Tacrolimus ameliorates the phenotypes of type 4 Bartter syndrome model mice through activation of sodium-potassium-2 chloride cotransporter and sodium-chloride cotransporter.

Type 4 Bartter syndrome (BS) is caused by genetic mutations in barttin, which is coded for by BSND. Barttin serves as the ß-subunit of the ClC-K chloride (Cl-) channel, which is widely expressed in distal nephrons. Type 4 BS is characterized by severely impaired reabsorption of salt, which may cause polyuria, hypokalemia, and metabolic alkalosis. Calcineurin inhibitors reportedly induce renal salt retention and hyperkalemia by enhancing the phosphorylation of the sodium (Na+)-potassium (K+)-2Cl- cotransporter (NKCC2) and Na+-Cl- cotransporter (NCC). In addition, we have previously reported that tacrolimus, a calcineurin inhibitor, increases the levels of phosphorylated NCC. In this study, we administered tacrolimus to barttin hypomorphic (Bsndneo/neo) mice, a murine model of type 4 BS that exhibits polyuria, hypokalemia, and metabolic alkalosis. Administration of tacrolimus increased the serum K+ level and suppressed urinary K+ excretion. Furthermore, after treatment with tacrolimus, Bsndneo/neo mice increased levels of phosphorylated NCC and NKCC2. We conclude that tacrolimus partially improves clinical phenotypes of Bsndneo/neo mice, and that calcineurin inhibitors might be effective for treating type 4 BS.

Effect of nonsteroidal anti-inflammatory drugs in children with Bartter syndrome.

BACKGROUND: Bartter syndrome (BS) is a salt-wasting tubulopathy with induced expression of cyclooxygenase-2 in the macula densa, leading to increased prostaglandin production and hyperreninemia. Nonsteroidal anti-inflammatory drugs (NSAIDs) are currently used in BS; however, there is limited information on the impact of NSAIDs at treatment initiation or the potential utility of plasma renin level to guide therapy in patients with BS. METHODS: We included 19 patients with BS treated with NSAIDs between 1994 and 2016. We assessed serum levels of renin, aldosterone, electrolytes, calcium, phosphorus, vitamin D, and intact parathyroid hormone (iPTH) before and after treatment initiation. We also recorded modifications in sodium and potassium supplements and changes in urine calcium. RESULTS: Median age at diagnosis was 0.9 months [IQR 0-6.9]. Seven patients had BS types 1 or 2, 12 had BS type 3 and two had no mutation identified. There was a trend towards a decrease in sodium chloride supplementation after initiation of NSAIDs. When defining response to treatment based on the normalization of plasma renin level, responders had a greater reduction in their electrolytes supplementation. NSAIDs treatment was associated with a reduction in urine calcium. Before treatment, half of the patients had elevated iPTH, but iPTH normalized following initiation of NSAIDs in all but one patient. CONCLUSIONS: This study confirms that NSAIDs reduce urine wasting of sodium and calcium in patients with BS. Monitoring serum renin levels may be useful to identify the lowest effective dose of NSAIDs that optimizes reduction of urine electrolyte losses.

The Renal Outer Medullary Potassium Channel Inhibitor, MK-7145, Lowers Blood Pressure, and Manifests Features of Bartter's Syndrome Type II Phenotype.

The renal outer medullary potassium (ROMK) channel, located at the apical surface of epithelial cells in the thick ascending loop of Henle and cortical collecting duct, contributes to salt reabsorption and potassium secretion, and represents a target for the development of new mechanism of action diuretics. This idea is supported by the phenotype of antenatal Bartter's syndrome type II associated with loss-of-function mutations in the human ROMK channel, as well as, by cardiovascular studies of heterozygous carriers of channel mutations associated with type II Bartter's syndrome. Although the pharmacology of ROMK channels is still being developed, channel inhibitors have been identified and shown to cause natriuresis and diuresis, in the absence of any significant kaliuresis, on acute oral dosing to rats or dogs. Improvements in potency and selectivity have led to the discovery of MK-7145 [5,5'-((1R,1'R)-piperazine-1,4-diylbis(1-hydroxyethane-2,1-diyl))bis(4-methylisobenzofuran-1(3H)-one)], a potential clinical development candidate. In spontaneously hypertensive rats, oral dosing of MK-7145 causes dose-dependent lowering of blood pressure that is maintained during the entire treatment period, and that displays additive/synergistic effects when administered in combination with hydrochlorothiazide or candesartan, respectively. Acute or chronic oral administration of MK-7145 to normotensive dogs led to dose-dependent diuresis and natriuresis, without any significant urinary potassium losses or changes in plasma electrolyte levels. Elevations in bicarbonate and aldosterone were found after 6 days of dosing. These data indicate that pharmacological inhibition of ROMK has potential as a new mechanism for the treatment of hypertension and/or congestive heart failure. In addition, Bartter's syndrome type II features are manifested on exposure to ROMK inhibitors.

Diagnosis of antenatal Bartter syndrome.

ESTABLISHED FACTS: Bartter syndrome is a rare heterogeneous group of autosomal-recessive salt-losing renal tubular disorders that can present in fetal life (antenatal Bartter syndrome; ABS) as "unexplained" early-onset polyhydramnios, often associated with growth restriction. Prenatal diagnosis of the condition involves assessment of amniotic fluid biochemistry in a setting of polyuric polyhydramnios; with elevated chloride levels considered a consistent and diagnostic finding. Other amniotic fluid biochemical markers have been described, notably increased aldosterone levels, and low total protein levels. NOVEL INSIGHT: Antenatal Bartter syndrome is a heterogeneous group of renal disorders. While certain biochemical features in amniotic fluid might heighten suspicion, final diagnosis can only be made in the postnatal setting. In the setting of unexplained severe polyhydramnios, clinicians should continue to entertain the diagnosis of antenatal Bartter Syndrome and maintain neonatal surveillance, even if amniotic fluid markers do not support the diagnosis.

Bartter Syndrome with Normal Aldosterone Level: An Unusual Presentation.

Bartter syndrome (BS) is a hereditary disease, with an autosomal recessive or autosomal dominant mode of transmission. It is characterized by salt wasting hypochloraemic, hypokalaemic metabolic alkalosis and hyperreninaemia with normal blood pressure. The primary defect is in the thick ascending limb of loop of Henle (TAL). Herein, we report a case that had typical features of BS like severe dehydration, severe hypokalaemia, metabolic alkalosis and failure to thrive but had normal aldosterone level which is very uncommon.

Hypokalemic paralysis in a middle-aged female with classic Bartter syndrome.

Inherited classic Bartter syndrome (cBS) is an autosomal recessive renal tubular disorder resulting from inactivating mutations in the asolateral chloride channel (C1C-Kb) and usually presents in early infancy or childhood with mild to moderate hypokalemia. Profound hypokalemic paralysis in patients with cBS is extremely rare, especially in middle age. A 45-year-old Chinese female patient was referred for evaluation of chronic severe hypokalemia despite regular K+ supplementation (1 mmol/kg/d). She had had two episodes of muscle paralysis due to severe hypokalemia (K+ 1.9 - 2.1 mmol/l) in the past 3 years. She denied vomiting, diarrhea, or the use of laxatives or diuretics. Her blood pressure was normal. Biochemical studies showed hypokalemia (K+ 2.5 mmol/l) with renal potassium wasting, metabolic alkalosis (HCO3- 32 mmol/l), normomagnesemia (Mg2+ 0.8 mmol/l), hypercalciuria (calcium to creatinine ratio 0.5 mmol/mmol; normal < 0.22 mmol/mol), high plasma renin activity, but normal plasma aldosterone concentration. Abdominal sonography revealed neither renal stones nor nephrocalcinosis. Acquired causes of cBS such as autoimmune disease and drugs were all excluded. Molecular analysis of the CLCNKB gene, encoding ClC-Kb, and SLC12A3, encoding the thiazide-sensitive sodium chloride cotransporter (NCC), revealed compound heterozygous mutations in CLCNKB (L335P and G470E) inherited from her parents; her SLC12A3 was normal. These two mutations were not identified in 100 healthy subjects. Her plasma K+ concentration rose to 3 - 3.5 mmol/l after the addition of spironolactone. Inherited cBS may present with hypokalemic paralysis and should be considered in adult patients with hypokalemia and metabolic alkalosis.

Bartter syndrome-like phenotype in a patient with type 2 diabetes mellitus.

Bartter syndrome (BS) is a rare genetic tubulopathy affecting the loop of Henle leading to salt wasting. It is commonly seen in utero or in the early neonatal period. Rare cases of acquired BS are reported in association with infections like tuberculosis, granulomatous conditions like sarcoidosis, autoimmune diseases and drugs. The mainstay of management includes potassium, calcium and magnesium supplementation. We report the case of a woman in her 50s with a history of type 2 diabetes mellitus for the last 10 years, who presented with diabetic foot ulcers and generalised weakness with ECG changes suggestive of hypokalaemia. She had severe hypokalaemia with high urine potassium excretion and hypochloraemic metabolic alkalosis. She poorly responded to intravenously administered potassium supplements and had persistent hypokalaemia. On further evaluation of the persistent hypokalaemia, a diagnosis of idiopathic Bartter-like phenotype was made. She responded well to tablet indomethacin and is presently asymptomatic and is being maintained on tablet indomethacin after 6 months of follow-up.

Treatment with 17-allylamino-17-demethoxygeldanamycin ameliorated symptoms of Bartter syndrome type IV caused by mutated Bsnd in mice.

Mutations of BSND, which encodes barttin, cause Bartter syndrome type IV. This disease is characterized by salt and fluid loss, hypokalemia, metabolic alkalosis, and sensorineural hearing impairment. Barttin is the ß-subunit of the ClC-K chloride channel, which recruits it to the plasma membranes, and the ClC-K/barttin complex contributes to transepithelial chloride transport in the kidney and inner ear. The retention of mutant forms of barttin in the endoplasmic reticulum (ER) is etiologically linked to Bartter syndrome type IV. Here, we report that treatment with 17-allylamino-17-demethoxygeldanamycin (17-AAG), an Hsp90 inhibitor, enhanced the plasma membrane expression of mutant barttins (R8L and G47R) in Madin-Darby canine kidney cells. Administration of 17-AAG to Bsnd(R8L/R8L) knock-in mice elevated the plasma membrane expression of R8L in the kidney and inner ear, thereby mitigating hypokalemia, metabolic alkalosis, and hearing loss. These results suggest that drugs that rescue ER-retained mutant barttin may be useful for treating patients with Bartter syndrome type IV.

Small Molecules Targeting Kidney ClC-K Chloride Channels: Applications in Rare Tubulopathies and Common Cardiovascular Diseases.

Given the key role played by ClC-K chloride channels in kidney and inner ear physiology and pathology, they can be considered important targets for drug discovery. Indeed, ClC-Ka and ClC-Kb inhibition would interfere with the urine countercurrent concentration mechanism in Henle's loop, which is responsible for the reabsorption of water and electrolytes from the collecting duct, producing a diuretic and antihypertensive effect. On the other hand, ClC-K/barttin channel dysfunctions in Bartter Syndrome with or without deafness will require the pharmacological recovery of channel expression and/or activity. In these cases, a channel activator or chaperone would be appealing. Starting from a brief description of the physio-pathological role of ClC-K channels in renal function, this review aims to provide an overview of the recent progress in the discovery of ClC-K channel modulators.

Prenatal diagnosis of MAGED2 gene mutation causing transient antenatal Bartter syndrome.

Transient antenatal Bartter syndrome due to melanoma-associated antigen D2 gene mutation is a newly reported type of Bartter syndrome. Its characteristics include an X-linked inheritance pattern, early-onset hydramnios, and spontaneous disappearance of symptoms after childbirth. To date, there have been no reports of prenatally diagnosed cases. We herein present the case of a preterm male born to a mother with early-onset hydramnios and a family history of X-linked idiopathic hydramnios. We suspected melanoma-associated antigen D2 gene mutation and performed direct sequencing. As a result, we were able to prenatally establish a diagnosis of transient Bartter syndrome due to a melanoma-associated antigen D2 gene mutation.

Long-term follow-up of patients with Bartter syndrome type I and II.

BACKGROUND: Little information is available on a long-term follow-up in Bartter syndrome type I and II. METHODS: Clinical presentation, treatment and long-term follow-up (5.0-21, median 11 years) were evaluated in 15 Italian patients with homozygous (n = 7) or compound heterozygous (n = 8) mutations in the SLC12A1 (n = 10) or KCNJ1 (n = 5) genes. RESULTS: Thirteen new mutations were identified. The 15 children were born pre-term with a normal for gestational age body weight. Medical treatment at the last follow-up control included supplementation with potassium in 13, non-steroidal anti-inflammatory agents in 12 and gastroprotective drugs in five patients. At last follow-up, body weight and height were within normal ranges in the patients. Glomerular filtration rate was <90 mL/min/1.73 m(2) in four patients (one of them with a pathologically increased urinary protein excretion). In three patients, abdominal ultrasound detected gallstones. The group of patients with antenatal Bartter syndrome had a lower renin ratio (P < 0.05) and a higher standard deviation score (SDS) for height (P < 0.05) than a previously studied group of patients with classical Bartter syndrome. CONCLUSIONS: Patients with Bartter syndrome type I and II tend to present a satisfactory prognosis after a median follow-up of more than 10 years. Gallstones might represent a new complication of antenatal Bartter syndrome.

Case report: heavy metal burden presenting as Bartter syndrome.

CONTEXT: Maternal transfer of heavy metals during fetal development or lactation possibly contributed to the clinical manifestations of Bartter syndrome and developmental delay in the offspring. CASE PRESENTATION: An 11-month-old child diagnosed with Bartter syndrome and failure to thrive was treated concurrently for elevated metal burden while he was undergoing standard medical interventions. Treatment with body-weight doses of meso-2,3-dimercaptosuccinic acid (DMSA) reduced the body burden of lead, beryllium, copper, mercury, and cadmium at the three- and sixth-month follow-up tests. During the course of the six-month treatment, the patient gained 2.4 kg (5.2 lb) and grew approximately 9.5 cm (3.75 in). His weight shifted from significantly below the 5th percentile in weight to within the 5th percentile, and from below the 5th to within the 10th percentile for length. DISCUSSION: The child's acquisition of lead, beryllium, and copper correspond to his mother's history of stained glass assembly and occurred during fetal development or lactation, since there were no other identifiable sources that could have contributed to the heavy metal burden. Tests for known genetic mutations leading to Bartter syndrome were all negative. RELEVANCE TO CLINICAL PRACTICE: This case report highlights the potential benefit of DMSA for treatment of heavy metal body burden in infants who present with Bartter syndrome.

Eight novel KCNJ1 variants and parathyroid hormone overaction or resistance in 5 probands with Bartter syndrome type 2.

PURPOSE: Bartter syndrome type 2 (BS2) is an autosomal recessive renal tubular disorder, which is caused by the mutations in KCNJ1. This study was designed to analyze and describe the genotype and clinical features of five Chinese probands with BS2. METHODS: Identify KCNJ1 gene variants by the next generation sequencing and evaluate their mutation effects according to 2015 American College of Medical Genetics and Genomics (ACMG) standards and guidelines. RESULTS: Ten variants including eight novel ones of KCNJ1 gene were found, the most common type was missense variant. The common symptoms and signs from high to low incidence were: polydipsia and polyuria (5/5), one of them (1/5) presented with diabetes insipidus; maternal polyhydramnios and premature delivery (4/5); growth retardation (3/5). Two patients presented with hypochloremic metabolic alkalosis and hypokalemia; whereas the acid-base disturbance was absent in the others. One patient had evident parathyroid hormone (PTH) resistance (hypocalcemia, hyperphosphatemia and markedly elevated PTH levels), three presented with PTH overacting (hypercalcemia, hypophosphatemia and mild elevated PTH levels), and one showed normal blood calcium and phosphorus concentrations with high-normal PTH levels. All patients had nephrocalcinosis and/or hypercalciuria, and one of them complicated with nephrolithiasis. Indomethacin has significant therapeutic effect on the growth retardation, polydipsia and polyuria and treatment was associated with a decrease in urine calcium excretion, normalization of electrolyte disturbance and PTH parameters. CONCLUSIONS: Ten variants of KCNJ1 gene were identified in five Chinese probands. These patients had atypical BS phenotype lacking evident metabolic alkalosis and/or manifesting with PTH overaction/resistance, which reminds clinicians to carefully differentiate BS2 with other parathyroid disorders. This is the first report of BS2 from Chinese populations.

Bartter syndrome with long-term follow-up: a case report.

Bartter syndrome is a rare inherited disease caused by CLCNKB mutation, which results in inactivation of the chloride channel Kb protein. Bartter syndrome is characterized by extreme hypokalemia, hypochloremia, metabolic alkalosis, hyperrenin-induced angiotensinemia, hyperaldosteronemia, and normal blood pressure. We herein report a case of Bartter syndrome that manifested as vomiting, hypokalemia, metabolic alkalosis, normal blood pressure, and significant hyperrenin-induced angiotensinemia. The patient, a 5-month-old girl, carried two known heterozygous pathogenic mutations: c.88C > T (p.Arg30*), which she had inherited from her father, and c.1313G > A (p.Arg438His), which she had inherited from her mother. Treatment with indomethacin, a nonsteroidal anti-inflammatory drug, led to rapid improvement of the hypokalemia, and treatment was continued for 14 years. The indomethacin also induced a sustainable reduction in the hypokalemia and metabolic alkalosis.

A Case of Bartter's Syndrome Presenting in Adulthood.

Bartter's syndrome is a rare disorder usually presenting antenatal or in childhood and is characterized by hypokalemia, metabolic alkalosis, hyperaldosteronism and normal blood pressure. We report a case of adult-onset Bartter's syndrome in a 38 year old male who presented with lower limb weakness.

Adjunctive acetazolamide therapy for the treatment of Bartter syndrome.

PURPOSE: Bartter syndrome is a rare hereditary salt-losing tubulopathy caused by mutations of several genes in the thick ascending limb of Henle's loop, characterized by polyuria, hypokalemic metabolic alkalosis, growth retardation and normal blood pressure. Cyclooxygenase inhibitors, potassium-sparing diuretics and angiotensin-converting enzyme inhibitors are currently used to treat electrolyte derangements, but with poor response. Whether treatment with acetazolamide, a carbonic-anhydrase inhibitor, would result in better clinical outcomes is unknown. METHODS: We randomly assigned children with Bartter syndrome in a 1:1 ratio to either receive indomethacin, enalapril, and spironolactone or indomethacin, enalapril, and spironolactone plus acetazolamide once daily in the morning for 4 weeks. After 2 days of washout, participants crossed over to receive the alternative intervention for 4 weeks. The present study examines the serum bicarbonate lowering effect of acetazolamide as an adjunctive therapy in children with Batter syndrome. RESULTS: Of the 43 patients screened for eligibility, 22 (51%), between the ages 6 and 42 months, were randomized to intervention. Baseline characteristics were similar between the two groups. Addition of acetazolamide for a period of 4 weeks significantly reduced serum bicarbonate and increased serum potassium levels, parallel with a reduction in serum aldosterone and plasma renin concentration. The 24-h urine volume, sodium, potassium, and chloride decreased significantly. CONCLUSION: Our data define a new physiologic and therapeutic role of acetazolamide for the management of children with Bartter syndrome.

Bartter syndrome representing digenic-based salt-losing tubulopathies presumably accelerated by renal insufficiency.

Bartter syndrome and Gitelman syndrome (GS) are autosomal recessive disorders usually caused by homozygous or compound heterozygous mutations in causative genes. In some patients, these two syndromes cannot be discriminated based on clinical features or mutation type; thus, a single disease concept, salt-losing tubulopathies (SLTs), has been used instead. Despite the existence of several SLT causative genes, cases of digenic heterozygous mutations in two different genes are extremely rare. Here, we report the case of a 36-year-old woman with renal insufficiency and hypokalemia caused by an SLT. To evaluate the SLT phenotype, we performed next-generation sequencing (NGS) with a gene panel including SLC12A3, SLC12A1, CLCNKB, and CLCNKA as well as laboratory examinations and diuretic loading tests. The results of the diuretic loading tests were consistent with a GS phenotype, while the NGS results showed that the patient had heterozygous mutations in SLC12A1 and CLCNKB. Both genes have been associated with BS, suggesting that the SLT was caused by digenic heterozygous mutations in two different genes. To date, only a few SLT cases caused by digenic heterozygous mutations in two different genes have been reported. The digenic SLT phenotype in the patient was presumably accelerated by moderate renal insufficiency.

Successful utilization of aliskiren, a direct renin inhibitor in Bartter syndrome.

Bartter syndrome is traditionally treated with large doses of oral potassium with or without suppression of the renin-angiotensin system. Since plasma renin activity is invariably elevated in Bartter syndrome, the availability of the direct renin inhibitor aliskiren should lead to the ability to maintain potassium levels without utilizing large doses of oral potassium. This case report is, to my knowledge, the first to show the efficacy of a renin receptor blocker in Bartter syndrome.