Hypercalciuria with Bartter syndrome: evidence for an abnormality of vitamin D metabolism

Hypocalcemia as the Initial Presentation of Type 2 Bartter Syndrome: A Family Report

CONTEXT

Bartter syndrome (BS) is a group of rare autosomal-recessive tubulopathies characterized by hypokalemic, hypochloremic metabolic alkalosis in which the primary defect is a deficiency of transporters involved in sodium chloride reabsorption. Type 2 BS results from a defect in the renal outer medullary potassium channel encoded by the KCNJ1 gene. Type 2 BS presents with polyhydramnios, intrauterine growth retardation, prematurity, failure to thrive, polyuria, hypercalciuria, and life-threatening episodes of dehydration. Hypocalcemia is a very rare presenting symptom of BS, with only a few published cases reporting it as the initial manifestation of type 2 BS.

OBJECTIVE

To describe a child who presented with hypocalcemic seizure at the age of 2.3 years that was first related to vitamin D deficiency and high-phosphate soft drink consumption.

METHODS

Whole exome sequencing (WES) was used to evaluate the biochemical abnormalities of the proband.

RESULTS

We identified a previously described homozygous missense mutation c.212C>T, p.T71M in the KCNJ1 gene associated with type 2 BS. Six additional family members with the same mutation and diagnosed clinically with BS are also reported, 2 presenting with hypocalcemia associated with vitamin D deficiency.

CONCLUSION

This report expands the clinical spectrum associated with KCNJ1 mutations and emphasizes the role of WES in unsolved cases of hypocalcemia when genetic disease is suspected. It also highlights the hazardous effects of phosphate-containing soft drinks on calcium metabolism.

Parathyroid hormone and phosphate homeostasis in patients with Bartter and Gitelman syndrome: an international cross-sectional study

BACKGROUND

Small cohort studies have reported high parathyroid hormone (PTH) levels in patients with Bartter syndrome and lower serum phosphate levels have anecdotally been reported in patients with Gitelman syndrome. In this cross-sectional study, we assessed PTH and phosphate homeostasis in a large cohort of patients with salt-losing tubulopathies.

METHODS

Clinical and laboratory data of 589 patients with Bartter and Gitelman syndrome were provided by members of the European Rare Kidney Diseases Reference Network (ERKNet) and the European Society for Paediatric Nephrology (ESPN).

RESULTS

A total of 285 patients with Bartter syndrome and 304 patients with Gitelman syndrome were included for analysis. Patients with Bartter syndrome type I and II had the highest median PTH level (7.5 pmol/L) and 56% had hyperparathyroidism (PTH >7.0 pmol/L). Serum calcium was slightly lower in Bartter syndrome type I and II patients with hyperparathyroidism (2.42 versus 2.49 mmol/L; P = .038) compared to those with normal PTH levels and correlated inversely with PTH (rs -0.253; P = .009). Serum phosphate and urinary phosphate excretion did not correlate with PTH. Overall, 22% of patients had low serum phosphate levels (phosphate-standard deviation score < -2), with the highest prevalence in patients with Bartter syndrome type III (32%). Serum phosphate correlated with tubular maximum reabsorption of phosphate/glomerular filtration rate (TmP/GFR) (rs 0.699; P < .001), suggesting renal phosphate wasting.

CONCLUSIONS

Hyperparathyroidism is frequent in patients with Bartter syndrome type I and II. Low serum phosphate is observed in a significant number of patients with Bartter and Gitelman syndrome and appears associated with renal phosphate wasting.

Cisplatin Therapy Does Not Worsen Renal Function in Severe Antenatal Bartter Syndrome

A 30-year-old man with severe antenatal Bartter syndrome, diagnosed and treated in infancy, developed testicular carcinoma. Despite the known renal complications of cisplatin, this drug was used for his chemotherapy because of its superior antineoplastic effect. Nonsteroidal anti-inflammatory drug administration was continued during cisplatin therapy. Despite an increase in his oral potassium requirement, renal function was maintained following completion of chemotherapy. In spite of its significant associated nephrotoxicity, cisplatin can be used in patients with severe antenatal Bartter syndrome if required for therapy of malignancy.

Risk factors evaluation for urolithiasis among children

BACKGROUND

The prevalence of pediatric urolithiasis varies from 0.01-0.03%. Urolithiasis may be caused by anatomical, metabolic and environmental factors. Recurrence varies between 16 to 67%, and it is frequently associated with metabolic abnormalities. The objective of the present work was the identification of risk factors that promote urolithiasis in a child population.

METHODS

This study included 162 children with urolithiasis and normal renal function (mean age 7.5 years). Risk factors were investigated in two stages. In the first stage, 24-hour urine, and blood samples were analyzed to assess metabolic parameters and urinary tract infection. During the second stage, the effect of calcium restriction and a calcium load on renal Ca excretion were evaluated. Data were statistically analyzed.

RESULTS

Urolithiasis was observed in 0.02% of children, 50% of them with family history of urinary stones. There were multiple risk factors for urolithiasis including hypocitraturia (70%), hypomagnesuria (42%), hypercalciuria (37%; in 11/102 was by intestinal hyperabsorption, in 13/102 was unclassified. Ca resorption or renal Ca leak were not detected). We also detected alkaline urine (21%), systemic metabolic acidosis (20%), urinary infections (16%), nephrocalcinosis with urolithiasis (11%), oliguria (8%), urinary tract anomalies, hyperuricosemia and hypermagnesemia (7% each one), hypercalcemia (6%), hyperoxaluria (2%) and hypercystinuria (0.61%).

CONCLUSIONS

Hypocitraturia and hypomagnesuria were the most frequent risk factors associated with urolithiasis, followed by hypercalciuria. High PTH values were excluded. Children presented two or more risk factors for urolithiasis.

Understanding Bartter syndrome and Gitelman syndrome

BACKGROUND

We aim to review the clinical features of two renal tubular disorders characterized by sodium and potassium wasting: Bartter syndrome and Gitelman syndrome.

DATA SOURCES

Selected key references concerning these syndromes were analyzed, together with a PubMed search of the literature from 2000 to 2011.

RESULTS

The clinical features common to both conditions and those which are distinct to each syndrome were presented. The new findings on the genetics of the five types of Bartter syndrome and the discrete mutations in Gitelman syndrome were reviewed, together with the diagnostic workup and treatment for each condition.

CONCLUSIONS

Patients with Bartter syndrome types 1, 2 and 4 present at a younger age than classic Bartter syndrome type 3. They present with symptoms, often quite severe in the neonatal period. Patients with classic Bartter syndrome type 3 present later in life and may be sporadically asymptomatic or mildly symptomatic. The severe, steady-state hypokalemia in Bartter syndrome and Gitelman syndrome may abruptly become life-threatening under certain aggravating conditions. Clinicians need to be cognizant of such renal tubular disorders, and promptly treat at-risk patients.

Mild infantile hypercalcemia: diagnostic tests and outcomes

OBJECTIVE

To assess outcome in a cohort of patients with infantile hypercalcemia followed over 3 years.

STUDY DESIGN

Patients (n = 32) presenting to the calcium clinic between July 2002 and September 2008 were studied. In addition to tests of calcium phosphate metabolism, serum insulin-like growth factor-1, calcitonin, urine citrate, and calcium-sensing receptor gene analysis were obtained.

RESULTS

Mean age at presentation was 6.0 ± 6.3 months. Mean calcium level was 11.4 ± 0.7 mg/dL (2.84 ± 0.17 mmol/L). A recognized cause was found in 14% and a probable cause in 14% of the cohort. Those with nephrocalcinosis (n = 11) had significantly lower mean weight SDS and higher mean calcium levels. The biochemical profile of those in whom no cause could be determined included nonsuppressed parathyroid hormone with either normal or increased 1,25(OH)(2)D. Hypercalcemia resolved in 20 patients. However, in approximately a third, there was persistence in hypercalcemia, hypercalciuria, or nephrocalcinosis.

CONCLUSIONS

The addition of 1,25(OH)(2)D and calcium-sensing receptor mutation analysis to a panel of investigations may improve diagnostic yield. Clinical outcome is overall good, however, one-third need ongoing follow-up.

A novel compound heterozygous ROMK mutation presenting as late onset Bartter syndrome associated with nephrocalcinosis and elevated 1,25(OH)(2) vitamin D levels

Bartter syndrome (BS) is a rare renal tubular disorder presenting with hypokalemic metabolic alkalosis, which is classified into five types. KCNJ1 mutations usually cause the neonatal form of BS, type II BS (OMIM 241200). However, this report concerns a female patient with a novel, compound heterozygous KCNJ1 mutation that causes late-onset BS. The unique clinical findings of this case include persistently elevated 1,25(OH)(2) vitamin D levels, possibly due to increase prostaglandin E(2) levels, and medullary nephrocalcinosis. Treatment with COX-2 inhibitors resolved her hypercalciuria and improved her height and weight; renal function remains stable and there is no progression of nephrocalcinosis.

Elevated Aldosterone in Amniotic Fluid and Maternal Blood Has Diagnostic Potential in Pregnancies Complicated with a Fetus of Bartter Syndrome

Pregnancies with fetuses affected with the Bartter syndrome, an autosomal recessive disorder of hyperreninism and hyperaldosteronism, are complicated by early onset of polyhydramnios which results in preterm deliveries. We have assessed biochemical changes in amniotic fluid and the mother's blood with a view to early diagnosis. Aldosterone levels of both amniotic fluid and the mother's blood were found to be increased at 27 weeks of gestation, while electrolyte levels did not differ significantly from those reported earlier for controls. After birth the baby suffered from polyuria with hyponatremia, hypomagnesemia and hypercalciuria which could be controlled by treatment with sodium chloride and magnesium. Elevated aldosterone thus might be a useful marker for early diagnostic purposes.

Bone mineral density and bone turnover in patients with Bartter syndrome

The aim of this investigation was to evaluate bone mineral density (BMD), by use of DXA, and bone turnover, in patients with Bartter syndrome (BS). Ten patients (2 with BS type II and 8 with BS type III) were included in the procedure. Age at study varied between 2 and 30 years. During the studies usual treatment with indomethacin, spironolactone, and potassium chloride was maintained. Results were compared with those obtained in the 20 asymptomatic parents. Height of the patients at the time of the study did not differ from reference values (Z-score -1.2 to +0.8). Three patients (1 with BS type II and 2 with BS type III) presented reduced lumbar spine BMD or overt osteopenia (BMD Z-scores: -2.3, -1.3, and -1.1). BMD did not correlate significantly with age. Paternal and maternal femoral neck BMD values correlated significantly with lumbar spine BMD of the patients (r=0.65, P<0.05, and r=0.80, P<0.01). Lumbar spine BMD Z-scores correlated negatively with urinary Ca excretion when values both from patients and parents were jointly analyzed (r=-0.43, P<0.05). Plasma calcium concentration was significantly higher (P<0.001) and plasma phosphate Z-score was significantly lower (P<0.05) in the patients than in the parents. However, no significant differences were observed in values for intact PTH, 1,25 (OH)(2)D(3) and 25 (OH)D(3). Intact PTH values correlated positively with BMD Z-scores at lumbar spine (r=0.45, P<0.05) and at femoral neck (r=0.63, P<0.01). Age-corrected biochemical markers of bone formation (plasma alkaline phosphatase and osteocalcin concentrations) were normal whereas age-corrected markers of bone reabsorption (urinary PYD and DPD excretion) were significantly higher than parental values (P<0.01 and <0.05, respectively). We conclude that: (1) reduced BMD is not an exclusive feature of neonatal BS and it can be also observed in classic BS; (2) the loss of bone mineral is not progressive, probably because of the hypocalciuric effect of indomethacin therapy; and (3) this study did not determine whether loss of bone mass is the cause or the consequence of hypercalciuria although the beneficial effect of indomethacin therapy implies the latter.

Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes

Inherited hypokalemic metabolic alkalosis, or Bartter syndrome, comprises several closely related disorders of renal tubular electrolyte transport. Recent advances in the field of molecular genetics have demonstrated that there are four genetically distinct abnormalities, which result from mutations in renal electrolyte transporters and channels. Neonatal Bartter syndrome affects neonates and is characterized by polyhydramnios, premature delivery, severe electrolyte derangements, growth retardation, and hypercalciuria leading to nephrocalcinosis. It may be caused by a mutation in the gene encoding the Na-K-2Cl cotransporter (NKCC2) or the outwardly rectifying potassium channel (ROMK), a regulator of NKCC2. Classic Bartter syndrome is due to a mutation in the gene encoding the chloride channel (CLCNKB), also a regulator of NKCC2, and typically presents in infancy or early childhood with failure to thrive. Nephrocalcinosis is typically absent despite hypercalciuria. The hypocalciuric, hypomagnesemic variant of Bartter syndrome (Gitelman syndrome), presents in early adulthood with predominantly musculoskeletal symptoms and is due to mutations in the gene encoding the Na-Cl cotransporter (NCCT). Even though our understanding of these disorders has been greatly advanced by these discoveries, the pathophysiology remains to be completely defined. Genotype-phenotype correlations among the four disorders are quite variable and continue to be studied. A comprehensive review of Bartter and Gitelman syndromes will be provided here.

Biochemical examination of mother's urine is useful for prenatal diagnosis of Bartter syndrome

Bartter syndrome is characterized by renal potassium and chloride loss, hypokalaemia, hypochloraemic metabolic alkalosis and increased plasma renin activity along with elevated angiotensin II and hyperaldosteronism. For diagnosis we conducted biochemical examinations of both amniotic fluid and the mother's urine. Except for potassium, amniotic fluid electrolytes in a mother with a fetus with Bartter syndrome were high. Urinary chloride, sodium and calcium were very low. Thus, the latter parameters may allow prediction of fetal Bartter syndrome during the prenatal period.

Conjunctive effects of fibroblast growth factor and glycosaminoglycan on bone metabolism in neonatal bartter syndrome

The calciotropic activity of urine from a subject with neonatal Bartter syndrome (NBS) has been partially purified using ion-exchange and gel chromatographic techniques. A bioassay using bone disks from rat calvaria was used to estimate calciotropic activity, which in the urine of the subject with NBS appears to be due to basic fibroblast growth factor (bFGF) bound to a glycosaminoglycan susceptible to heparitinase digestion. The calciotropic activity is eluted from DEAE-Sephacel and Sepharose CL-6B in a narrow band in association with metachromatic material and is destroyed by heparitinase and blocked by an antibody to bFGF. After treatment of purified preparations with heparitinase, a component that is inactive alone but develops calciotropic activity in association with heparin can be isolated by affinity chromatography on heparin-Sepharose columns. This component is recovered from the column at NaCl concentrations expected to elute bFGF and is inactivated by antibodies to bFGF. No calciotropic activity can be shown in glycosaminoglycan-containing fractions from urine from a normal boy or a normal man, but such fractions exhibit calciotropic activity if bFGF is added to the assay system. When bFGF is added to urine from either normal subject followed by ion-exchange chromatography on DEAE-Sephacel, calciotropic activity is eluted at NaCl concentrations closely similar to those found to elute calciotropic activity from the urine of the NBS subject. It appears that the abnormal findings in NBS urine are due to excess bFGF, although they could be due to some abnormality of the glycosaminoglycan component.

[Hypercalciuria: etiologies and treatment]

Hypercalciuria is a rare biological symptom with multiple possible etiologies in children. Normal calcium excretion rate in children is defined as lower than 4 mg/kg per day, significantly higher values being observed in infants. When using urinary calcium: creatinine ratio, normal values are below 0.22 mg/mg in children, and below 0.6 to 0.8 mg/mg in infants. In our experience half patients with hypercalciuria have idiopathic hypercalciuria. Idiopathic hypercalciuria can be hereditary with a dominant autosomal mode of inheritance. Its pathophysiology is unclear, increased calcium intestinal absorption and impaired renal tubular calcium reabsorption being the two main underlying anomalies. Patients with hypercalciuria should be informed about the risk of urolithiasis and its possible prevention by a high water intake. In those patients with nephrocalcinosis or recurrent episodes of lithiasis, hydrochlorothiazide can be effective in reducing hypercalciuria. However, adverse effects of hydrochlorothiazide on serum lipids have been recently reported and make this treatment questionable in the long term.

Severe hyperchloriduria-hyperkaliuria: a new congenital renal tubular abnormality?

A female infant, aged 5 weeks, had metabolic alkalosis associated with severe electrolyte disturbances. In addition to findings typically seen in patients with Bartter syndrome or hyperprostaglandin E syndrome, she had massive urinary excretion of prostaglandins E2 and E-M, normal calcium metabolism, hyperphosphaturia, and severe hyperchloriduria and hyperkaliuria with limited response to indomethacin. These findings may represent a new congenital renal tubular abnormality.

Infantile variant of Bartter syndrome and sensorineural deafness: a new autosomal recessive disorder

The infantile variant of Bartter syndrome (IBS) is usually associated with maternal polyhydramnios, premature birth, postnatal polyuria and hypokalemic hypochloremic metabolic alkalosis and a typical appearance. IBS is thought to be an autosomal recessive trait. Several congenital tubular defects are associated with sensorineural deafness (SND). However, an association between the IBS and SND has not been reported so far. Here we describe 5 children of an extended consanguineous Bedouin family with IBS and SND. In 3 of the cases, the typical electrolyte imbalance and facial appearance were detected neonatally. SND was detected as early as age 1 month, suggesting either coincidental homozygotization of 2 recessive genes or a pleiotropic effect of one autosomal recessive gene. This association suggests that evaluation of SND is warranted in every case of IBS.

Renal calcification in the first year of life

The introduction of renal ultrasound technology has shown renal calcification to be more common in infancy than was previously believed. Understanding the role of inhibitors and promoters in crystal formation helps elucidate the pathophysiology of nephrocalcinosis. Identification of the presence or absence of hypercalcemia and hypercalciuria is an effective way to direct the diagnostic work-up of infants with nephrocalcinosis. The sonographic image of renal calcification resolves spontaneously in many infants. Whether microscopic nephrocalcinosis persists below the threshold of ultrasonographic detection is unknown. Renal calcification can be associated with persistent renal function abnormalities if hypercalciuria continues, such as in VLBW infants who receive long-term furosemide therapy after discharge from the hospital. Renal calcification may also progress to renal failure, such as in infants with primary hyperoxaluria, owing to the persistence of hyperoxaluria, a potent promoter of calcium crystal formation.

Pre-pubertal growth in the hyperprostaglandin E syndrome

Pre-pubertal body growth was followed in eight children with the hyperprostaglandin E syndrome (neonatal Bartter syndrome) treated with indomethacin over a period of 5-12 years. When corrected for prematurity, the general growth pattern was normal, with the exception of a child with delayed therapy. From the first observation (usually at birth) to the start of indomethacin, the mean height standard deviation score (SDS) corrected for prematurity changed from -0.2 to -2.8. During the first 2 years of therapy rapid catch-up growth occurred, followed by a slow adaptation of the growth pattern to that of healthy children born at term. At last observation the mean corrected height SDS was -0.5 (range -1.9 to +0.9) and the mean target height -0.9 SDS (range -1.8 to +0.1). Weight, body mass index and bone maturation also reached the normal range. No correlation was found between height SDS per year and serum potassium levels or calcium excretion. We conclude that under indomethacin treatment long-term skeletal growth of children with the hyperprostaglandin E syndrome is similar to that of other preterm children.

Nephrocalcinosis in pseudohypoaldosteronism and the effect of indomethacin therapy

We report four patients with pseudohypoaldosteronism, aged 5 months to 5 years. All patients had hypercalciuria and three had nephrocalcinosis. Two patients with nephrocalcinosis were treated with indomethacin. Polydipsia decreased and appetite and weight gain improved within 14 days of therapy. Hypercalciuria, polyuria, and creatinine clearance decreased 30% to 50% and urinary prostaglandin E2 levels decreased fourfold to eightfold.

Prostaglandin E2 alleviates cyclosporin A-induced bone loss in the rat

Cyclosporine A (CsA) administered to the male and female rat produces high-turnover osteopenia. Prostaglandins have both bone-resorbing and bone-forming properties, but administration of prostaglandin E2 (PGE2) to the rat in vivo produces a net increase in cancellous bone. To investigate the effects of PGE2 on CsA-induced alteration in bone mass, 43 male Sprague-Dawley rats (9 weeks old) were administered 15 mg/kg of CsA by oral gavage and/or 6 mg/kg of PGE2 by subcutaneous injection daily for 21 days according to the following protocol: group A was an age-matched control; group B received CsA only; group C received PGE2 only; and group D received CsA and PGE2. Serum was assayed on days 0, 7, 14, and 21 for bone gla protein (BGP), PTH, and 1,25-dihydroxyvitamin D [1,25-(OH)2D]. A computerized image analysis system was used for bone histomorphometry of the proximal tibial metaphysis after double tetracycline labeling. Compared to control animals (group A), treatment with CsA alone (group B) and PGE2 alone (group C) significantly elevated BGP levels. Combination therapy (group D) resulted in BGP levels that were significantly higher on days 7 and 14 than with either agent alone. 1,25-(OH)2D was significantly elevated in the CsA group only (group B). Therapy with CsA alone (group B) resulted in a significant osteopenia. The concurrent administration of PGE2 with CsA (group D) alleviated the altered bone mass induced by CsA alone by adding a significant amount of additional bone. This report confirms and extends the current knowledge of the different effects of CsA and PGE2 on bone mineral metabolism and demonstrates that PGE2 can alleviate the deleterious effects of CsA on bone.

Calcium homeostasis and hypercalciuria in hyperprostaglandin E syndrome

Children with hyperprostaglandin E syndrome, a neonatal variant of Bartter syndrome with enhanced renal and systemic formation of prostaglandin E2, have hypercalciuria, nephrocalcinosis, and osteopenia. Because prostaglandin E2 affects tubular calcium handling, stimulates the formation of calcitriol in vitro, and has osteolytic activity, we studied calcium homeostasis and the influence of prostaglandin E2 formation on hypercalciuria in nine patients with hyperprostaglandin E syndrome during long-term indomethacin treatment and after its withdrawal. Suppression of prostaglandin E2 formation by indomethacin resulted in improvement of biochemical and clinical features of hyperprostaglandin E syndrome. However, hypercalciuria, osteopenia, and nephrocalcinosis did not completely resolve. Despite a low calcium diet, daily urinary calcium excretion was enhanced during and after withdrawal of indomethacin treatment (median 6.3, range 5.3 to 14, and median 9.4, range 4.4 to 38 mg/kg per day, respectively). Daily urinary calcium excretion was greater after withdrawal than during indomethacin treatment. Urinary calcium excretion was not correlated with urinary prostaglandin E2 excretion. Plasma levels of intact parathyroid hormone (median 11, range 6.8 to 12 pmol/L) and calcitriol (median 157, range 108 to 236 pg/ml) were elevated during indomethacin treatment and decreased after withdrawal of indomethacin. These data suggest that hypercalciuria in hyperprostaglandin E syndrome is mainly due to a renal leak of calcium, which is caused by enhanced renal formation of prostaglandin E2 and a tubular defect not related to prostaglandin E2 formation. There is no evidence for prostaglandin-stimulated calcitriol formation. Decreasing plasma levels of parathyroid hormone in the presence of renal calcium losses after withdrawal of indomethacin treatment may be due to a bone resorption process caused by systemic prostaglandin formation; the process may contribute to hypercalciuria in the patient not receiving indomethacin.

Prostanoids in paediatric kidney diseases

Prostanoids belong to the growing family of eicosanoids, which are all derived from arachidonic acid. Prostanoids act as modulators and mediators in a large spectrum of physiological and pathophysiological processes within the kidney. On the one hand, the potent vasoconstrictor and platelet-aggregating thromboxane (TX) A2 is involved in the pathophysiology of a variety of glomerular diseases, such as haemolytic-uraemic syndrome and immune-mediated glomerulopathies. Prostaglandin (PG) E2, on the other hand, interferes with tubular electrolyte and water handling. Clinical data support the hypothesis that this member of the prostanoid family contributes to the pathophysiology of Bartter's syndrome, hyperprostaglandin E syndrome, idiopathic hypercalciuria and renal diabetes insipidus. Both prostanoids, TXA2 and PGE2, are involved in the pathophysiology of obstructive uropathies. The physiological and protective role of renal vasodilator prostanoids (PGI2 and PGE2) has been studied during treatment with non-steroidal anti-inflammatory drugs. Part of the pharmacological effects of frusemide and converting enzyme inhibitors is mediated by PGI2 and PGE2. The role of renal prostanoids in cyclosporine toxicity is still equivocal. Future investigations on the physiological and pathophysiological role of renal prostanoids will have to consider the multiple interactions between prostanoids on the one hand, and classical hormones and other mediators (e.g. cytokines) on the other hand.