Distal Renal Tubular Acidosis: ERKNet/ESPN Clinical Practice Points

[The European Rare Kidney Disease Reference Network]

Rare kidney diseases encompass a wide range of congenital, inherited and acquired conditions. Two million Europeans are affected by rare kidney diseases. The European Rare Kidney Disease Reference Network (ERKNet) aims to improve the clinical management of patients with these diseases. ERKNet encompasses 95 highly specialized adult and pediatric nephrology units at 72 sites in 24 European Union (EU) member states, as well as a group of patient advocates (European Patient Advocacy Group, ePAG). ERKNet centers care for more than 65,000 rare kidney disease patients and pursues a variety of activities. An online consultation service helps improve the management of complex cases. Expert working groups develop clinical practice guidelines for individual groups of rare kidney diseases. In a 3-year postgraduate program, junior physicians at ERKNet centers are trained by experts in the diagnosis and treatment of rare kidney diseases through webinars and case-based eLearning modules. Information brochures and online texts on rare kidney diseases for patients, relatives and the general public are produced and disseminated. Clinical research is supported by a European Registry for Rare Kidney Diseases (ERKReg), which provides important information on demographics and disease progression and facilitates the identification of patient cohorts for therapeutic studies. In addition, the registry provides clinical performance statistics of reference centers and allows benchmarking to promote the harmonization and standardization of care for rare kidney disease patients across Europe.

Neonatal Onset Distal Renal Tubular Acidosis: Description of Two Novel Variants on the ATP6V0A4 Gene and Review of the Literature on Associated Extrarenal Manifestations

Distal renal tubular acidosis (dRTA) is an extremely rare disease that affects the distal tubule's ability to excrete proton cations, acidify urine, and maintain the acid-base balance. The clinical presentation of dRTA typically includes normal anion gap metabolic acidosis with decreased serum bicarbonate levels, hypokalemia, hypercalcemia, nephrocalcinosis, and alkaline urine. Hereditary causes of dRTA include pathogenic variants in ATP6V1B1 , ATP6V0A4 , SLC4A1 , FOXI1 , and WDR72 genes, which encode different transmembrane proteins on the apical surface of type A intercalated cells in the distal tubule. Variants in these genes lead to various defects in the function of the encoded proteins and can also account for extrarenal manifestations of dRTA due to the expression of these proteins in other organs, such as the stria vascularis of the inner ear. However, the literature on extrarenal manifestations, associated renal complications of hereditary dRTA, and appropriate investigations, and follow-up for patients with dRTA is scarce. In this article, we present a challenging case of neonatal-onset dRTA and contribute two novel variants of the ATP6V0A4 gene and a novel phenotype associated with a pathogenic variant on ATP6V0A4 to the scientific community. We also review the existing literature on hereditary causes of dRTA, with emphasis on associated renal and extrarenal complications.

[What is confirmed in the treatment of metabolic acidosis in chronic kidney disease?]

Precise regulation of the acid-base balance is essential for the functioning of various organs and physiological processes. Acid retention and metabolic acidosis (MA) are frequent complications of chronic kidney disease (CKD) and can also occur following kidney transplantation. In addition to dietary modifications, pharmacological interventions, most notably sodium bicarbonate, are employed to correct MA. While several studies have reported a beneficial effect of MA correction on the progression of CKD, the results remain inconsistent and the magnitude of the treatment effect may be limited. Importantly, no beneficial effect on graft function has been demonstrated after kidney transplantation. The MA is associated with impaired bone quality and although alkali treatment has generally shown positive effects on markers of bone metabolism, consistent changes in bone density have not been observed. Additionally, MA is linked to an increased incidence of cardiovascular events but so far there is a lack of interventional studies with definitive cardiovascular endpoints. Sodium bicarbonate may lead to sodium retention, potentially increasing blood pressure, although the data on this are inconclusive. One interventional study with notable limitations reported a positive effect of alkali treatment on mortality. Correction of MA has been suggested to positively impact protein and muscle catabolism, although no improvement in physical performance was observed in a geriatric population. Limited studies exist on the endocrinological effects of alkali treatment but these indicate a favorable impact on glucose metabolism and potential benefits for thyroid function in predialysis CKD patients. Given the overall low to moderate level of evidence supporting the benefits of alkali treatment, the current guidelines from Kidney Disease: Improving Global Outcomes (KDIGO) propose alkali treatment to prevent serum bicarbonate levels < 18 mmol/l (prior < 22 mmol/l) in adults and the resulting complications.

Fanconi-Bickel syndrome complicated by nephrocalcinosis and GFR decline

Fanconi-Bickel syndrome (FBS) is a rare genetic disorder of carbohydrate metabolism due to pathogenic variants in SLC2A2, a gene encoding glucose transporter 2 (GLUT2), which leads to accumulation of glycogen in the kidney and liver. While consequential complex proximal tubular dysfunction is well acknowledged in the literature, long-term trajectories of kidney function in patients with FBS have not been well characterized, and kidney biopsy is performed infrequently. Here, we report on a patient with FBS followed from infancy through young adulthood who presented early on with hypercalciuria, phosphaturia, and hypophosphatemia, complicated by chronic kidney disease development during childhood. Kidney biopsy, in addition to a widespread glycogen accumulation in proximal tubular epithelial cells, demonstrated medullary nephrocalcinosis. Screening for nephrocalcinosis may be warranted in pediatric patients with FBS, along with close surveillance of their kidney function.

Recent Developments in the Treatment of Pediatric Distal Renal Tubular Acidosis

Distal renal tubular acidosis (dRTA) is characterized by a primary defect in proton secretion by α-intercalated cells of the collecting duct, leading to impaired urine acidification and resulting in metabolic acidosis, hypokalemia, and hypercalciuria. Inherited forms of dRTA are currently associated with variants in five genes (SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, and WDR72), each being associated with specific extra-renal manifestations. Acquired forms can result from autoimmune diseases or drug side effects. Classical complications include nephrolithiasis, nephrocalcinosis, reduced glomerular filtration rate (GFR), bone demineralization, and growth failure. Treatment focuses on correcting the acid-base imbalance through alkali supplementation (potassium, sodium, or magnesium bicarbonate or citrate) to reduce renal disease progression and promote normal growth and mineralization. Traditional treatments (alkali and potassium supplementation) often suffer from poor adherence due to frequent day and night administrations, gastrointestinal discomfort, and unpleasant taste. A novel investigational drug, ADV7103, which contains potassium citrate and potassium bicarbonate in an extended-release formulation, has recently been approved by the European Medicine Agency (EMA) for dRTA. Recent studies support its use as a first-line treatment, given its efficacy and safety profile.

Analysis of risk factors and development of a nomogram prediction model for renal tubular acidosis in primary Sjogren syndrome patients

OBJECTIVE

To investigate the risk factors of renal tubular acidosis (RTA) in patients with primary Sjögren's syndrome (pSS) and create a personalized nomogram for predicting pSS-RTA patients.

METHOD

Data from 99 pSS patients who underwent inpatient treatment at our hospital from January 2012 to January 2024 were retrospectively collected and analyzed. Bootstrap resampling technique, single-factor, and multi-factor logistic regression analyses were used to explore the risk factors for pSS-RTA. A nomogram was developed based on the results of the multivariate logistic model. The model was evaluated through receiver operating characteristic curve, C-index, calibration curve, and decision curve analysis. In addition, we graded the severity of pSS-RTA patients and used univariate analysis to assess the relationship between pSS-RTA severity and risk factors.

RESULTS

A multivariate logistic regression analysis revealed that concurrent thyroid disease, long symptom duration, subjective dry mouth, and positive RF were independent risk factors for pSS-RTA patients. Based on them, a personalized nomogram predictive model was established. With a p-value of 0.657 from the Hosmer-Lemeshow test, the model demonstrated a good fit. The AUC values in the training and validation groups were 0.912 and 0.896, indicating a strong discriminative power of the nomogram. The calibration curves for the training and validation groups closely followed the diagonal line with a slope of 1, confirming the model's reliable predictive ability. Furthermore, the decision curve analysis showed that the nomogram model had a net benefit in predicting pSS-RTA, emphasizing its clinical value.This study did not find an association between the severity of pSS-RTA and risk factors.

DISCUSSION

We developed a nomogram to predict RTA occurrence in pSS patients, and it is believed to provide a foundation for early identification and intervention for high-risk pSS patients.

Primary Distal Renal Tubular Acidosis: Toward an Optimal Correction of Metabolic Acidosis

The term classic, type 1 renal tubular acidosis or primary distal renal tubular acidosis is used to designate patients with impaired ability to excrete acid normally in the urine as a result of tubular transport defects involving type A intercalated cells in the collecting duct. The clinical phenotype is largely characterized by the complications of chronic metabolic acidosis (MA): stunted growth, bone abnormalities, and nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria and hypocitraturia. All these manifestations are preventable with early and sustained correction of MA with alkali therapy. The optimal target for plasma bicarbonate should be as close as possible to the range considered normal by current standards (between 23 and 28 mEq/L.). Most of the benefits of alkali therapy are tangible early in the course of the disease in childhood, but life-long treatment is required to prevent the vast array of complications attributable to chronic MA.

SGLT2 Inhibitor Use for Treatment of Hypocitraturia in a Distal Renal Tubular Acidosis

5-Amino salicylic acid (5-ASA) is a known culprit for the development of tubulointerstitial nephritis. Together with impaired kidney function, tubulointerstitial nephritis can lead to specific tubular malfunctions including distal renal tubular acidosis. Distal renal tubular acidosis is an acid-base disorder in which acid secretion in the distal part of the renal tubular system is decreased. Patients with distal renal tubular acidosis are predisposed to recurrently form calcium phosphate kidney stones. This results from the inability to acidify the urine properly as well as from a decreased citrate concentration in the urine, which is another pathognomonic feature of distal renal tubular acidosis. We present the case of a man in his late 40s with Crohn's disease who developed tubulointerstitial nephritis associated with 5-ASA leading to the development of distal renal tubular acidosis and recurrent calcium phosphate nephrolithiasis. After steroid therapy and partial recovery of kidney function, we observed an increase of citraturia in response to treatment with dapagliflozin, potentially indicating beneficial effects of sodium/glucose cotransporter 2 inhibition on the recurrence of calcium phosphate stone disease in interstitial nephritis-induced distal tubular acidosis.

Medullary Sponge Kidney and Its Relationship with Primary Distal Renal Tubular Acidosis: Case Reports and a Comprehensive Genetics-First Approach

Medullary sponge kidney (MSK) is a description of radiographic features. However, the pathogenesis of MSK remains unclear. MSK is supposed to be the cause of secondary distal renal tubular acidosis (dRTA), although there are case reports suggesting that MSK is a complication of primary dRTA. In addition to these reports, we report 3 patients with metabolic acidosis and MSK, in whom primary dRTA is confirmed by molecular genetic analyses of SLC4A1 and ATP6V1B1 genes. With a comprehensive genetics-first approach using the 100,000 Genomes Rare Diseases Project dataset, the association between MSK and primary dRTA is examined. We showed that many patients with MSK phenotypes are genetically tested with a gene panel which does not contain dRTA-associated genes, revealing opportunities for missed genetic diagnosis. Our cases highlight that the radiological description of MSK is not a straightforward disease or clinical phenotype. Therefore, when an MSK appearance is noted, a broader set of causes should be considered including genetic causes of primary dRTA as the underlying reason for medullary imaging abnormalities.

Nephrolithiasis and/or nephrocalcinosis is significantly related to renal dysfunction in patients with primary Sjögren's syndrome

OBJECTIVE

The present study compared the clinical features of patients with primary Sjögren's syndrome (pSS) with and without nephrolithiasis and/or nephrocalcinosis to determine factors related to renal dysfunction.

METHODS

The clinical features of 68 patients with anti-Sjogren's syndrome antigen A (SSA)/Ro-antibody-positive pSS with and without nephrolithiasis and/or nephrocalcinosis who underwent abdominal computed tomography and/or ultrasonography were retrospectively analysed.

RESULTS

Of the 68 patients with anti-SSA-antibody-positive pSS, 23 (33%) had renal nephrolithiasis and/or nephrocalcinosis, whereas 45 (67%) did not. Fourteen (20%) patients had renal dysfunction at diagnostic imaging. Among five patients who underwent renal biopsy, four patients with renal nephrolithiasis and/or nephrocalcinosis were diagnosed with tubulointerstitial nephritis, and one without nephrolithiasis and/or nephrocalcinosis was diagnosed with minimal change nephrotic syndrome. Estimated glomerular filtration rate at diagnostic imaging was significantly lower in patients with than without nephrolithiasis and/or nephrocalcinosis group (P = 0.010). In addition to nephrolithiasis and/or nephrocalcinosis (odds ratio [OR], 3.467; P = 0.045), the gap between serum sodium and chloride concentrations (OR, 10.400; P = 0.012) and increased urinary β2-microglobulin (OR, 5.444; P = 0.033) were associated with renal dysfunction at the time of diagnostic imaging.

CONCLUSION

Nephrolithiasis and/or nephrocalcinosis, normal anion gap metabolic acidosis, and tubulointerstitial damage are associated with renal dysfunction in patients with pSS.

Renal calcification in children with renal tubular acidosis: What a paediatrician ‎should ‎know‎

Renal tubular acidosis (RTA) can lead to renal calcification in children, which can cause various complications and impair renal function. This review provides pediatricians with a comprehensive understanding of the relationship between RTA and renal calcification, highlighting essential aspects for clinical management. The article analyzed relevant studies to explore the prevalence, risk factors, underlying mechanisms, and clinical implications of renal calcification in children with RTA. Results show that distal RTA (type 1) is particularly associated with nephrocalcinosis, which presents a higher risk of renal calcification. However, there are limitations to the existing literature, including a small number of studies, heterogeneity in methodologies, and potential publication bias. Longitudinal data and control groups are also lacking, which limits our understanding of long-term outcomes and optimal management strategies for children with RTA and renal calcification. Pediatricians play a crucial role in the early diagnosis and management of RTA to mitigate the risk of renal calcification and associated complications. In addition, alkaline therapy remains a cornerstone in the treatment of RTA, aimed at correcting the acid-base imbalance and reducing the formation of kidney stones. Therefore, early diagnosis and appropriate therapeutic interventions are paramount in preventing and managing renal calcification to preserve renal function and improve long-term outcomes for affected children. Further research with larger sample sizes and rigorous methodologies is needed to optimize the clinical approach to renal calcification in the context of RTA in the pediatric population.

2022 Recommendations of the AFU Lithiasis Committee: Medical management - from diagnosis to treatment

The morphological-compositional analysis of urinary stones allows distinguishing schematically several situations: dietary, digestive, metabolic/hormonal, infectious and genetic problems. Blood and urine testing are recommended in the first instance to identify risk factors of urinary stone disease in order to avoid recurrence or progression. The other objective is to detect a potential underlying pathology associated with high risk of urinary stone disease (e.g. primary hyperparathyroidism, primary or enteric hyperoxaluria, cystinuria, distal renal tubular acidosis) that may require specific management. Lifestyle-diet measures are the basis of the management of all stone types, but pharmacological treatments may be required. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendation (CPR) method and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis) [EAU 2022] and their adaptability to the French context.

The pathophysiology of distal renal tubular acidosis

The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease.

A Clinical Workflow for Cost-Saving High-Rate Diagnosis of Genetic Kidney Diseases

SIGNIFICANCE STATEMENT

To optimize the diagnosis of genetic kidney disorders in a cost-effective manner, we developed a workflow based on referral criteria for in-person evaluation at a tertiary center, whole-exome sequencing, reverse phenotyping, and multidisciplinary board analysis. This workflow reached a diagnostic rate of 67%, with 48% confirming and 19% modifying the suspected clinical diagnosis. We obtained a genetic diagnosis in 64% of children and 70% of adults. A modeled cost analysis demonstrated that early genetic testing saves 20% of costs per patient. Real cost analysis on a representative sample of 66 patients demonstrated an actual cost reduction of 41%. This workflow demonstrates feasibility, performance, and economic effect for the diagnosis of genetic kidney diseases in a real-world setting.

BACKGROUND

Whole-exome sequencing (WES) increases the diagnostic rate of genetic kidney disorders, but accessibility, interpretation of results, and costs limit use in daily practice.

METHODS

Univariable analysis of a historical cohort of 392 patients who underwent WES for kidney diseases showed that resistance to treatments, familial history of kidney disease, extrarenal involvement, congenital abnormalities of the kidney and urinary tract and CKD stage ≥G2, two or more cysts per kidney on ultrasound, persistent hyperechoic kidneys or nephrocalcinosis on ultrasound, and persistent metabolic abnormalities were most predictive for genetic diagnosis. We prospectively applied these criteria to select patients in a network of nephrology centers, followed by centralized genetic diagnosis by WES, reverse phenotyping, and multidisciplinary board discussion.

RESULTS

We applied this multistep workflow to 476 patients with eight clinical categories (podocytopathies, collagenopathies, CKD of unknown origin, tubulopathies, ciliopathies, congenital anomalies of the kidney and urinary tract, syndromic CKD, metabolic kidney disorders), obtaining genetic diagnosis for 319 of 476 patients (67.0%) (95% in 21 patients with disease onset during the fetal period or at birth, 64% in 298 pediatric patients, and 70% in 156 adult patients). The suspected clinical diagnosis was confirmed in 48% of the 476 patients and modified in 19%. A modeled cost analysis showed that application of this workflow saved 20% of costs per patient when performed at the beginning of the diagnostic process. Real cost analysis of 66 patients randomly selected from all categories showed actual cost reduction of 41%.

CONCLUSIONS

A diagnostic workflow for genetic kidney diseases that includes WES is cost-saving, especially if implemented early, and is feasible in a real-world setting.

Long-term complications of primary distal renal tubular acidosis

The clinical manifestations of primary distal renal tubular acidosis usually begin in childhood, but the disease is caused by a genetic defect that persists throughout life. This review focuses on the complications of distal tubular acidosis that occur or remain long-term such as nephrocalcinosis and urolithiasis, growth impairment, bone mineralization, severe hypokalemia, kidney cysts, and progressive kidney failure, as well as other persistent manifestations that occur independent of acidosis but are associated with some inherited forms of the disease. The pathogenic factors responsible for kidney failure are discussed in particular because it is a complication to which different publications have recently drawn attention and which affects a high percentage of adults with primary distal renal tubular acidosis. The need to maintain optimal metabolic control of the disease and scheduled clinical follow-up throughout life and the importance of organizing protocols for the transition of patients to adult nephrology services are emphasized.

A clinical approach to tubulopathies in children and young adults

Kidney tubules are responsible for the preservation of fluid, electrolyte and acid-base homeostasis via passive and active mechanisms. These physiological processes can be disrupted by inherited or acquired aetiologies. The net result is a tubulopathy. It is important to make a prompt and accurate diagnosis of tubulopathies in children and young adults. This allows timely and appropriate management, including disease-specific therapies, and avoids complications such as growth failure. Tubulopathies can present with a variety of non-specific clinical features which can be diagnostically challenging. In this review, we build from this common anatomical and physiological understanding to present a tangible appreciation of tubulopathies as they are likely to be clinically encountered among affected children and young adults.

Renal tubular acidosis and associated factors in patients with primary Sjögren's syndrome: a registry-based study

OBJECTIVES

To investigate the clinical features and factors associated with primary Sjögren's syndrome (pSS)-associated renal tubular acidosis (RTA).

METHOD

This case-control study was based on a multicenter pSS registry established by the Chinese Rheumatism Data Center. Patients with pSS, including those with RTA and those without renal involvement, between May 2016 and March 2020 were included in the analysis. Demographic, clinical, and laboratory data were also collected. Univariate and multivariate logistic regression analyses were used to identify factors that were associated with pSS-RTA.

RESULTS

This study included 257 pSS patients with RTA and 4222 patients without renal involvement. Significantly younger age at disease onset (40.1 ± 14.1 vs. 46.2 ± 13.1 years, P < 0.001), longer diagnosis interval (15.0 interquartile range [IQR] [1.0, 48.0] vs. 6.0 IQR [0, 34.0] months, P < 0.001), higher EULAR Sjögren's syndrome disease activity index (9 IQR [5, 15] vs. 3 IQR [0, 8], P < 0.001), and a higher prevalence of decreased estimated glomerular filtration rate (25.0% vs. 6.6%, P < 0.001) were observed in pSS patients with RTA than in those without renal involvement. Factors that were independently associated with pSS-RTA included age at disease onset ≤ 35 years (odds ratio [OR] 3.00, 95% confidence interval [CI] 2.27-3.97), thyroid disorders (OR 1.49, 95% CI 1.04-2.14), subjective dry mouth (OR 3.29, 95% CI 1.71-6.35), arthritis (OR 1.57, 95% CI 1.10-2.25), anti-SSB antibody positivity (OR 1.80, 95% CI 1.33-2.45), anemia (OR 1.67, 95% CI 1.26-2.21), elevated alkaline phosphatase level (OR 2.14, 95% CI 1.26-3.65), decreased albumin level (OR 1.61, 95% CI 1.00-2.60), and elevated erythrocyte sedimentation rate (OR 1.78, 95% CI 1.16-2.73).

CONCLUSIONS

Delayed diagnosis and decreased kidney function are common in pSS patients with RTA. pSS should be considered in patients with RTA, and early recognition and treatment may be useful in slowing the deterioration of renal function in patients with pSS-RTA. Key Points • pSS patients with RTA have earlier disease onset and higher disease activity than pSS patients without RTA, but the diagnosis was frequently delayed. • Decreased kidney function are common in pSS patients with RTA. • Sjögren's syndrome should be considered in young female patients with unexplained RTA, whereas RTA should be screened in pSS patients with early disease onset and elevated ALP level.

Assessment of Kidney Function in Children

A good understanding of kidney function tests is essential for patient care. Urinalysis is the commonest used test for screening purposes in ambulatory settings. Glomerular function is assessed further by urine protein excretion and estimated glomerular filtration rate and tubular function by various tests such as urine anion gap and excretion of sodium, calcium, and phosphate. In addition, kidney biopsy and/or genetic analyses may be required to further characterize the underlying kidney disease. In this article, we discuss maturation and the assessment of kidney function in children.

Whole-exome sequencing and variant spectrum in children with suspected inherited renal tubular disorder: the East India Tubulopathy Gene Study

BACKGROUND

Inherited tubulopathies are a heterogeneous group of genetic disorders making whole-exome sequencing (WES) the preferred diagnostic methodology.

METHODS

This was a multicenter descriptive study wherein children (< 18 years) with clinically suspected tubular disorders were recruited for molecular testing through WES. Multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing were done when required. Variants were classified as per American College of Medical Genetics 2015 guidelines and pathogenic (P)/likely pathogenic (LP) variants were considered causative.

RESULTS

There were 77 index cases (male =73%). Median age at diagnosis was 48 months (IQR 18.5 to 108 months). At recruitment, the number of children in each clinical group was as follows: distal renal tubular acidosis (dRTA) = 25; Bartter syndrome = 18; isolated hypophosphatemic rickets (HP) = 6; proximal tubular dysfunction (pTD) = 12; nephrogenic diabetes insipidus (NDI) = 6; kidney stone/nephrocalcinosis (NC) = 6; others = 4. We detected 55 (24 novel) P/LP variants, providing genetic diagnoses in 54 children (70%). The diagnostic yield of WES was highest for NDI (100%), followed by HP (83%; all X-linked HP), Bartter syndrome (78%), pTD (75%), dRTA (64%), and NC (33%). Molecular testing had a definite impact on clinical management in 24 (31%) children. This included revising clinical diagnosis among 14 children (26% of those with a confirmed genetic diagnosis and 18% of the overall cohort), detection of previously unrecognized co-morbidities among 8 children (sensorineural deafness n = 5, hemolytic anemia n = 2, and dental changes n = 1) and facilitating specific medical treatment for 7 children (primary hyperoxaluria n = 1, cystinosis n = 4, tyrosinemia n = 2).

CONCLUSION

WES is a powerful tool in the diagnosis and management of children with inherited tubulopathies in the Indian population. A higher resolution version of the Graphical abstract is available as Supplementary information.

Young Adults With Hereditary Tubular Diseases: Practical Aspects for Adult-Focused Colleagues

Recent advances in the management of kidney tubular diseases have resulted in a significant cohort of adolescents and young adults transitioning from pediatric- to adult-focused care. Most of the patients under adult-focused care have glomerular diseases, whereas rarer tubular diseases form a considerable proportion of pediatric patients. The purpose of this review is to highlight the clinical signs and symptoms of tubular disorders, as well as their diagnostic workup, including laboratory findings and imaging, during young adulthood. We will then discuss more common disorders such as cystinosis, cystinuria, distal kidney tubular acidosis, congenital nephrogenic diabetes insipidus, Dent disease, rickets, hypercalciuria, and syndromes such as Bartter, Fanconi, Gitelman, Liddle, and Lowe. This review is a practical guide on the diagnostic and therapeutic approach of tubular conditions affecting young adults who are transitioning to adult-focused care.

Ibuprofen-Associated Hypokalemia and Metabolic Acidosis: Systematic Literature Review

OBJECTIVE

Ibuprofen is a widely used nonsteroidal anti-inflammatory drug, which has been occasionally associated with hypokalemia and metabolic acidosis. The objective of this report is to analyze the literature on this issue and to address the underlying pathophysiology.

DATA SOURCES

Excerpta Medica, the National Library of Medicine, and Web of Science were searched from inception to July 16, 2021.

STUDY SELECTION AND DATA EXTRACTION

Papers reporting individually documented humans on ibuprofen with hypokalemia, acidosis, or both were retained. Data were extracted using a checklist.

DATA SYNTHESIS

For the final analysis, we evaluated 41 reports describing 50 cases (26 males and 24 females; 36 adults and 14 children) with often profound hypokalemia, acidosis, or both after ingestion of ibuprofen. Twenty-six cases were acute and 24 long term. Hypokalemia and acidosis occurred not only after ingestion of very high doses but also after ingestion of moderately high or even normal doses of ibuprofen. Laboratory values consistent with an excessive urinary potassium excretion or an altered urinary acidification were often disclosed in most cases. Discontinuation of ibuprofen resulted in a resolution of hypokalemia and acidosis within days in 47 cases. The course was lethal in 3 cases.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review highlights potentially fatal side effects of ibuprofen and can help doctors who are confronted with such a situation.

CONCLUSIONS

These data highlight the potential of ibuprofen to occasionally induce hypokalemia and acidosis of renal origin. Discontinuation of ibuprofen results in a resolution within days.

Evaluation of urinary acidification in children: Clinical utility

The kidney plays a fundamental role in acid-base homeostasis by reabsorbing the filtered bicarbonate and by generating new bicarbonate, to replace that consumed in the buffering of non-volatile acids, a process that leads to the acidification of urine and the excretion of ammonium (NH₄ ⁺). Therefore, urine pH (UpH) and urinary NH₄ ⁺ (UNH₄ ⁺) are valuable parameters to assess urinary acidification. The adaptation of automated plasma NH₄ ⁺ quantification methods to measure UNH₄ ⁺ has proven to be an accurate and feasible technique, with diverse potential indications in clinical practice. Recently, reference values for spot urine NH₄ ⁺/creatinine ratio in children have been published. UpH and UNH₄ ⁺, aside from their classical application in the study of metabolic acidosis, have shown to be useful in the identification of incomplete distal renal tubular acidosis (dRTA), an acidification disorder, without overt metabolic acidosis, extensively described in adults, and barely known in children, in whom it has been found to be associated to hypocitraturia, congenital kidney abnormalities and growth impairment. In addition, a low UNH₄ ⁺ in chronic kidney disease (CKD) is a risk factor for glomerular filtration decay and mortality in adults, even in the absence of overt metabolic acidosis. We here emphasize on the need of measuring UpH and UNH₄ ⁺ in pediatric population, establishing reference values, as well as exploring their application in metabolic acidosis, CKD and disorders associated with incomplete dRTA, including growth retardation of unknown cause.