Protein Quality Control of NKCC2 in Bartter Syndrome and Blood Pressure Regulation.

Mutations in NKCC2 generate antenatal Bartter syndrome type 1 (type 1 BS), a life-threatening salt-losing nephropathy characterized by arterial hypotension, as well as electrolyte abnormalities. In contrast to the genetic inactivation of NKCC2, inappropriate increased NKCC2 activity has been associated with salt-sensitive hypertension. Given the importance of NKCC2 in salt-sensitive hypertension and the pathophysiology of prenatal BS, studying the molecular regulation of this Na-K-2Cl cotransporter has attracted great interest. Therefore, several studies have addressed various aspects of NKCC2 regulation, such as phosphorylation and post-Golgi trafficking. However, the regulation of this cotransporter at the pre-Golgi level remained unknown for years. Similar to several transmembrane proteins, export from the ER appears to be the rate-limiting step in the cotransporter's maturation and trafficking to the plasma membrane. The most compelling evidence comes from patients with type 5 BS, the most severe form of prenatal BS, in whom NKCC2 is not detectable in the apical membrane of thick ascending limb (TAL) cells due to ER retention and ER-associated degradation (ERAD) mechanisms. In addition, type 1 BS is one of the diseases linked to ERAD pathways. In recent years, several molecular determinants of NKCC2 export from the ER and protein quality control have been identified. The aim of this review is therefore to summarize recent data regarding the protein quality control of NKCC2 and to discuss their potential implications in BS and blood pressure regulation.

[Cystic fibrosis primarily presenting with pseudo-Bartter syndrome: a report of three cases and literature review]. / 以假性Bartter综合征为主要表现的囊性纤维化患儿3ä¾‹å¹¶æ–‡çŒ®å¤ä¹ .

OBJECTIVES: To summarize the clinical characteristics and genetic variations in children with cystic fibrosis (CF) primarily presenting with pseudo-Bartter syndrome (CF-PBS), with the aim to enhance understanding of this disorder. METHODS: A retrospective analysis was performed on the clinical data of three children who were diagnosed with CF-PBS in Hunan Children's Hospital from January 2018 to August 2023, and a literature review was performed. RESULTS: All three children had the onset of the disease in infancy. Tests after admission showed hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis, and genetic testing showed the presence of compound heterozygous mutation in the CFTR gene. All three children were diagnosed with CF. Literature review obtained 33 Chinese children with CF-PBS, with an age of onset of 1-36 months and an age of diagnosis of 3-144 months. Among these children, there were 29 children with recurrent respiratory infection or persistent pneumonia (88%), 26 with malnutrition (79%), 23 with developmental retardation (70%), and 18 with pancreatitis or extrapancreatic insufficiency (55%). Genetic testing showed that c.2909G>A was the most common mutation site of the CFTR gene, with a frequency of allelic variation of 23% (15/66). CONCLUSIONS: CF may have no typical respiratory symptoms in the early stage. The possibility of CF-PBS should be considered for infants with recurrent hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis, especially those with malnutrition and developmental retardation. CFTR genetic testing should be performed as soon as possible to help with the diagnosis of CF.

Polymyxin B-induced Bartter syndrome.

Bartter syndrome is a genetic disorder characterised by chloride-unresponsive metabolic alkalosis, hypokalaemia, hypomagnesaemia and hypercalciuria. While it commonly presents antenatally or in early infancy, sometimes, drugs can induce a state similar to Bartter syndrome in any age group, called acquired Bartter syndrome. Polymyxins and aminoglycosides are the most commonly implicated drugs. Polymyxin B and polymyxin E (popularly known as colistin) are the two chemically similar polymyxins that are commonly used clinically. While colistin is frequently associated with nephrotoxicity, polymyxin B is generally considered less nephrotoxic. This difference is due to the way these two drugs are handled by the kidneys. In this case report, we discuss a middle-aged male who developed Bartter syndrome due to polymyxin B, which resolved on discontinuation of the drug, and re-appeared after its re-introduction later. This case exemplifies the nephrotoxicity caused by polymyxin B and the need for vigilance when using this drug.

Adult classic Bartter syndrome: a case report with 5-year follow-up and literature review.

Bartter syndrome (BS) is a rare, inherited salt-losing renal tubular disorder characterized by secondary hyperaldosteronism, hypokalemia, hypochloremia, metabolic alkalosis, and low-to-normal blood pressure. Classic BS, or BS Type 3, the most common subtype in the Asian population, is caused by a molecular defect in ClC-Kb, a voltage-gated chloride channel in renal tubules, due to CLCNKB gene mutation. Because the onset of BS is more common in children than in adults, the diagnosis, treatment outcomes, genotype/phenotype association, and follow-up of adult-onset BS Type 3 are limited. This case report describes the findings in a 20-year-old man who was admitted with hypokalemic paralysis, with clinical manifestations were similar to those of Gitelman syndrome (GS); however, the patient was later diagnosed to have BS Type 3 through genetic testing (NM_000085.4 (CLCNKB): c.1052G>T). A literature review showed that no homozygous mutations have been reported to date. After 5 years of treatment and follow-up, we found that this genotype requires high levels of potassium and is prone to urinary protein and metabolic syndrome. Distinguishing adult-onset BS from GS is challenging in clinical practice. However, genetic diagnosis can help solve this problem effectively, and genotypes play a guiding role in treatment planning.

AUP1 Regulates the Endoplasmic Reticulum-Associated Degradation and Polyubiquitination of NKCC2.

Inactivating mutations of kidney Na-K-2Cl cotransporter NKCC2 lead to antenatal Bartter syndrome (BS) type 1, a life-threatening salt-losing tubulopathy. We previously reported that this serious inherited renal disease is linked to the endoplasmic reticulum-associated degradation (ERAD) pathway. The purpose of this work is to characterize further the ERAD machinery of NKCC2. Here, we report the identification of ancient ubiquitous protein 1 (AUP1) as a novel interactor of NKCC2 ER-resident form in renal cells. AUP1 is also an interactor of the ER lectin OS9, a key player in the ERAD of NKCC2. Similar to OS9, AUP1 co-expression decreased the amount of total NKCC2 protein by enhancing the ER retention and associated protein degradation of the cotransporter. Blocking the ERAD pathway with the proteasome inhibitor MG132 or the α-mannosidase inhibitor kifunensine fully abolished the AUP1 effect on NKCC2. Importantly, AUP1 knock-down or inhibition by overexpressing its dominant negative form strikingly decreased NKCC2 polyubiquitination and increased the protein level of the cotransporter. Interestingly, AUP1 co-expression produced a more profound impact on NKCC2 folding mutants. Moreover, AUP1 also interacted with the related kidney cotransporter NCC and downregulated its expression, strongly indicating that AUP1 is a common regulator of sodium-dependent chloride cotransporters. In conclusion, our data reveal the presence of an AUP1-mediated pathway enhancing the polyubiquitination and ERAD of NKCC2. The characterization and selective regulation of specific ERAD constituents of NKCC2 and its pathogenic mutants could open new avenues in the therapeutic strategies for type 1 BS treatment.

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.

Pseudo-Bartter syndrome as the initial presentation of cystic fibrosis in children: an important diagnosis not to be missed.

Pseudo-Bartter syndrome (PBS) is characterised by hyponatraemic, hypochloraemic metabolic alkalosis that mimics Bartter syndrome, without renal tubular disease. We present a case of an infant with a positive cystic fibrosis (CF) newborn screening, hospitalised during the summer with dehydration, oliguria and apathy. Blood analysis revealed hypochloraemic metabolic alkalosis, hypokalaemia and hyponatraemia. Urine analysis showed leucocyturia with reduced sodium and chloride excretion fraction, and urinary culture was positive for Citrobacter koseri After antibiotherapy and intravenous rehydration with additional supplementation of sodium and chloride, the patient recovered completely. PBS is one of CF complications that is especially prevalent in infants and young children with increased sweating and/or other causes of additional loss of sodium and chloride. Clinical awareness of this syndrome and its strong clinical suspicion are extremely important for an early diagnosis and treatment of CF, particularly in countries where the universal screening of CF is not routinely performed.

Identification of a novel intronic mutation of MAGED2 gene in a Chinese family with antenatal Bartter syndrome.

BACKGROUND: Antenatal Bartter syndrome is a life-threatening disease caused by a mutation in the MAGED2 gene located on chromosome Xp11. It is characterized by severe polyhydramnios and extreme prematurity. While most reported mutations are located in the exon region, variations in the intron region are rarely reported. METHODS: In our study, we employed whole exome sequencing and Sanger sequencing to genotype members of this family. Additionally, a minigene assay was conducted to evaluate the impact of genetic variants on splicing. RESULTS: Our findings reveal a novel intronic variant (NM_177433.3:c.1271 + 4_1271 + 7delAGTA) in intron 10 of the MAGED2 gene. Further analysis using the minigene assay demonstrated that this variant activated an intronic cryptic splice site, resulting in a 96 bp insertion in mature mRNA. CONCLUSIONS: Our results indicate that the novel intronic variant (c.1271 + 4_1271 + 7delAGTA) in intron 10 of the MAGED2 gene is pathogenic. This expands the mutation spectrum of MAGED2 and highlights the significance of intronic sequence analysis.

Recurrent transient severe hypocalcaemia in two siblings with type 1 Bartter syndrome.

Type 1 Bartter syndrome causes hypokalaemia and metabolic alkalosis owing to mutation in the SLC12A1 gene. Meanwhile, hypocalcaemia is rare in Bartter syndrome, except in type 5 Bartter syndrome. Herein, we describe two siblings with type 1 Bartter syndrome with recurrent transient severe hypocalcaemia. They each visited our hospital several times with chief complaints of numbness in the limbs, shortness of breath and tetany after stresses such as exercise or fever. Severe hypocalcaemia was also observed with a serum calcium level of approximately 6.0 mg/dL at each visit. The clinical symptoms and abnormalities in laboratory findings quickly improved with rest and intravenous treatment. In a steady state, no severe hypocalcaemia was evident, but serum intact parathyroid hormone (PTH) levels were high. In recent years, a large-scale study has revealed that type 1 and type 2 Bartter syndrome have high PTH values. In addition, there are reports that these patients develop hypocalcaemia due to PTH resistance. Therefore, our patient was also in a PTH-resistant state, and hypocalcaemia was thought to be exacerbated by physical stress. It is not well known that Bartter syndrome patients other than those with type 5 suffer from hypocalcaemia. And hypocalcaemia was not detected in normal examinations under steady-state conditions. Therefore, in patients with type 1 and type 2 Bartter syndrome, severe hypocalcaemia may occur, but may go unnoticed. When following up these patients, the attending physician must keep in mind that such patients are in a PTH-resistant state and that physical stress can cause severe hypocalcaemia.

Mitochondrial Dysfunction in Kidney Tubulopathies.

Mitochondria play a key role in kidney physiology and pathology. They produce ATP to fuel energy-demanding water and solute reabsorption processes along the nephron. Moreover, mitochondria contribute to cellular health by the regulation of autophagy, (oxidative) stress responses, and apoptosis. Mitochondrial abundance is particularly high in cortical segments, including proximal and distal convoluted tubules. Dysfunction of the mitochondria has been described for tubulopathies such as Fanconi, Gitelman, and Bartter-like syndromes and renal tubular acidosis. In addition, mitochondrial cytopathies often affect renal (tubular) tissues, such as in Kearns-Sayre and Leigh syndromes. Nevertheless, the mechanisms by which mitochondrial dysfunction results in renal tubular diseases are only scarcely being explored. This review provides an overview of mitochondrial dysfunction in the development and progression of kidney tubulopathies. Furthermore, it emphasizes the need for further mechanistic investigations to identify links between mitochondrial function and renal electrolyte reabsorption.

Clinical Research on Rett Syndrome: Central Hypoxemia and Hypokalemic Metabolic Alkalosis.

Background: Rett syndrome (RTT) is now widely recognized as a profound neurological disorder that predominantly affects females and is closely associated with mutations in the methylated CpG binding protein 2 (MECP2) gene located on the X chromosome. The Characteristic symptoms of RTT include the loss of acquired language and motor skills, repetitive hand movements, irregular breathing, and seizures. Additionally, RTT patients may experience sporadic episodes of gastrointestinal problems, hypoplasia, early-onset osteoporosis, bruxism, and screaming episodes. It is worth noting that males exhibit a unique and variable phenotype, though rare in RTT cases, often accompanied by severe manifestations. Case Presentation: In this report, we present the case of a young male child with a de novo c.806delG hemizygous mutation, leading to an atypical presentation of RTT that remarkably mirrors the clinical features of Bartter syndrome, a genetic metabolic disorder. The clinical manifestations in this case included the loss of previously acquired language and motor skills, repetitive hand movements, breathing irregularities, seizures, sporadic episodes of gastrointestinal distress, hypoplasia, early-onset osteoporosis, bruxism, and episodes of screaming. This distinctive presentation underscores the complex diagnostic landscape of RTT, particularly in males, and highlights the need for vigilant clinical evaluation. Conclusions: This case report sheds light on an unusual and atypical presentation of RTT in a young male child with a de novo c.806delG hemizygous mutation. The resemblance of clinical features to Bartter syndrome underscores the diagnostic challenges posed by RTT and highlights the importance of comprehensive clinical assessment and genetic testing, especially in cases deviating from the typical RTT phenotype. Our findings contribute valuable insights into the early diagnosis and management of atypical RTT presentations.

Successful antenatal treatment of MAGED2-related Bartter syndrome and review of treatment options and efficacy.

A new form of transient antenatal Bartter syndrome (aBS) was recently identified that is associated with the X-linked MAGED2 variant. Case reports demonstrate that this variant leads to severe polyhydramnios that may result in preterm birth or pregnancy loss. There is limited but promising evidence that amnioreductions may improve fetal outcomes in this rare condition. We report a woman with two affected pregnancies. In the first pregnancy, the patient was diagnosed with mild-to-moderate polyhydramnios in the second trimester that ultimately resulted in preterm labor and delivery at 25 weeks with fetal demise. Whole exome sequencing of the amniotic fluid sample resulted after the pregnancy loss and revealed a c.1337G>A MAGED2 variant that was considered diagnostically. The subsequent pregnancy was confirmed by chorionic villi sampling to also be affected by this variant. The pregnancy was managed with frequent ultrasounds and three amnioreductions that resulted in spontaneous vaginal delivery at 37 weeks and 6 days of a viable newborn with no evidence of overt electrolyte abnormalities suggesting complete resolution. A detailed review of the published cases of MAGED2-related transient aBS is provided. Our review focuses on individuals who received antenatal treatment. A total of 31 unique cases of MAGED2-related transient aBS were compiled. Amnioreduction was performed in 23 cases and in 18 cases no amnioreduction was performed. The average gestational age at delivery was significantly lower in cases without serial amnioreduction (28.7 vs. 30.71 weeks, p = 0.03). Neonatal mortality was seen in 5/18 cases without serial amnioreduction, and no mortality was observed in the cases with serial amnioreduction. In cases of second trimester severe polyhydramnios without identifiable cause, whole exome sequencing should be considered. Intensive ultrasound surveillance and serial amnioreduction is recommended for the management of MAGED2-related transient aBS.

Expanding Genotype-Phenotype Correlation of CLCNKA and CLCNKB Variants Linked to Hearing Loss.

The ClC-K channels CLCNKA and CLCNKB are crucial for the transepithelial transport processes required for sufficient urinary concentrations and sensory mechanoelectrical transduction in the cochlea. Loss-of-function alleles in these channels are associated with various clinical phenotypes, ranging from hypokalemic alkalosis to sensorineural hearing loss (SNHL) accompanied by severe renal conditions, i.e., Bartter's syndrome. Using a stepwise genetic approach encompassing whole-genome sequencing (WGS), we identified one family with compound heterozygous variants in the ClC-K channels, specifically a truncating variant in CLCNKA in trans with a contiguous deletion of CLCNKA and CLCNKB. Breakpoint PCR and Sanger sequencing elucidated the breakpoint junctions derived from WGS, and allele-specific droplet digital PCR confirmed one copy loss of the CLCNKA_CLCNKB contiguous deletion. The proband that harbors the CLCNKA_CLCNKB variants is characterized by SNHL without hypokalemic alkalosis and renal anomalies, suggesting a distinct phenotype in the ClC-K channels in whom SNHL predominantly occurs. These results expanded genotypes and phenotypes associated with ClC-K channels, including the disease entities associated with non-syndromic hearing loss. Repeated identification of deletions across various extents of CLCNKA_CLCNKB suggests a mutational hotspot allele, highlighting the need for an in-depth analysis of the CLCNKA_CLCNKB intergenic region, especially in undiagnosed SNHL patients with a single hit in CLCNKA.

Long-Term Indomethacin Treatment in a Chinese Child with Gitelman Syndrome: Case Report and Literature Review on its Efficacy and Tolerance.

BACKGROUND Gitelman syndrome (GS) is a rare inherited autosomal recessive salt-losing renal tubulopathy. Early-onset GS is difficult to differentiate from Bartter syndrome (BS). It has been reported in some cases that cyclooxygenase (COX) inhibitors, which pharmacologically reduce prostaglandin E2(PGE2) synthesis, are helpful for GS patients, especially in children, but the long-term therapeutic effect has not yet been revealed. CASE REPORT A 4-year-old boy was first brought to our hospital for the chief concern of short stature and growth retardation. Biochemical tests demonstrated severe hypokalemia, hyponatremia, and hypochloremic metabolic alkalosis. The patient's serum magnesium was normal. He was diagnosed with BS and treated with potassium supplementation and indomethacin and achieved stable serum potassium levels and slow catch-up growth. At 11.8 years of age, the patient showed hypomagnesemia and a genetic test confirmed that he had GS with compound heterozygous mutations in the SLC12A3 gene. At the age of 14.8 years, when indomethacin had been taken for nearly 10 years, the boy reported having chronic stomachache, while his renal function remained normal. After proton pump inhibitor and acid inhibitor therapy, the patient's symptoms were ameliorated, and he continued to take a low dose of indomethacin (37.5 mg/d divided tid) with good tolerance. CONCLUSIONS Early-onset GS in childhood can be initially misdiagnosed as BS, and gene detection can confirm the final diagnosis. COX inhibitors, such as indomethacin, might be tolerated by pediatric patients, and long-term therapy can improve the hypokalemia and growth retardation without significant adverse effects.

Genome mining yields putative disease-associated ROMK variants with distinct defects.

Bartter syndrome is a group of rare genetic disorders that compromise kidney function by impairing electrolyte reabsorption. Left untreated, the resulting hyponatremia, hypokalemia, and dehydration can be fatal, and there is currently no cure. Bartter syndrome type II specifically arises from mutations in KCNJ1, which encodes the renal outer medullary potassium channel, ROMK. Over 40 Bartter syndrome-associated mutations in KCNJ1 have been identified, yet their molecular defects are mostly uncharacterized. Nevertheless, a subset of disease-linked mutations compromise ROMK folding in the endoplasmic reticulum (ER), which in turn results in premature degradation via the ER associated degradation (ERAD) pathway. To identify uncharacterized human variants that might similarly lead to premature degradation and thus disease, we mined three genomic databases. First, phenotypic data in the UK Biobank were analyzed using a recently developed computational platform to identify individuals carrying KCNJ1 variants with clinical features consistent with Bartter syndrome type II. In parallel, we examined genomic data in both the NIH TOPMed and ClinVar databases with the aid of Rhapsody, a verified computational algorithm that predicts mutation pathogenicity and disease severity. Subsequent phenotypic studies using a yeast screen to assess ROMK function-and analyses of ROMK biogenesis in yeast and human cells-identified four previously uncharacterized mutations. Among these, one mutation uncovered from the two parallel approaches (G228E) destabilized ROMK and targeted it for ERAD, resulting in reduced cell surface expression. Another mutation (T300R) was ERAD-resistant, but defects in channel activity were apparent based on two-electrode voltage clamp measurements in X. laevis oocytes. Together, our results outline a new computational and experimental pipeline that can be applied to identify disease-associated alleles linked to a range of other potassium channels, and further our understanding of the ROMK structure-function relationship that may aid future therapeutic strategies to advance precision medicine.

Bartter Syndrome: A Systematic Review of Case Reports and Case Series.

Background and Objectives: Bartter syndrome (BS) is a rare group of autosomal-recessive disorders that usually presents with hypokalemic metabolic alkalosis, occasionally with hyponatremia and hypochloremia. The clinical presentation of BS is heterogeneous, with a wide variety of genetic variants. The aim of this systematic review was to examine the available literature and provide an overview of the case reports and case series on BS. Materials and Methods: Case reports/series published from April 2012 to April 2022 were searched through Pubmed, JSTOR, Cochrane, ScienceDirect, and DOAJ. Subsequently, the information was extracted in order to characterize the clinical presentation, laboratory results, treatment options, and follow-up of the patients with BS. Results: Overall, 118 patients, 48 case reports, and 9 case series (n = 70) were identified. Out of these, the majority of patients were male (n = 68). A total of 21 patients were born from consanguineous marriages. Most cases were reported from Asia (73.72%) and Europe (15.25%). In total, 100 BS patients displayed the genetic variants, with most of these being reported as Type III (n = 59), followed by Type II (n = 19), Type I (n = 14), Type IV (n = 7), and only 1 as Type V. The most common symptoms included polyuria, polydipsia, vomiting, and dehydration. Some of the commonly used treatments were indomethacin, potassium chloride supplements, and spironolactone. The length of the follow-up time varied from 1 month to 14 years. Conclusions: Our systematic review was able to summarize the clinical characteristics, presentation, and treatment plans of BS patients. The findings from this review can be effectively applied in the diagnosis and patient management of individuals with BS, rendering it a valuable resource for nephrologists in their routine clinical practice.

Pattern of hereditary renal tubular disorders in Egyptian children.

BACKGROUND: Hereditary renal tubular disorders (HRTD) represent a group of genetic diseases characterized by disturbances in fluid, electrolyte, and acid-base homeostasis. There is a paucity of studies on pediatric HRTD in Egypt. In this study, we aimed to study the pattern, characteristics, and growth outcome of HRTD at an Egyptian medical center. METHODS: This study included children from one month to < 18-years of age with HRTD who were diagnosed and followed up at the Pediatric Nephrology Unit of Sohag University Hospital from January 2015 to December 2021. Data on patients` demographics, clinical features, growth profiles, and laboratory characteristics were collected. RESULTS: Fifty-eight children (57% males; 72% parental consanguinity; 60% positive family history) were diagnosed with seven HRTD types. The most commonly encountered disorders were distal renal tubular acidosis (distal renal tubular acidosis [RTA] 27 cases, 46.6%) and Bartter syndrome (16 cases 27.6%). Other identified disorders were Fanconi syndrome (6 cases with cystinosis), isolated proximal RTA (4 cases), nephrogenic diabetes insipidus (3 cases), and one case for each RTA type IV and Gitelman syndrome. The median age at diagnosis was 17 months with a variable diagnostic delay. The most common presenting features were failure to thrive (91.4%), developmental delay (79.3%), and dehydration episodes (72.4%). Most children showed marked improvement in growth parameters in response to appropriate management, except for cases with Fanconi syndrome. Last, only one case (with cystinosis) developed end-stage kidney disease. CONCLUSIONS: HRTD (most commonly distal RTA and Bartter syndrome) could be relatively common among Egyptian children, and the diagnosis seems challenging and often delayed.

Genotypic variability in patients with clinical diagnosis of Bartter syndrome type 3.

Bartter syndrome (BS) is a salt-losing hereditary tubulopathy characterized by hypokalemic metabolic alkalosis with secondary hyperaldosteronism. Confirmatory molecular diagnosis may be difficult due to genetic heterogeneity and overlapping of clinical symptoms. The aim of our study was to describe the different molecular findings in patients with a clinical diagnosis of classic BS. We included 27 patients (26 families) with no identified pathogenic variants in CLCNKB. We used a customized Ion AmpliSeq Next-Generation Sequencing panel including 44 genes related to renal tubulopathies. We detected pathogenic or likely pathogenic variants in 12 patients (44%), reaching a conclusive genetic diagnosis. Variants in SLC12A3 were found in 6 (Gitelman syndrome). Median age at diagnosis was 14.6 years (range 0.1-31), with no history of prematurity or polyhydramnios. Serum magnesium level was low in 2 patients (33%) but urinary calcium excretion was normal or low in all, with no nephrocalcinosis. Variants in SLC12A1 were found in 3 (BS type 1); and in KCNJ1 in 1 (BS type 2). These patients had a history of polyhydramnios in 3 (75%), and the mean gestational age was 34.2 weeks (SD 1.7). The median age at diagnosis was 1.8 years (range 0.1-6). Chronic kidney disease and nephrocalcinosis were present in 1 (25%) and 3 (75%) patients, respectively. A variant in CLCN5 was found in one patient (Dent disease), and in NR3C2 in another patient (Geller syndrome). Genetic diagnosis of BS is heterogeneous as different tubulopathies can present with a similar clinical picture. The use of gene panels in these diseases becomes more efficient than the study gene by gene with Sanger sequencing.