Autosomal dominant distal renal tubular acidosis in two pediatric patients with mutations in the SLC4A1 gene. Can the maximum urinary pCO2 test be normal?

Primary distal renal tubular acidosis (dRTA) is a rare tubulopathy characterised by the presence of hyperchloremic metabolic acidosis. It is caused by the existence of a defect in the function of the H+ -ATPase located on the luminal side of the α-intercalated cells or the Cl - HCO3- (AE1) anion exchanger located on the basolateral side. Patients do not acidify the urine after acid overload (NH4Cl) or after stimulating H+ secretion by obtaining a high intratubular concentration of an anion such as chlorine (pH is measured) or HCO3- (urinary pCO2 is measured). We present a family with autosomal dominant dRTA produced by a heterozygous mutation in the SLC4A1 gene in which the two paediatric members showed a test of normal maximum urinary pCO2. Our hypothesis is that since the H + -ATPase is intact, at least initially, the stimulation induced by intratubular electronegativity to secrete H + could be effective, which would allow the maximum urinary pCO2 to be paradoxically normal, which could explain the onset, moderate presentation of symptoms and late diagnosis in patients with this mutation. This is the first documented case of a dominant dRTA in Mexico.

Pattern of hereditary renal tubular disorders in Egyptian children.

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

An Infant Case of Transient Distal Renal Tubular Acidosis and Fanconi Syndrome Caused by Rotavirus Gastroenteritis.

We report an infant case of transient distal renal tubular acidosis and Fanconi syndrome caused by rotavirus gastroenteritis. A 10-month-old boy was admitted to the hospital because of frequent vomiting, lack of vitality, and dehydration. He was diagnosed with rotavirus gastroenteritis on account of his positive stool rotavirus antigen test. Although he presented with acidemia and severe mixed metabolic acidosis, he also had a urine pH of 6.0, indicating impaired urinary acidification. Therefore, he was diagnosed with distal renal tubular acidosis. On the third day of hospitalization, a relatively low %tubular reabsorption of phosphate level with hypophosphatemia, increased fractional excretion of uric acid with hypouricemia, and high urinary ß2-microglobulin levels were observed. Moreover, he was diagnosed with Fanconi syndrome on account of multiple proximal tubular dysfunctions. After remission of rotavirus gastroenteritis, the signs of renal tubular dysfunction improved. This was a case of rotavirus gastroenteritis-caused transient distal renal tubular acidosis and Fanconi syndrome. Severe metabolic acidosis resulted from anion-gap metabolic acidosis due to acute kidney injury by rotavirus gastroenteritis and normal anion-gap acidosis due to renal tubular acidosis. When renal tubular acidosis is associated with a disease that causes anion-gap metabolic acidosis, mixed metabolic acidosis occurs and becomes exacerbated. Furthermore, it is important to consider the complications of renal tubular acidosis in the case of severe metabolic acidosis.

Renal tubular acidosis without interstitial nephritis in Sjögren's syndrome: a case report and review of the literature.

BACKGROUND: Renal tubular acidosis is the principal clinical feature associated with tubulointerstitial nephritis in patients with primary Sjögren's syndrome. Renal tubular dysfunction due to interstitial nephritis has been considered the underlying pathophysiology connecting renal tubular acidosis and primary Sjögren's syndrome. However, the detailed mechanisms underlying the pathophysiology of renal tubular acidosis in primary Sjögren's syndrome is not fully understood. CASE PRESENTATION: A 30-year-old woman was admitted with complaints of weakness in the extremities. The patient was hospitalized thirteen years earlier for similar issues and was diagnosed with hypokalemic paralysis due to distal renal tubular acidosis with primary Sjögren's syndrome. This diagnosis was based on a positive Schirmer's test. Besides, anti-Sjögren's syndrome-related antigen A was also detected. Laboratory tests indicated distal RTA; however, a renal biopsy showed no obvious interstitial nephritis. Laboratory tests conducted during the second admission indicated distal renal tubular acidosis. Therefore, a renal biopsy was performed again, which revealed interstitial nephritis. Histological analysis of acid-base transporters revealed the absence of vacuolar type H+-ATPases in the collecting duct. The vacuolar type H+-ATPase was also absent in the past renal biopsy, suggesting that the alteration in acid-base transporters is independent of interstitial nephritis. CONCLUSIONS: This case study demonstrates that vacuolar-type H+-ATPases are associated with distal renal tubular acidosis, and distal renal tubular acidosis precedes interstitial nephritis in patients with primary Sjögren's syndrome.

Severe Hypokalemia Complicated by Acute Myopathy: Initial Manifestation of Primary Sjögren's Syndrome-Associated Renal Tubular Acidosis.

BACKGROUND Severe hypokalemia, which often causes life-threatening malignant arrhythmias, is usually first diagnosed in the Emergency Department (ED). It is important to note that hypokalemia is often closely and complexly related to renal tubular acidosis (RTA) associated with autoimmune diseases such as Sjögren's syndrome (SS), especially in females with acute myopathy or acute liver injury (ALI). Severe hypokalemia can directly cause muscle injury, which can lead to hyper-creatine kinaseemia (HCK) and ALI, while SS can also directly cause hypokalemia, HCK, and even ALI and renal tubular/interstitial injury. Therefore, by reporting a rare case of SS-associated RTA (SS-RTA), we systematically reviewed the relationship between SS-RTA and severe hypokalemia, which may be beneficial to increase attention on this topic. CASE REPORT A 35-year-old female patient who presented to the ED primarily for limb weakness symptoms was initially diagnosed with severe hypokalemia, acute myopathy, and ALI. She was eventually diagnosed with primary SS (pSS) and SS-RTA, although she did not present with the typical dry mouth, dry eyes, and other clinical manifestations of SS. CONCLUSIONS Severe hypokalemia is a serious life-threatening emergency, and although the differential diagnosis is very broad, we should be aware of RTA associated with autoimmune diseases such as SS in female patients, especially when combined with clinical manifestations such as acute myopathy and ALI that cannot be explained by other causes. Simultaneously, we hope to be able to guide emergency physicians encountering similar patients to complete the diagnostic and therapeutic process.

A report of three cases of patients with tubulointerstitial nephritis with IgM-positive plasma cells, treatment, and serum-IgM as a sensitive marker for relapse.

BACKGROUND: Tubulointerstitial nephritis with IgM-positive plasma cells (IgMPC-TIN) is a newer disease about which there are many unclear points. Glucocorticoid therapy is effective in many cases of IgMPC-TIN; however, relapse during glucocorticoid tapering has been reported. Relapse and its treatment are poorly defined. CASE PRESENTATION: Case 1 was a 61-year-old man with renal dysfunction and proteinuria. Tubulointerstitial nephritis and IgM-positive plasma cells were observed in a renal biopsy. He was diagnosed with IgMPC-TIN accompanied by Fanconi syndrome and distal renal tubular acidosis (d-RTA). Prednisolone (PSL; 30 mg daily, 0.45 mg/kg/day) treatment was highly effective, and PSL was gradually tapered and discontinued after 1 year. However, 1 month after PSL discontinuation, therapeutic markers were elevated. Therefore, PSL (10 mg daily, 0.15 mg/kg/day) was administered, and the markers indicated improvement. Case 2 was a 43-year-old woman referred for renal dysfunction and proteinuria. Laboratory data revealed that she had primary biliary cholangitis (PBC), d-RTA, and Fanconi syndrome. A renal biopsy showed accumulation of IgM-positive plasma cells in the tubulointerstitium without any glomerular changes. A diagnosis of IgMPC-TIN was made and the patient was started on PSL (35 mg daily, 0.6 mg/kg/day). Therapeutic markers decreased immediately and PSL was discontinued after 1 year. Three months later, the proteinuria and Fanconi syndrome worsened. PSL treatment was restarted (20 mg daily, 0.35 mg/kg/day) and markers indicated improvement. Case 3 was a 45-year-old woman with renal dysfunction and proteinuria. Tubulointerstitial nephritis and IgM-positive plasma cells were observed in a renal biopsy. The patient had PBC, Sjögren syndrome, d-RTA, and Fanconi syndrome, and the diagnosis of IgMPC-TIN was made. The patient was started on PSL (30 mg daily, 0.4 mg/kg/day) and disease markers decreased immediately. However, when PSL was tapered to 15 mg daily (0.2 mg/kg/day), the patient's serum IgM levels increased; therefore, we maintained the PSL at 15 mg daily (0.2 mg/kg/day). CONCLUSION: We report three cases of relapsed IgMPC-TIN associated with reduction or discontinuation of glucocorticoid therapy. In these cases, elevation of serum IgM preceded that of other markers such as urinary ß2-microglobulin, proteinuria, and glycosuria. We recommend monitoring serum IgM levels while tapering glucocorticoids; a maintenance dose of glucocorticoid should be considered if relapse is suspected or anticipated.

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.

[Type IVa2 urinary lithiasis and associated pathologies: About 3 cases]. / Lithiase urinaire de type IVa2 et pathologies associées : à propos de 3 cas.

INTRODUCTION: Urinary lithiasis is a very common condition. The morpho-constitutional analysis of urinary stones is important for etiological diagnosis. It guides the explorations and the specific management. Type IVa2 stones are rare, have particular morphology and correspond to very targeted pathologies. We propose to report our cases of patients diagnosed with type IVa2 urinary lithiasis. METHODS: Our retrospective work focused on three cases of patients with the morphological type of renal lithiasis IVa2, collected between 2008 and 2020 in the Medicine A Department of Charles Nicolle Hospital in Tunis. RESULTS: All three patients were female; average age 37.6 years. The clinical symptomatology was identical marked by renal colic with recurrent episodes. The presence of a type IVa2 stone, isolated or associated with other components, guided the etiological investigation to look for a secondary or primary cause of distal renal tubular acidosis. We retained the diagnosis of a primary hyperparathyroidism in one case and a primary Gougerot-Sjögren's syndrome in the second case, and probable in the last case. CONCLUSION: Determination of urolithiasis nature (morphological and chemical), although carried out late, was of major interest to us and allowed us to make the diagnosis of distal tubular acidosis.

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.

Distal renal tubular acidosis, autoimmune thyroiditis, enamel hypomaturation, and tooth agenesis caused by homozygosity of a novel double-nucleotide substitution in SLC4A4.

BACKGROUND: Mutations in SLC4A4 have been reported to be associated with proximal renal tubular acidosis (RTA), short stature, band keratopathy, cataract, glaucoma, and hypoplastic-type amelogenesis imperfecta. In this study, the authors describe the clinical manifestations, and investigate the molecular etiology, in a patient with RTA. CASE DESCRIPTION: The authors report on a girl with distal RTA who carried a novel homozygous base substitution of 2 consecutive base pair variants (NM_001098484.3:c.808-2A>C and NM_001098484.3:c.808-1G>C) in the SLC4A4 gene. The patient had clinical manifestations of autoimmune thyroiditis and distal RTA, including hypercalciuria, nephrocalcinosis, and nephrolithiasis. In addition to the presence of hypoplastic-type amelogenesis imperfecta, generalized enamel hypomaturation, a feature seen in mice lacking Slc4a4, was also observed in the patient. The basic defect in this patient appeared to be impaired hydrogen ion secretion, leading to an inability to acidify the urine, resulting in alkaline urine (despite a normal serum anion gap), hypokalemic, and hyperchloremic metabolic acidosis. The pulp stones found in the patient may likely be the consequences of a disrupted acid-base homeostatic environment that precipitated mineral deposits. Even with proper treatments for distal RTA, the patient has had frequent recurrences of band keratopathy, pupillary membrane, and cataract. PRACTICAL IMPLICATIONS: This is the first report of distal RTA, autoimmune thyroiditis, tooth agenesis, enamel hypomaturation, and pulp stones associated with an SLC4A4 mutation. It is important for dentists to be aware that amelogenesis imperfecta in patients may be a sign of systemic diseases including RTA, nephrocalcinosis, or nephrolithiasis.

Secondary distal renal tubular acidosis and sclerotic metabolic bone disease in seronegative spondyloarthropathy.

Adults with distal renal tubular acidosis (dRTA) commonly present with hypokalaemia (with/without paralysis), nephrolithiasis/nephrocalcinosis and vague musculoskeletal symptoms. All adults with dRTA should be thoroughly evaluated for systemic diseases, certain medications and toxins. The leading cause of acquired or secondary dRTA in adults is primary Sjögren syndrome (SS); however, other collagen vascular diseases (CVDs) including seronegative spondyloarthropathy (SSpA) may at times give rise to secondary dRTA. Metabolic bone disease is often encountered in adults with dRTA, and the list includes osteomalacia and secondary osteoporosis; sclerotic metabolic bone disease is an extremely rare manifestation of dRTA. Coexistence of dRTA and sclerotic bone disease is seen in primary dRTA due to mutation in CA2 gene and acquired dRTA secondary to systemic fluorosis. Primary SS and SSpA, rarely if ever, may also lead to both secondary dRTA and osteosclerosis. Circulating autoantibodies against carbonic anhydrase II and possibly calcium sensing receptor may explain both these features in patients with CVD.

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.

Acute Flaccid Quadriparesis Because of a Rare Systemic Cause.

Sjogren's syndrome is a chronic slowly progressive autoimmune disease characterized by lymphocytic infiltration of exocrine glands resulting in xerostomia and dry eyes. The syndrome has wide clinical spectrum from organ specific exocrionopathy to systemic manifestation. The disease can present alone or with other autoimmune diseases like RA, SLE, Scleroderma, autoimmune thyroid disease etc. Prevalence of primary Sjogren's is 0.5-1% and of secondary Sjogren's is 5-20%. Renal involvement is rare and can either be tubulointerstial or glomerular. Based on biopsy reports in the available literature, tubulointerstitial nephritis (TIN) is the most common histological abnormality, followed by glomerulonephritis as a distant second.1 Distal Renal tubular Acidosis is the most common manifestation of TIN. We report a case of a 35 year female with acute onset motor weakness (quadriparesis) with hypokalemia with NAGMA with distal RTA. Patient was diagnosed with Secondary Sjogren's and managed accordingly.

Primary Sjögren's syndrome manifesting as sclerotic metabolic bone disease.

Primary Sjögren's syndrome (pSS) is a chronic slowly progressive autoimmune disease characterised by lymphocytic infiltration of salivary and lacrimal glands with varying degree of systemic involvement. Renal involvement, a recognised extraglandular manifestation of pSS, is commonly related to tubular dysfunction and generally manifests as distal renal tubular acidosis (RTA), proximal RTA, tubular proteinuria and nephrogenic diabetes insipidus. Untreated long-standing RTA is known to cause metabolic bone disease. Here, we present the report of a patient with sclerotic metabolic bone disease related to pSS with combined distal and proximal RTA and negative workup for other causes of sclerotic bone disease. A significant clinical and biochemical improvement, including recovery of proximal tubular dysfunction, was noted with alkali therapy. This case suggests the need to consider pSS in the diagnostic algorithm of a patient presenting with sclerotic bone disease.

Premature onset of Sjögren's syndrome is prone to be complicated with renal tubular acidosis.

Sjögren's syndrome (SS) is a common systemic autoimmune disease. SS usually occurs among middle-aged women with a peak incidence age of approximately 50 years old. Kidney involvement is relatively uncommon in SS, which is mostly characterized as interstitial nephritis and may result in renal tubular acidosis (RTA). But premature onset of SS seems to be prone to RTA. Here we reported four cases of premature onset SS who developed into RTA at a relatively young age and three of whom suffered from severe osteomalacia. All of them shared a disease onset under age eighteen. Two of them presented hypokalemic periodic paralysis initially, one presented purpura and one endured xerophthalmia at first place. Three of them complicated with osteomalacia under age thirty. All the 4 cases didn't receive proper medical care in time due to a prolonged delay of diagnosis. We aim to raise the alarm over misdiagnosis/underdiagnosis of the disorder among young people.

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.