Molecular aspects and long-term outcome of patients with primary distal renal tubular acidosis

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.

Genetic variants affecting mitochondrial function provide further insights for kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a complex disorder that has become a high prevalence global health problem, with diabetes being its predominant pathophysiologic driver. Autosomal genetic variation only explains some of the predisposition to kidney disease. Variations in the mitochondrial genome (mtDNA) and nuclear-encoded mitochondrial genes (NEMG) are implicated in susceptibility to kidney disease and CKD progression, but they have not been thoroughly explored. Our aim was to investigate the association of variation in both mtDNA and NEMG with CKD (and related traits), with a particular focus on diabetes.

METHODS

We used the UK Biobank (UKB) and UK-ROI, an independent collection of individuals with type 1 diabetes mellitus (T1DM) patients.

RESULTS

Fourteen mitochondrial variants were associated with estimated glomerular filtration rate (eGFR) in UKB. Mitochondrial variants and haplogroups U, H and J were associated with eGFR and serum variables. Mitochondrial haplogroup H was associated with all the serum variables regardless of the presence of diabetes. Mitochondrial haplogroup X was associated with end-stage kidney disease (ESKD) in UKB. We confirmed the influence of several known NEMG on kidney disease and function and found novel associations for SLC39A13, CFL1, ACP2 or ATP5G1 with serum variables and kidney damage, and for SLC4A1, NUP210 and MYH14 with ESKD. The G allele of TBC1D32-rs113987180 was associated with higher risk of ESKD in patients with diabetes (OR:9.879; CI95%:4.440-21.980; P = 2.0E-08). In UK-ROI, AGXT2-rs71615838 and SURF1-rs183853102 were associated with diabetic nephropathies, and TFB1M-rs869120 with eGFR.

CONCLUSIONS

We identified novel variants both in mtDNA and NEMG which may explain some of the missing heritability for CKD and kidney phenotypes. We confirmed the role of MT-ND5 and mitochondrial haplogroup H on renal disease (serum variables), and identified the MT-ND5-rs41535848G variant, along with mitochondrial haplogroup X, associated with higher risk of ESKD. Despite most of the associations were independent of diabetes, we also showed potential roles for NEMG in T1DM.

Pediatric renal lithiasis in Spain: research, diagnostic and therapeutic challenges, and perspectives

Incidence and prevalence of urolithiasis is apparently increasing worldwide, also among children and adolescents. Nevertheless, robust data have only been obtained in a few countries. In Spain, a voluntary Registry for Pediatric Renal Lithiasis has been active since 2015. Irregular participation limits its applicability, as well as its limitation to patients with a stone available for morphocompositional study, to obtain data about incidence and prevalence. On the other hand, findings about typology of stones and clinical and analytical characteristics of these subjects have been communicated in several meetings. Other valuable efforts in this field are the elaboration of guidelines for the collection and processing of urine samples for the study of urolithiasis in pediatric patients with the consensus of the Spanish Society for Pediatric Nephrology (AENP) as well as the Spanish Society for Laboratory Medicine (SEQC), the collaborative network RenalTube for the diagnosis of primary tubulopathies and the registry of patients with Primary Hyperoxaluria (OxalSpain). In many hospitals from the public healthcare system, pediatric nephrologists are the specialists in charge of the management of children with kidney stones, but there is no formal regulation on this competence. Other specialists, such as urologists, pediatric surgeons or pediatric urologists, in many cases do not offer a complete insight into the etiopathogenic mechanisms and the consequent medical treatment. Access to medication according to standards of treatment is warranted, provided a correct diagnosis is achieved, but criteria for the reimbursement of certain therapies, such as RNAi drugs for primary hyperoxaluria, are arguable.

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.

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.

Distal renal tubular acidosis presenting with an acute hypokalemic paralysis in an older child with severe vesicoureteral reflux and syringomyelia: a case report

Background

Distal renal tubular acidosis (dRTA) is the most common type of renal tubular acidosis (RTA) in children. Pediatric dRTA is usually genetic and rarely occurs due to acquired issues such as obstructive uropathies, recurrent urinary tract infections (UTIs), and chronic kidney disease (CKD). Although persistent hypokalemia frequently occurs with dRTA, acute hypokalemic paralysis is not frequently reported, especially in older children.

Case presentation

An eight-year-old girl presented with an acute first episode of paralysis. A physical examination revealed normal vital signs, short stature consistent with her genetic potential, and decreased muscle strength of her upper and lower extremities. Preexisting conditions included stage 4 CKD due to recurrent UTIs, severe vesicoureteral reflux and bilateral hydronephrosis, neurogenic bladder, and multisegment thoracic syringomyelia. Her laboratory work-up revealed hypokalemic, hyperchloremic metabolic acidosis with a normal anion gap. She also had a urine osmolal gap of 1.9 mOsmol/kg with a high urine pH. Intravenous potassium replacement resulted in a complete resolution of her paralysis. She was diagnosed with dRTA and discharged with oral bicarbonate and slow-release potassium supplementation.

Conclusions

This case report highlights the importance of considering dRTA in the differential diagnosis of hypokalemic acute paralysis in children. Additionally, in children with neurogenic lower urinary tract dysfunction and recurrent UTIs, early diagnosis of spinal cord etiology is crucial to treat promptly, slow the progression of CKD, and prevent long-term complications such as RTA.

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.