Improving outcomes for patients with distal renal tubular acidosis: recent advances and challenges ahead

Monogenic features of urolithiasis: A comprehensive review

Objective

Urolithiasis formation has been attributed to environmental and dietary factors. However, evidence is accumulating that genetic background can contribute to urolithiasis formation. Advancements in the identification of monogenic causes using high-throughput sequencing technologies have shown that urolithiasis has a strong heritable component.

Methods

This review describes monogenic factors implicated in a genetic predisposition to urolithiasis. Peer-reviewed journals were evaluated by a PubMed search until July 2023 to summarize disorders associated with monogenic traits, and discuss clinical implications of identification of patients genetically susceptible to urolithiasis formation.

Results

Given that more than 80% of urolithiases cases are associated with calcium accumulation, studies have focused mainly on monogenetic contributors to hypercalciuric urolithiases, leading to the identification of receptors, channels, and transporters involved in the regulation of calcium renal tubular reabsorption. Nevertheless, available candidate genes and linkage methods have a low resolution for evaluation of the effects of genetic components versus those of environmental, dietary, and hormonal factors, and genotypes remain undetermined in the majority of urolithiasis formers.

Conclusion

The pathophysiology underlying urolithiasis formation is complex and multifactorial, but evidence strongly suggests the existence of numerous monogenic causes of urolithiasis in humans.

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.

Genetic Diagnosis and Treatment of Inherited Renal Tubular Acidosis

Background

Renal tubular acidosis (RTA) is caused by various disruptions to the secretion of H+ by distal renal tubules and/or dysfunctional reabsorption of HCO3- by proximal renal tubules, which causes renal acidification dysfunction, ultimately leading to a clinical syndrome characterized by hyperchloremic metabolic acidosis with a normal anion gap. With the development of molecular genetics and gene sequencing technology, inherited RTA has also attracted attention, and an increasing number of RTA-related pathogenic genes have been discovered and reported.

Summary

This paper focuses on the latest progress in the research of inherited RTA and systematically reviews the pathogenic genes, protein functions, clinical manifestations, internal relationship between genotypes and clinical phenotypes, diagnostic clues, differential diagnosis, and treatment strategies associated with inherited RTA. This paper aims to deepen the understanding of inherited RTA and reduce the missed diagnosis and misdiagnosis of RTA.

Key Messages

This review systematically summarizes the pathogenic genes, pathophysiological mechanisms, differential diagnosis, and treatment of different types of inherited RTA, which has good clinical value for guiding the diagnosis and treatment of inherited RTA.

Research progress on renal calculus associate with inborn error of metabolism

Renal calculus is a common disease with complex etiology and high recurrence rate. Recent studies have revealed that gene mutations may lead to metabolic defects which are associated with the formation of renal calculus, and single gene mutation is involved in relative high proportion of renal calculus. Gene mutations cause changes in enzyme function, metabolic pathway, ion transport, and receptor sensitivity, causing defects in oxalic acid metabolism, cystine metabolism, calcium ion metabolism, or purine metabolism, which may lead to the formation of renal calculus. The hereditary conditions associated with renal calculus include primary hyperoxaluria, cystinuria, Dent disease, familial hypomagnesemia with hypercalciuria and nephrocalcinosis, Bartter syndrome, primary distal renal tubular acidosis, infant hypercalcemia, hereditary hypophosphatemic rickets with hypercalciuria, adenine phosphoribosyltransferase deficiency, hypoxanthine-guanine phosphoribosyltransferase deficiency, and hereditary xanthinuria. This article reviews the research progress on renal calculus associated with inborn error of metabolism, to provide reference for early screening, diagnosis, treatment, prevention and recurrence of renal calculus.

Mutations and clinical characteristics of dRTA caused by SLC4A1 mutations: Analysis based on published patients

BACKGROUND AND AIMS

The genetic and clinical characteristics of patients with distal renal tubular acidosis (dRTA) caused by SLC4A1 mutations have not been systematically recorded before. Here, we summarized the SLC4A1 mutations and clinical characteristics associated with dRTA.

METHODS

Database was searched, and the mutations and clinical manifestations of patients were summarized from the relevant articles.

RESULTS

Fifty-three eligible articles involving 169 patients were included and 41 mutations were identified totally. Fifteen mutations involving 100 patients were autosomal dominant inheritance, 21 mutations involving 61 patients were autosomal recessive inheritance. Nephrocalcinosis or kidney stones were found in 72.27%, impairment in renal function in 14.29%, developmental disorders in 61.16%, hematological abnormalities in 33.88%, and muscle weakness in 13.45% of patients. The age of onset was younger (P < 0.01), urine pH was higher (P < 0.01), and serum potassium was lower (P < 0.001) in recessive patients than patients with dominant SLC4A1 mutations. Autosomal recessive inheritance was more often found in Asian patients (P < 0.05).

CONCLUSIONS

The children present with metabolic acidosis with high urinary pH, accompanying hypokalemia, hyperchloremia, nephrocalcinosis, growth retardation and hematological abnormalities should be suspected as dRTA and suggested a genetic testing. The patients with recessive dRTA are generally more severely affected than that with dominant SLC4A1 mutations. Autosomal recessive inheritance was more often found in Asian patients, and more attentions should be paid to the Asian patients.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

Single-Cell Gene Expression Analysis in Patients with Medullary Sponge Kidney and a Retrospective Study

OBJECTIVE

To establish better diagnosis thinking and provide advanced understanding of MSK, the CT imaging features, clinical characteristics, and the expression of suspected genes in the kidney spatiotemporal immune zonation and fetal renal development were investigated.

METHODS

17 patients with MSK hospitalized in our hospital were selected as our research subjects. Human Phenotype Ontology, MalaCards: The Human Disease Database, GeneCards: The Human Gene Database, Human Protein Atlas, and Single Cell Expression Atlas were used to analyze this disease.

RESULTS

In our 17 patients, the incidence of MSK tended to be the same in male and female, and the onset age of MSK was probably 31-50 years old. The top one related disease of MSK was nephrocalcinosis and the most frequent phenotype related to MSK was nephrolithiasis. In addition, the expression of HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 has been implicated in both human kidney immune zonation and fetal kidney development.

CONCLUSIONS

HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 could be independent indicators for the diagnosis and preventive intervention of MSK patients, and abnormal kidney development due to mutations in key genes was the underlying cause of MSK.

Cell Physiology and Molecular Mechanism of Anion Transport by Erythrocyte Band 3/AE1

The major transmembrane protein of the red blood cell, known as band 3, AE1, and SLC4A1, has two main functions: 1) catalysis of Cl^-/HCO₃^- exchange, one of the steps in CO₂ excretion; 2) anchoring the membrane skeleton. This review summarizes the 150 year history of research on red cell anion transport and band 3 as an experimental system for studying membrane protein structure and ion transport mechanisms. Important early findings were that red cell Cl^- transport is a tightly coupled 1:1 exchange and band 3 is labeled by stilbenesulfonate derivatives that inhibit anion transport. Biochemical studies showed that the protein is dimeric or tetrameric (paired dimers) and that there is one stilbenedisulfonate binding site per subunit of the dimer. Transport kinetics and inhibitor characteristics supported the idea that the transporter acts by an alternating access mechanism with intrinsic asymmetry. The sequence of band 3 cDNA provided a framework for detailed study of protein topology and amino acid residues important for transport. The identification of genetic variants produced insights into the roles of band 3 in red cell abnormalities and distal renal tubular acidosis. The publication of the membrane domain crystal structure made it possible to propose concrete molecular models of transport. Future research directions include improving our understanding of the transport mechanism at the molecular level and of the integrative relationships among band 3, hemoglobin, carbonic anhydrase, and gradients (both transmembrane and subcellular) of HCO₃^-, Cl^-, O₂, CO₂, pH, and NO metabolites during pulmonary and systemic capillary gas exchange.

Distal Renal Tubular Acidosis in an Iranian Patient with Hereditary Spherocytosis

Background:

Hereditary spherocytosis and hereditary dRTA are associated with mutations in the SLC4A1 gene encoding the AE1. In this study, some patients with clinical evidence of congenital HS and renal symptoms were investigated.

Methods:

Twelve patients with congenital HS and renal symptoms were recruited from Ali-Asghar Children’s Hospital (Tehran, Iran). A patient suspected of having dRTA was examined using WES method, followed by Sanger sequencing.

Results:

One patient (HS03) showed severe failure to thrive, short stature, frequent urinary infection, and weakness. A homozygote (rs571376371 for c.2494C>T; p.Arg832Cys) and a heterozygote (rs377051298 for c.466C>T; p.Arg156Trp) missense variant were identified in the SLC4A1 and SPTA1 genes, respectively. The compound heterozygous mutations manifested as idRTA and severe HS in patient HS03.

Conclusion:

Our observations, for the first time, revealed clinical and genetic characteristics of idRTA and severe HS in an Iranian patient HS03.

Hereditary distal renal tubular acidosis: Genotypic correlation, evolution to long term, and new therapeutic perspectives

Distal renal tubular acidosis (DRTA) is a rare disease resulting from a failure in the normal urine acidification process at the distal tubule and collecting duct level. It is characterised by persistent hyperchloremic metabolic acidosis, with a normal anion gap in plasma, in the presence of high urinary pH and low urinary excretion of ammonium. To date, 5 genes whose mutations give rise to primary DRTA have been described. Alterations in the ATP6V1B1 and ATP6V0A4 genes are inherited recessively and are associated with forms of early onset and, in many cases, with neurosensorial deafness. Pathogenic variants in the SLC4A1 gene are habitually inherited dominantly and give rise to milder symptoms, with a later diagnosis and milder electrolytic alterations. Nonetheless, evolution to nephrocalcinosis and lithiasis, and the development of chronic kidney disease in the medium to long term has been described in a similar manner in all 3 groups. Lastly, recessive forms of DTRA associated to mutations in the FOXI1 and WDR72 genes have also been described. The clinical management of DTRA is based on bicarbonate or citrate salts, which do not succeed in correcting all cases of the metabolic alterations described and, thus, the consequences associated with them. Recently, a new treatment based on slow-release bicarbonate and citrate salts has received the designation of orphan drug in Europe for the treatment of DTRA.

Distal renal tubular acidosis: a systematic approach from diagnosis to treatment

Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO₃ is impaired, leading to chronic metabolic acidosis with normal anion gap. In the current review, the focus is placed on the most common type of RTA, Type 1 RTA or Distal RTA (dRTA), which is a rare chronic genetic disorder characterized by an inability of the distal nephron to secrete hydrogen ions in the presence of metabolic acidosis. Over the years, knowledge of the molecular mechanisms behind acid secretion has improved, thereby greatly helping the diagnosis of dRTA. The primary or inherited form of dRTA is mostly diagnosed in infancy, childhood, or young adulthood, while the acquired secondary form, as a consequence of other disorders or medications, can happen at any age, although it is more commonly seen in adults. dRTA is not as “benign” as previously assumed, and can have several, highly variable long-term consequences. The present review indeed reports and summarizes both clinical symptoms and diagnosis, long-term outcomes, genetic inheritance, epidemiology and current treatment options, with the aim of shedding more light onto this rare disorder. Being a chronic condition, dRTA also deserves attention in the transition between pediatric and adult nephrology care, and as a rare disease it has a place in the European and Italian rare nephrological diseases network.

Renal Tubular Acidosis and Management Strategies: A Narrative Review

Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid−base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.

Severe Hypokalemia Secondary to Transient Distal Renal Tubular Acidosis in a Previously Healthy Woman

Normal anion gap (non-gap) hyperchloremic acidosis with hypokalemia is a medical emergency. There are several causes of this metabolic phenomenon, of which distal renal tubular acidosis is among the very rare causes. In this report, we present an unusual case of a previously healthy woman who was admitted to the intensive care unit with a short history of severe muscle weakness. She had no significant past medical history and was not taking any regular medication. There was also no history of recent drug or herb ingestion. Investigations demonstrated a combination of severe hypokalemia, hyperchloremia, hypobicarbonatemia (non-gap metabolic acidosis), and relatively raised urinary potassium and urinary pH in the presence of severe hypokalemia and metabolic acidosis. Results suggested a diagnosis of distal renal tubular acidosis. The patient responded rapidly to a short course of electrolyte replacement therapy and the condition resolved spontaneously thereafter. This case highlights the fact that distal renal tubular acidosis can occur as a transient phenomenon in previously healthy individuals.

Safety, efficacy, and acceptability of ADV7103 during 24 months of treatment: an open-label study in pediatric and adult patients with distal renal tubular acidosis

BACKGROUND

A new prolonged-release formulation of potassium citrate and potassium bicarbonate, ADV7103, has been shown to improve metabolic control, palatability, and gastrointestinal safety in patients with distal renal tubular acidosis (dRTA) when compared to standard of care (SoC) treatments. The present work evaluates safety and efficacy of ADV7103 during 24 months.

METHODS

Thirty pediatric and adult patients were included in an open-label extension study after a phase II/III trial. Safety and tolerability were assessed. Plasma bicarbonate and potassium levels, as well as urine parameters, were evaluated over time. Acceptability, adherence, and quality of life were also assessed. The evolution of clinical consequences of dRTA in the cohort was explored.

RESULTS

There were 104 adverse events (AEs) reported, but only 9 gastrointestinal events observed in five patients (17%) were considered to be related to ADV7103 treatment. There were no AEs leading to treatment discontinuation. Plasma bicarbonate and potassium levels were in the normal ranges at the different visits, respectively, in 69-86% and 83-93% of patients. Overall adherence rates were ≥ 75% throughout the whole study in 79% patients. An average improvement of quality of life of 89% was reported at 24 months of study.

CONCLUSIONS

Common AEs concerned metabolism and gastrointestinal disorders; the former being related to the disease. Less than half of the gastrointestinal AEs were related to ADV7103 treatment and they were mostly mild in severity. Metabolic parameters were maintained in the normal ranges in most patients. Patient satisfaction was high and adherence to treatment was good and remained stable.

TRIAL REGISTRATION NUMBER

Registered as EudraCT 2013-003828-36 on the 3rd of September 2013.

Hereditary distal renal tubular acidosis: Genotypic correlation, evolution to long term, and new therapeutic perspectives

Distal renal tubular acidosis (DRTA) is a rare disease resulting from a failure in the normal urine acidification process at the distal tubule and collecting duct level. It is characterised by persistent hyperchloremic metabolic acidosis, with a normal anion gap in plasma, in the presence of high urinary pH and low urinary excretion of ammonium. To date, 5 genes whose mutations give rise to primary DRTA have been described. Alterations in the ATP6V1B1 and ATP6V0A4 genes are inherited recessively and are associated with forms of early onset and, in many cases, with neurosensorial deafness. Pathogenic variants in the SLC4A1 gene are habitually inherited dominantly and give rise to milder symptoms, with a later diagnosis and milder electrolytic alterations. Nonetheless, evolution to nephrocalcinosis and lithiasis, and the development of chronic kidney disease in the medium to long term has been described in a similar manner in all 3groups. Lastly, recessive forms of DTRA associated to mutations in the FOXI1 and WDR72 genes have also been described. The clinical management of DTRA is based on bicarbonate or citrate salts, which do not succeed in correcting all cases of the metabolic alterations described and, thus, the consequences associated with them. Recently, a new treatment based on slow-release bicarbonate and citrate salts has received the designation of orphan drug in Europe for the treatment of DTRA.

Renal Tubular Acidosis

Renal tubular acidosis (RTA) comprises a group of disorders characterized by low capacity for net acid excretion and persistent hyperchloremic metabolic acidosis, despite preserved glomerular filtration rate. RTA are classified into chiefly three types (1, 2 and 4) based on pathophysiology and clinical and laboratory characteristics. Most patients have primary RTA that presents in infancy with polyuria, growth retardation, rickets and/or hypotonia. Diagnosis requires careful evaluation, including exclusion of other entities that can cause acidosis. A variety of tests, administered stepwise, are useful for the diagnosis and characterization of RTA. A genetic or acquired basis can be determined in majority of patients through focused evaluation. Management involves correction of acidosis and dyselectrolytemia; patients with proximal RTA with Fanconi syndrome and rickets require additional supplements of phosphate and vitamin D.

Urinary Extracellular Vesicles and Salt-Losing Tubulopathies: A Proteomic Approach

Renal tubular cells release urinary extracellular vesicles (uEV) that are considered a promising source of molecular markers for renal dysfunction and injury. We investigated uEV proteomes of patients with hereditary salt-losing tubulopathies (SLTs), focusing on those caused by Gitelman and Bartter (BS) syndromes, to provide potential markers for differential diagnosis. Second morning urine was collected from patients with genetically proven SLTs and uEV were isolated by the ultracentrifugation-based protocol. The uEV proteome was run through a diagonal bidimensional electrophoresis (16BAC/SDS-PAGE), to improve hydrophobic protein resolution. Sixteen differential spots from the proteome of two variants (BS2 and BS3) were analysed by nLC-ESI-MS/MS after in-gel tryptic digestion. A total of 167 protein species were identified from 7 BS2 spots and 9 BS3 spot. Most of these proteins were membrane-associated proteins, in particular transmembrane proteins, and were related to typical renal functions. The differential content of some uEV was then validated by immunoblotting. Our work suggests that uEV proteomics represents a promising strategy for the identification of differential SLT proteins. This could play a role in understanding the pathophysiological disease mechanisms and may support the recognition of different syndromes.

Nephrocalcinosis: A Review of Monogenic Causes and Insights They Provide into This Heterogeneous Condition

The abnormal deposition of calcium within renal parenchyma, termed nephrocalcinosis, frequently occurs as a result of impaired renal calcium handling. It is closely associated with renal stone formation (nephrolithiasis) as elevated urinary calcium levels (hypercalciuria) are a key common pathological feature underlying these clinical presentations. Although monogenic causes of nephrocalcinosis and nephrolithiasis are rare, they account for a significant disease burden with many patients developing chronic or end-stage renal disease. Identifying underlying genetic mutations in hereditary cases of nephrocalcinosis has provided valuable insights into renal tubulopathies that include hypercalciuria within their varied phenotypes. Genotypes affecting other enzyme pathways, including vitamin D metabolism and hepatic glyoxylate metabolism, are also associated with nephrocalcinosis. As the availability of genetic testing becomes widespread, we cannot be imprecise in our approach to nephrocalcinosis. Monogenic causes of nephrocalcinosis account for a broad range of phenotypes. In cases such as Dent disease, supportive therapies are limited, and early renal replacement therapies are necessitated. In cases such as renal tubular acidosis, a good renal prognosis can be expected providing effective treatment is implemented. It is imperative we adopt a precision-medicine approach to ensure patients and their families receive prompt diagnosis, effective, tailored treatment and accurate prognostic information.

Role of Citrate in Pathophysiology and Medical Management of Bone Diseases

Citrate is an intermediate in the “Tricarboxylic Acid Cycle” and is used by all aerobic organisms to produce usable chemical energy. It is a derivative of citric acid, a weak organic acid which can be introduced with diet since it naturally exists in a variety of fruits and vegetables, and can be consumed as a dietary supplement. The close association between this compound and bone was pointed out for the first time by Dickens in 1941, who showed that approximately 90% of the citrate bulk of the human body resides in mineralised tissues. Since then, the number of published articles has increased exponentially, and considerable progress in understanding how citrate is involved in bone metabolism has been made. This review summarises current knowledge regarding the role of citrate in the pathophysiology and medical management of bone disorders.

Distal renal tubular acidosis: genetic causes and management

BACKGROUND

Distal renal tubular acidosis (dRTA) is a kidney tubulopathy that causes a state of normal anion gap metabolic acidosis due to impairment of urine acidification. This review aims to summarize the etiology, pathophysiology, clinical findings, diagnosis and therapeutic approach of dRTA, with emphasis on genetic causes of dRTA.

DATA SOURCES

Literature reviews and original research articles from databases, including PubMed and Google Scholar. Manual searching was performed to identify additional studies about dRTA.

RESULTS

dRTA is characterized as the dysfunction of the distal urinary acidification, leading to metabolic acidosis. In pediatric patients, the most frequent etiology of dRTA is the genetic alteration of genes responsible for the codification of distal tubule channels, whereas, in adult patients, dRTA is more commonly secondary to autoimmune diseases, use of medications and uropathies. Patients with dRTA exhibit failure to thrive and important laboratory alterations, which are used to define the diagnosis. The oral alkali and potassium supplementation can correct the biochemical defects, improve clinical manifestations and avoid nephrolithiasis and nephrocalcinosis.

CONCLUSIONS

dRTA is a multifactorial disease leading to several clinical manifestations. Clinical and laboratory alterations can be corrected by alkali replacement therapy.