients. Conditions that predisposed to metabolic urolithiasis were identified in 115 patients (52%). Hypercalciuria was confirmed in 49 of 145 patients (33.8%) and hyperoxaluria in 25 of 124 (20.2%). Eight of 96 patients had hyperuricosuria, and 5 of 54 had hypocitraturia. Forty-one patients (18.6%) had infection-related stones. Of 66 patients with structural anomalies of the genitourinary tract, 24 (36%) had metabolic abnormalities and 26 (39%) had chronic infection. Among patients with chronic infection, 29% had metabolic abnormalities. Of the 221 patients, 148 (67%) had two or more stones during a mean follow-up of 59 months. Among 140 patients with 12 months or more of follow-up, metabolic activity was present in 31 (22.1%) at the time of most recent examination. Overall, 166 of 221 children (75.1%) were found to have factors that predisposed to urolithiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Family investigations in idiopathic hypercalciuria

We analysed some genetic and environmental factors influencing renal (RH) and absorptive hypercalciuria (AH) the main subtypes of idiopathic hypercalciuria (IH). Their distinction is essential in the prevention and treatment of urolithiasis. Twenty-one children admitted for renal stones had IH (8 RH and 13 AH). Their families were investigated with the participation of a total of 68 family members including 62 first-degree relatives. They were all normocalcaemic. Their urinary calcium excretion was measured on at least two occasions, and they underwent a calcium restriction--calcium loading test. Each subject was interviewed with reference to medical history, drug administration, social conditions, and nutritional habits. Pedigree analysis suggested a higher rate of familiarity and autosomal dominant inheritance of RH whereas no such pattern was found among the relatives of patients with AH. The interviews disclosed a distinct preference for calcium-rich foods in subjects with AH, while RH and normocalciuric individuals preferred a low-calcium diet. We conclude that the subtypes of IH are genetically different. RH is most probably inherited as an autosomal dominant trait (or has at least an autosomal dominant form), whereas AH is more likely to be associated with nutritional factors.

Renal function in children with idiopathic hypercalciuria

Abnormalities in renal tubular function have been reported in adult patients with idiopathic renal hypercalciuria. To determine if such abnormalities are present early in the natural history of renal hypercalciuria, we evaluated renal tubular function in ten children with idiopathic renal hypercalciuria, aged 5-17 years. Seven of the children presented with urolithiasis and three with hematuria. Urinary calcium excretion ranged from 4 to 9 mg/kg per day, (5.2 +/- 0.5, mean +/- SEM) with a mean fasting urinary calcium to creatinine ration of 0.31 +/- 0.03. Studies described in this report were performed after 1 week of ingesting a diet containing 1,000 mg calcium, 3,000 mg sodium, and 100 mg purine. Clearance of creatinine ranged from 84 to 159 ml/min per 1.73 m2. Tm phosphate (mg/100 ml GFR) was normal in each child (mean 4.66 +/- 0.06 mg/100 ml GFR). Fractional excretion of uric acid, sodium and beta-2-microglobulin were also normal in each child. Serum bicarbonate concentrations ranged from 21.5 to 27 mEq/l with a mean of 24.4 +/- 0.5 mEq/l and all patients lowered urinary pH to less than 5.5. Hypotonic diuresis demonstrated normal free water clearance with a mean of 12.8 ml/min per 100 ml Cin. Distal sodium delivery and fractional distal sodium reabsorption were normal with a mean of 13.6 +/- 1.2% and 92.7 +/- 0.5%, respectively. Water deprivation studies demonstrated a range of maximum urinary osmolality from 711 to 1,020 mosmol/kg H2O with a mean of 864 +/- 34 mosmol/kg H2O. Seven healthy children, ingesting an identical study diet, concentrated their urine to a mean of 1,059 +/- 31 mosmol/kg h2O.(ABSTRACT TRUNCATED AT 250 WORDS)