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Progressive sensorineural hearing loss in association with distal renal tubular acidosis.

The autosomal recessive inherited syndrome of distal renal tubular acidosis and sensorineural hearing loss may present in one of two distinct fashions. The rare adolescent form is characterized by mild renal tubular acidosis, mild to moderate sensorineural hearing loss, and otherwise normal growth and development. The more common infantile type typically presents in the first year of life with failure to thrive, acidosis, and a more severe sensorineural hearing loss. In this report, progression of sensorineural hearing loss is documented for the first time in two siblings with the infantile variant. This association suggests that all children with distal renal tubular acidosis should undergo sequential audiologic evaluations with the institution of appropriate amplification and educational intervention as needed.

Acidosis, Renal Tubular↗

Proximal renal tubular acidosis in TASK2 K+ channel-deficient mice reveals a mechanism for stabilizing bicarbonate transport.

The acid- and volume-sensitive TASK2 K+ channel is strongly expressed in renal proximal tubules and papillary collecting ducts. This study was aimed at investigating the role of TASK2 in renal bicarbonate reabsorption by using the task2 -/- mouse as a model. After backcross to C57BL6, task2 -/- mice showed an increased perinatal mortality and, in adulthood, a reduced body weight and arterial blood pressure. Patch-clamp experiments on proximal tubular cells indicated that TASK2 was activated during HCO3- transport. In control inulin clearance measurements, task2 -/- mice showed normal NaCl and water excretion. During i.v. NaHCO3 perfusion, however, renal Na+ and water reabsorption capacity was reduced in -/- animals. In conscious task2 -/- mice, blood pH, HCO3- concentration, and systemic base excess were reduced but urinary pH and HCO3- were increased. These data suggest that task2 -/- mice exhibit metabolic acidosis caused by renal loss of HCO3-. Both in vitro and in vivo results demonstrate the specific coupling of TASK2 activity to HCO3- transport through external alkalinization. The consequences of the task2 gene inactivation in mice are reminiscent of the clinical manifestations seen in human proximal renal tubular acidosis syndrome.

Acidosis, Renal Tubular↗

Environmental distal renal tubular acidosis in Thailand: an enigma.

Distal renal tubular acidosis is a common health problem in northeastern Thailand, with the population background of the low potassium intake, low urine citrate, and decreased red blood cell Na-K adenosine triphosphatase (ATPase) activity and the environment of the high soil vanadium. The disease is usually seen in the people with low socioeconomic status in summer. The patients have decreased gastric acidity and low urine potassium. There are varying degrees of renal function from normal to impairment. Gastric hypoacidity is an important clue. Defects in H-K ATPase and anion exchange (AE2) mechanism are considered. The urine vanadium is higher in the patients than that of normal rural northeastern villagers. Inhibition of H-K ATPase by vanadium seems possible and requires more supporting evidence. AE1 gene mutation is noted in few patients. The cause of dRTA is not apparent. The AE2 gene and H-K ATPase gene remain to be studied. Both environmental and genetic factors could contribute to the pathogenesis of the disease.

Acidosis, Renal Tubular↗

The spectrum of renal tubular acidosis in paediatric Sjögren syndrome.

OBJECTIVES: Renal tubular acidosis (RTA) is a well-recognized extraglandular complication of adult Sjögren syndrome (SS) but has been reported only rarely in paediatric SS. We wished to describe the natural history of RTA in paediatric SS. METHODS: We performed a chart and literature review. Inclusion criteria were primary or secondary SS with onset before 18 yr of age, complicated by RTA before 18 yr of age. RESULTS: Twelve cases were identified: two from chart review and 10 from the literature. RTA was mostly associated with primary SS. RTA was detected at the onset of SS or up to 9 yr later. The clinical spectrum ranged from nearly silent to life-threatening, with plasma pH and serum potassium as low as 7.0 and 1.2 mEq/l, respectively. Hypokalaemia was present in 92%. Half the patients presented with profound weakness or paralysis, most likely from hypokalaemia. Proximal, distal and mixed RTA were detected, reflecting a diffuse 'tubulopathy' from interstitial nephritis, which was the predominant histopathological finding. Diabetes insipidus was the most frequent renal comorbidity. The RTA stabilized in 82% of the cases and resolved in one case. Only one patient had long-term unstable RTA. CONCLUSIONS: RTA is an under-recognized complication of paediatric SS. It can be life-threatening in the acute phase but generally has a good long-term renal outcome. SS should be considered in the older child with otherwise unexplained RTA. Likewise, RTA should be excluded in children and adolescents with SS who develop weakness, fatigue or growth failure. Early recognition would reduce long-term complications such as growth failure.

Acidosis, Renal Tubular↗

Recessive distal renal tubular acidosis in Sarawak caused by AE1 mutations.

Mutations of the AE1 (SLC4A1, Anion-Exchanger 1) gene that codes for band 3, the renal and red cell anion exchanger, are responsible for many cases of familial distal renal tubular acidosis (dRTA). In Southeast Asia this disease is usually recessive, caused either by homozygosity of a single AE1 mutation or by compound heterozygosity of two different AE1 mutations. We describe two unrelated boys in Sarawak with dRTA associated with compound heterozygosity of AE1 mutations. Both had Southeast Asian ovalocytosis (SAO), a morphological abnormality of red cells caused by a deletion of band 3 residues 400-408. In addition, one boy had a DNA sequence abnormality of band 3 residue (G701D), which has been reported from elsewhere in Southeast Asia. The other boy had the novel sequence abnormality of band 3 (Q759H) and profound hemolytic anemia.

Acidosis, Renal Tubular↗

Growth failure associated with medullary sponge kidney, due to incomplete renal tubular acidosis type 1.

A girl, 12 years of age, was referred for short stature. Clinical examination and laboratory investigations currently performed in a case of growth failure gave normal results. Renal echography revealed a hyper-echogenic renal medulla. An excretory urogram showed medullary sponge kidney with bilateral renal calculi. An ammonium chloride loading test revealed a defect in acid excretion and led to the diagnosis of incomplete renal tubular acidosis. Treatment with oral bicarbonate was associated with an increase in growth velocity.

Acidosis, Renal Tubular↗

Proximal renal tubular acidosis in pregnancy. A case report and literature review.

Renal tubular acidosis is usually associated with chronic renal conditions and is rarely encountered in pregnancy. It may be inherited causing osteomalacia and rickets in children or acquired following autoimmune diseases or following exposure to nephrotoxic agents. It is known to worsen during pregnancy and if left untreated may cause maternal and foetal morbidity or death. We report a 28-year-old woman, gravida 3 para 2, who presented at 30 weeks gestation with lethargy, weakness and generalized myalgia. Investigation revealed severe hypokalaemia and a systemic metabolic acidosis due to proximal renal tubular acidosis. Her previous pregnancies were both complicated by foetal losses at term. Following prompt correction of her electrolyte disturbance and metabolic acidosis, she went on to deliver a healthy female infant at term. Regular evaluation up to 1 year post-partum revealed mild persistence of her hypokalaemia. At 1 year, the infant showed no signs of the disorder and is growing normally.

Acidosis, Renal Tubular↗

Renal tubular acidosis associated with vitamin D-resistant rickets. Role of phosphate depletion.

3 children with vitamin D-resistant rickets (VDRR), and severe phosphate depletion had moderate metabolitic acidosis and evidence of impaired distal tubular acidifying mechanisms. Therapy with 1-alpha-OH-vitamin D3 and phosphate supplementation improved the clinical and radiological rachitic manifestations, and resulted in the normalization of systemic acid-base parameters as well as of tubular acidification. Profound phosphate depletion is another cause of acquired, reversible distal renal tubular acidosis (RTA).

Acidosis, Renal Tubular↗

Whole exome sequencing identifies three novel variants and establishes the molecular diagnosis of ATP6V0A4-related distal renal tubular acidosis in a lebanese infant.

BACKGROUND: Distal renal tubular acidosis (dRTA) is a rare inherited disorder characterized by impaired urinary acidification, leading to metabolic acidosis, hypokalemia, nephrocalcinosis, and growth impairment. Pathogenic variants in ATP6V0A4 are among the most common genetic causes of autosomal recessive dRTA. METHODS AND RESULTS: We report a Lebanese infant presenting with failure to thrive, recurrent vomiting, severe hyperchloremic metabolic acidosis, hypokalemia, and bilateral nephrocalcinosis, in whom whole-exome sequencing (WES) was performed to establish the molecular diagnosis and perform a comprehensive genomic evaluation. WES identified three novel variants, including a novel homozygous likely pathogenic ATP6V0A4 variant, consistent with the patient's phenotype. Two additional novel variants in TTN and CEP290 were also detected. Family segregation analysis confirmed the inheritance pattern of all three variants and refined the interpretation of the additional genomic findings. The patient showed sustained clinical and biochemical improvement to alkali therapy, with normalization of biochemical abnormalities and improvement in growth during follow-up. CONCLUSIONS: This report expands the molecular spectrum of ATP6V0A4-related dRTA and illustrates the clinical utility of comprehensive WES combined with segregation analysis for accurate molecular diagnosis, variant interpretation, genetic counseling, and the evaluation of additional genomic findings in rare inherited disorders.

Humans↗

An experimental renal acidification defect in patients with hereditary fructose intolerance. I. Its resemblance to renal tubular acidosis.

In three unrelated patients with hereditary fructose intolerance (HFI), but in none of five normal subjects, the experimental administration of fructose invariably induced a reversible dysfunction of the renal tubule with biochemical and physiological characteristics of renal tubular acidosis. During a state of ammonium chloride-induced acidosis, (a) urinary pH was greater than six and the rate of excretion of net acid (titratable acid plus ammonium minus bicarbonate) was inappropriately low, (b) the glomerular filtration rate remained unchanged or decreased modestly, and (c) urinary excretion of titratable acid increased briskly with diuresis of infused phosphate, although urinary pH changed little. The tubular dysfunction, which also includes impaired tubular reabsorption of alpha amino nitrogen and phosphate, persisted throughout administration of fructose and disappeared afterward. The tubular dysfunction was not causally dependent on hypoglucosemia, ammonium chloride-induced acidosis or osmotic diuresis. Rather, it appeared causally related to the fructose-induced metabolic abnormality of patients with HFI. The causal enzymatic defect, the virtual absence of fructose-1-phosphate aldolase, occurs in the kidney as well as in the liver of patients with HFI.

Acidosis↗

Effect of amphotercin B on urine acidification in rats: implications for the pathogenesis of distal renal tubular acidosis.

It has been proposed that distal renal tubular acidosis is a gradient-limited disorder an that the low urine Pco2 observed in this condition is caused by back diffusion of carbonic acid. This study was designed to examine this hypothesis using the amphotericin B model of gradient-limited distal renal tubular acidosis in rats. After induction of acute metabolic acidosis the minimum urine pH in 12 of 24 amphotericin B-treated rats exceeded 5.63 (mean 5.76 +/- 0.04), whereas it was 5.41 +/-0.04 in control rats. These animals with impaired urine acidification were presumed to have a gradient lesion and were studied in bicarbonate-loading experiments. The urine minus blood Pco2 gradient in these rats was 24.9 +/- 1.5 mm. Hg, a value similar to that of the control rats (26.7 +/- 2.1 mm. Hg). The presence of a normal urine minus blood Pco2 value in this experimentally induced gradient-limited type of acidification lesion indicates that a permeability defect for hydrogen ions was not associated with a similar defect for carbonic acid and that the urine minus blood Pco2 gradient is a valid index of distal nephron hydrogen ion secretion in amphotericin B-like gradient-type lesions.

Acidosis, Renal Tubular↗

Autosomal recessive distal renal tubular acidosis associated with Southeast Asian ovalocytosis.

BACKGROUND: A defect in the anion exchanger 1 (AE1) of the basolateral membrane of type A intercalated cells in the renal collecting duct may result in a failure to maintain a cell-to-lumen H+ gradient, leading to distal renal tubular acidosis (dRTA). Thus, dRTA may occur in Southeast Asian ovalocytosis (SAO), a common AE1 gene abnormality observed in Southeast Asia and Melanesia. Our study investigated whether or not this renal acidification defect exists in individuals with SAO. METHODS: Short and three-day NH4Cl loading tests were performed in 20 individuals with SAO and in two subjects, including their families, with both SAO and dRTA. Mutations of AE1 gene in individuals with SAO and members of the two families were also studied. RESULTS: Renal acidification in the 20 individuals with SAO and in the parents of the two families was normal. However, the two clinically affected individuals with SAO and dRTA had compound heterozygosity of 27 bp deletion in exon 11 and missense mutation G701D resulting from a CGG-->CAG substitution in exon 17 of the AE1 gene. Red cells of the two subjects with dRTA and SAO and the family members with SAO showed an approximate 40% reduction in sulfate influx with normal 4,4'-di-isothiocyanato-stilbene-2,2'-disulfonic acid sensitivity and pH dependence. CONCLUSION: These findings suggest that compound heterozygosity of abnormal AE1 genes causes autosomal recessive dRTA in SAO.

Acidosis, Renal Tubular↗

Type 4 renal tubular acidosis (sub-type 2) associated with idiopathic interstitial nephritis.

An 18-month-old girl presenting with anorexia and failure to thrive, was referred for adenoidectomy. Arterial hypertension was discovered on physical examination. Laboratory results revealed hyperkalaemic, hyperchloraemic, metabolic acidosis, with slight azotemia. Urinary aldosterone excretion and plasma renin were decreased. Renal biopsy showed idiopathic interstitial nephritis. The diagnosis of type 4 renal tubular acidosis, sub-type 2, i.e. primary hyporeninaemic secondary hypoaldosteronism was proposed. According to our knowledge, this disease has not previously been reported in young children, but is well known in azotaemic adults. We therefore propose the inclusion of this uncommon renal disease in the differential diagnosis of failure to thrive in childhood.

Acidosis, Renal Tubular↗

[Renal tubular acidosis with severe hypokalemic tetraparesis after ibuprofen intake].

HISTORY: A 72-year-old woman was admitted because of severe acute tetraparesis, more marked proximally. For six months she had been taking ibuprofen, up to 4800 mg daily, for a painful ulcer of the lower leg. INVESTIGATIONS: Biochemical tests revealed marked hypokalaemia (serum potassium 1.4 mmol/l) with a metabolic acidosis (pH 7.29). The ECG showed changes of hypokalaemia (ST-segment depression and U wave). TREATMENT AND COURSE: Within two days of administering potassium and bicarbonate the pareses completely regressed. Transitorily abnormal renal functions also rapidly normalized after ibuprofen had been discontinued. CONCLUSION: The biochemical findings suggest renal tubular acidosis, type 2, most likely caused by the excess intake of ibuprofen, a drug which can cause renal dysfunctions with life-threatening electrolyte abnormalities.

Acidosis, Renal Tubular↗

TTC19 and FMNL2 gene variants in a pediatric case of mitochondrial disorder with renal tubular acidosis.

Mitochondrial complex III deficiency caused by pathogenic variants in TTC19 is a heterogeneous disorder typically presenting with progressive neurological involvement in late childhood. Early-onset of disease with predominant renal manifestations are uncommon and may complicate diagnosis. We report a child presenting with developmental delay, failure to thrive, lactic acidosis, and distal renal tubular acidosis (dRTA), raising suspicion of an underlying mitochondrial disorder. Whole exome sequencing (WES) analysis identified a homozygous intron-exon boundary deletion of 31 bp (c.463-19_474del) in TTC19 predicted to disrupt splicing, with functional evidence demonstrating aberrant transcript formation, reduced gene expression, and mitochondrial dysfunction in patient-derived fibroblasts. Based on the biochemical findings, re-analysis of exome data revealed a novel homozygous canonical splice-site variant (c.783-1G>A) in FMNL2. The splicing assay showed the skipping of exon 9, and reduced expression in the fibroblasts. This case expands the clinical spectrum of TTC19-related mitochondrial complex III deficiency with early-onset renal tubular acidosis. While TTC19 is the most plausible primary disease-causing gene, the functional disruption of FMNL2 suggests a potential contributory role or association with the renal phenotype. Hence, these findings highlight the importance of genomic re-analysis along with functional studies in resolving complex multisystem disorders.

Female↗

[Distal renal tubular acidosis in primary biliary cirrhosis].

5 patients with primary biliary cirrhosis (PBC), 9 patients with compensated hepatic cirrhosis of different etiology and 12 control persons were tested for renal acidification after peroral CaCl2 administration and urine Na2SO4 and pCO2 infusion as well as the gradient between partial urine pressure and blood pressure after NaHCO3 application. Distal renal tubular acidosis (DRTA) was diagnosed in one patient with PBC, latent DRTA in other 2 patients with PBC. Not even one patient's acidification disorder was eliminated through an increased sodium application to the acidification site after Na2SO4 application. After NaHCO3 application, the gradient between the CO2 partial pressure in the urine and blood in both patients with PBC was, however, latent, DRTA normal. After pH gradient elimination in patients with PBC and DRTA, the hydrogen iont secretion is thus comparable with the control persons. Based on this study, the authors believe that the gradient type of DRTA is characteristic of primary biliary cirrhosis.

Acidosis, Renal Tubular↗

Hyperkalemic distal renal tubular acidosis associated with Rett syndrome.

Renal function was studied in a 7-year-old girl with Rett syndrome (RS) complicated by persistent hyperchloremic hyperkalemic metabolic acidosis. The acidosis was associated with a urine pH above 5.5, positive urinary anion gap and decreased potassium excretion. Plasma renin activity, aldosterone and cortisol levels were normal. Therapy with sodium bicarbonate failed to lower urine pH below 5.5 or increase potassium excretion. Hydrochlorothiazide administration resulted in a fall in urine pH below 5.5 and an increase in potassium excretion as a result of increased distal sodium delivery and increased sodium reabsorption in the distal nephron. We conclude that a voltage-dependent type of derangement in the distal nephron, rather than aldosterone deficiency, is responsible for the impairment in urinary acidification observed in this patient. Early detection of impaired renal acidification in RS may prevent or slow the progression of growth failure.

Acidosis, Renal Tubular↗