The Fanconi syndrome and mechanisms of tubular transport dysfunction

A review of renal tubular acidosis

OBJECTIVE

To review the current scientific literature on renal tubular acidosis (RTA) in people and small animals, focusing on diseases in veterinary medicine that result in secondary RTA.

DATA SOURCES

Scientific reviews and original research publications on people and small animals focusing on RTA.

SUMMARY

RTA is characterized by defective renal acid-base regulation that results in normal anion gap hyperchloremic metabolic acidosis. Renal acid-base regulation includes the reabsorption and regeneration of bicarbonate in the renal proximal tubule and collecting ducts and the process of ammoniagenesis. RTA occurs as a primary genetic disorder or secondary to disease conditions. Based on pathophysiology, RTA is classified as distal or type 1 RTA, proximal or type 2 RTA, type 3 RTA or carbonic anhydrase II mutation, and type 4 or hyperkalemic RTA. Fanconi syndrome comprises proximal RTA with additional defects in proximal tubular function. Extensive research elucidating the genetic basis of RTA in people exists. RTA is a genetic disorder in the Basenji breed of dogs, where the mutation is known. Secondary RTA in human and veterinary medicine is the sequela of diseases that include immune-mediated, toxic, and infectious causes. Diagnosis and characterization of RTA include the measurement of urine pH and the evaluation of renal handling of substances that should affect acid or bicarbonate excretion.

CONCLUSIONS

Commonality exists between human and veterinary medicine among the types of RTA. Many genetic defects causing primary RTA are identified in people, but those in companion animals other than in the Basenji are unknown. Critically ill veterinary patients are often admitted to the ICU for diseases associated with secondary RTA, or they may develop RTA while hospitalized. Recognition and treatment of RTA may reverse tubular dysfunction and promote recovery by correcting metabolic acidosis.

The impact of tubular dysfunction and its relationship with acute kidney injury in children

BACKGROUND

Tubular dysfunction can cause electrolyte disturbances with potentially serious consequences. We studied the epidemiology and outcomes of electrolyte disturbances and tubular dysfunction among critically ill children and evaluated their relationships with acute kidney injury (AKI).

METHODS

We conducted a prospective cohort study recruiting children aged 1 month to ≤ 18 years old admitted to the pediatric intensive care unit (PICU) from 6/2020 to 6/2021. The serum levels of sodium, potassium, calcium, phosphate, and magnesium were reviewed and simultaneous urinary investigations for tubular function were performed among children with electrolyte disturbances.

RESULTS

Altogether there were 253 episodes of admission. The median (interquartile) age was 4.9 (1.3-11.0) years and 58.1% were male. The median number of electrolyte disorders was 3 (2-4) types. Hypophosphatemia (74.2%), hypocalcemia (70.3%) and hypermagnesemia (52.9%) were the three commonest types of disturbances. Urinary electrolyte wasting was commonly observed among children with hypomagnesemia (70.6%), hypophosphatemia (67.4%) and hypokalemia (28.6%). Tubular dysfunction was detected in 82.6% of patients and urinary β2-microglobulin level significantly correlated with the severity of tubular dysfunction (p < 0.001). The development of tubular dysfunction was independent of AKI status. Tubular dysfunction was associated with mortality (p < 0.001) and was an independent predictor of PICU length of stay (LOS) (p < 0.001). The incorporation of the tubular dysfunction severity into the AKI staging system improved the prediction of PICU LOS.

CONCLUSIONS

Tubular dysfunction was associated with both morbidity and mortality in critically ill children and its assessment may help to capture a more comprehensive picture of acute kidney insult.

Fanconi Syndrome Associated with Long-term Treatment with Zoledronate

Intravenous bisphosphonate therapy is used to prevent fractures in the management of bone metastasis. However, it may induce renal damage. We herein report an 81-year-old woman with Fanconi syndrome and osteomalacia who had been diagnosed with metastatic breast cancer and received treatment with zolendronate for over 5 years. Her bone markers normalized after switching zolendronate to denosmab and starting vitamin D and mineral supplementation. This case shows that chronic renal damage induced by zolendronate can cause osteomalacia. In patients with intravenous zolendronate therapy, close monitoring of renal and bone markers is needed, even under long-term therapy.

Effect of gadopentetate dimeglumine on bone growth in zebrafish caudal fins

Compared with MR plain scanning, gadolinium (Gd)-enhanced MR scanning can provide more diagnostic information. Gadopentetate dimeglumine is generally used as an MR enhancement contrast agent in some countries. It is a member of linear Gd-based contrast agents (GBCAs) which are considered more likely to release free Gd ions (Gd³⁺) than macrocyclic GBCAs. Gd³⁺ is one of the most effective known calcium antagonists, and can compete with calcium ions (Ca²⁺) in Ca²⁺-related biological reactions. In this study, animal models of tissue regeneration were established by cutting the caudal fins of zebrafish, and the models were exposed with gadopentetate dimeglumine solution for different immersion times of 1, 3, and 5 min. Three GBCA exposures per week were performed in the first 3 weeks of the follow-up time. Morphological parameters such as regenerative area (RA), bone density, bone thickness and regenerative bone volume (RBV) were quantified using a camera and synchrotron radiation micro CT. RA decreased as total Gd intake increased in both the female group (ρ = -0.784, P < 0.0001) and the male group (ρ = -0.471, P = 0.011). The bone density of the regenerated bone increased after Gd exposure in the treated groups. The morphology of the regenerated bone from the treated groups became shorter and thicker. Our results showed that gadopentetate dimeglumine had osteogenic toxicity in zebrafish.

Disruption of mitochondrial functions involving mitochondrial permeability transition pore opening caused by maleic acid in rat kidney

Propionic acid (PA) predominantly accumulates in tissues and biological fluids of patients affected by propionic acidemia that may manifest chronic renal failure along development. High urinary excretion of maleic acid (MA) has also been described. Considering that the underlying mechanisms of renal dysfunction in this disorder are poorly known, the present work investigated the effects of PA and MA (1-5 mM) on mitochondrial functions and cellular viability in rat kidney and cultured human embryonic kidney (HEK-293) cells. Mitochondrial membrane potential (∆ψm), NAD(P)H content, swelling and ATP production were measured in rat kidney mitochondrial preparations supported by glutamate or glutamate plus malate, in the presence or absence of Ca²⁺. MTT reduction and propidium iodide (PI) incorporation were also determined in intact renal cells pre-incubated with MA or PA for 24 h. MA decreased Δψm and NAD(P)H content and induced swelling in Ca²⁺-loaded mitochondria either respiring with glutamate or glutamate plus malate. Noteworthy, these alterations were fully prevented by cyclosporin A plus ADP, suggesting the involvement of mitochondrial permeability transition (mPT). MA also markedly inhibited ATP synthesis in kidney mitochondria using the same substrates, implying a strong bioenergetics impairment. In contrast, PA only caused milder changes in these parameters. Finally, MA decreased MTT reduction and increased PI incorporation in intact HEK-293 cells, indicating a possible association between mitochondrial dysfunction and cell death in an intact cell system. It is therefore presumed that the MA-induced disruption of mitochondrial functions involving mPT pore opening may be involved in the chronic renal failure occurring in propionic acidemia.

Neuromuscular conditions and the impact of cystine-depleting therapy in infantile nephropathic cystinosis: A cross-sectional analysis of 55 patients

Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disease caused by biallelic mutations in the cystinosin gene, leading to cystine accumulation in various organs. The aim of this cross-sectional study was to investigate neuromuscular complications in a cohort of 55 patients (aged 2.8-41.3 years, median 18.5 years) with INC. Clinical examination, jumping mechanography, clinical neurophysiology, and muscle/nerve ultrasound were performed. Physical performance, measured by mechanography, was below average in all patients. However, this reduction in physical performance was not always detected by conventional muscle power assessment. Twenty-eight percent of patients had mostly mild axial weakness of the neck flexors and/or of the abdominal rectus muscles, the latter often presenting during childhood. One adult patient had generalized muscle weakness. Two patients had evidence of specific neuromuscular conditions, which may not have been directly related to cystinosis. 30% of patients presented with mild, 7% with moderate, and 5% with severe weakness of the intrinsic muscles of the hand. Muscle wasting was more pronounced in the older cystinosis patients with multiple organ complications. Sonographic increase in muscle echogenicity corresponded only with severe weakness. Electromyography of the intrinsic hand muscles, performed in selected patients, showed myopathic, neurogenic, or mixed myopathic-neurogenic abnormalities. A particularly important finding of this study is that the neuromuscular complications were largely independent from both the age of initiation of pharmacological cystine-depleting therapy and from adherence to treatment. Significant correlation was observed between better physical performance in jumping and cysteine levels in leukocytes.

Bioengineered Cystinotic Kidney Tubules Recapitulate a Nephropathic Phenotype

Nephropathic cystinosis is a rare and severe disease caused by disruptions in the CTNS gene. Cystinosis is characterized by lysosomal cystine accumulation, vesicle trafficking impairment, oxidative stress, and apoptosis. Additionally, cystinotic patients exhibit weakening and leakage of the proximal tubular segment of the nephrons, leading to renal Fanconi syndrome and kidney failure early in life. Current in vitro cystinotic models cannot recapitulate all clinical features of the disease which limits their translational value. Therefore, the development of novel, complex in vitro models that better mimic the disease and exhibit characteristics not compatible with 2-dimensional cell culture is of crucial importance for novel therapies development. In this study, we developed a 3-dimensional bioengineered model of nephropathic cystinosis by culturing conditionally immortalized proximal tubule epithelial cells (ciPTECs) on hollow fiber membranes (HFM). Cystinotic kidney tubules showed lysosomal cystine accumulation, increased autophagy and vesicle trafficking deterioration, the impairment of several metabolic pathways, and the disruption of the epithelial monolayer tightness as compared to control kidney tubules. In particular, the loss of monolayer organization and leakage could be mimicked with the use of the cystinotic kidney tubules, which has not been possible before, using the standard 2-dimensional cell culture. Overall, bioengineered cystinotic kidney tubules recapitulate better the nephropathic phenotype at a molecular, structural, and functional proximal tubule level compared to 2-dimensional cell cultures.

Hypophosphatemia in acute liver failure of a broad range of etiologies is associated with phosphaturia without kidney damage or phosphatonin elevation

Hypophosphatemia is a common and dangerous complication of acute liver failure (ALF) of various etiologies. While various mechanisms for ALF-associated hypophosphatemia have been proposed including high phosphate uptake into regenerating hepatocytes, acetaminophen (APAP)-associated hypophosphatemia was linked to renal phosphate wasting, and APAP-induced renal tubular injury was proposed as underlying mechanism. We studied 30 normophosphatemic and 46 hypophosphatemic (serum phosphate < 2.5 mg/dL) patients from the Acute Liver Failure Study Group registry with APAP- or non-APAP-induced ALF. Since kidney injury affects phosphate excretion, patients with elevated serum creatinine (>1.2 mg/dL) were excluded. Maximal amount of renal tubular phosphate reabsorption per filtered volume (TmP/GFR) was calculated from simultaneous serum and urine phosphate and creatinine levels to assess renal phosphate handling. Instead of enhanced renal phosphate reabsorption as would be expected during hypophosphatemia of non-renal causes, serum phosphate was positively correlated with TmP/GFR in both APAP- and non-APAP-induced ALF patients (R2 = 0.66 and 0.46, respectively; both P < 0.0001), indicating renal phosphate wasting. Surprisingly, there was no evidence of kidney damage based on urinary markers including neutrophil gelatinase-associated lipocalin and cystatin C even in the APAP group. Additionally, there was no evidence that the known serum phosphatonins parathyroid hormone, fibroblast growth factor 23, and α-Klotho contribute to the observed hypophosphatemia. We conclude that the observed hypophosphatemia with renal phosphate wasting in both APAP- and non-APAP-mediated ALF is likely the result of renal tubular phosphate leak from yet-to-be identified factor(s) with no evidence for proximal tubular damage or contribution of known phosphatonins.

[Acquired transient Fanconi syndrome after feeding jerky treats in dogs - A case series]

Between April 2018 and August 2019, 6 dogs with laboratory diagnostic evidence of Fanconi syndrome were presented to the Tierklinik Hofheim. The presumptive diagnosis was confirmed via urine amino acid analysis in all dogs. In 5 of the 6 dogs an alimentary origin was suspected, in 3 dogs the course of the disease could be followed. Supportive therapeutic measures and elimination of jerky treats from the dogs' diet improved the clinical symptoms in all dogs with known follow-up. This is the first case series of dogs with alimentary acquired Fanconi syndrome in Germany. The frequency of occurrence of the disease in that short period of time in only one small animal clinic suggests a significantly higher incidence than currently assumed.

MRI demonstration of gadolinium deposition in bone after monthly triple-dose gadopentetate dimeglumine and correlation with frequency of hypophosphatemia

OBJECTIVES

We retrospectively analyzed data of the BECOME trial to investigate whether serial administration of triple-dose (3-dose) gadopentetate dimeglumine would result in the development of T1 signal-to-noise (S/N) changes in the cranial diploic space and whether S/N changes correlated with on-study hypophosphatemia.

METHODS

Signal intensity analysis was performed on the first year's data of the BECOME trial using 3-dose Gd (14 months, maximum number of doses, 39, mean: 36). Routine blood and urine tests were obtained each month for safety monitoring. Linear mixed regression modeling with random intercept was used to analyze monthly signal-to-noise ratio (S/N = Bone/Air) using an ROI of the diploic space created from T2W images and overlaid on T1FS (T1 fat-saturated) images. Incidence of phosphate abnormalities was analyzed using the general estimation equation; correlation of phosphate and S/N change was achieved with type 3 test of fixed effects.

RESULTS

Cranial diploic space T1FS S/N increased over 14 months: S/N = 0.039 mean monthly increase (S.E. 0.008; p < 0.0001). Subjects with consistently normal phosphate levels (n = 32) experienced more of a S/N increase than patients with at least one episode of hypophosphatemia (n = 35) (0.057 vs. 0.023, respectively, p = 0.037). Those with moderate hypophosphatemia demonstrated no significant S/N increase.

CONCLUSION

Monthly administration of 3-dose gadopentetate dimeglumine is associated with development of increased S/N on T1FS imaging in the cranial diploic space, suggesting Gd retention in bone. Our data suggests MRI could be used as a noninvasive method of tracking Gd retention in bone, which was more pronounced in patients with normal phosphate levels.

A Complicated Pregnancy in an Adult with HNF4A p.R63W-Associated Fanconi Syndrome

Renal Fanconi syndrome (RFS) is characterised by generalised dysfunction of the proximal renal tubules, resulting in excessive urinary loss of solutes, most notably bicarbonate, and type II (proximal) renal tubular acidosis. It is a rare condition, and literature around its management through pregnancy is limited. We present the management of a 37-year-old woman with RFS secondary to the HNF4A p.R63W mutation, through her third pregnancy. She presented at 28 + 5 weeks with dehydration, low serum bicarbonate, and profound metabolic acidosis. Daily infusions of sodium bicarbonate were necessary, and the requirements increased throughout the pregnancy. She also demonstrated both fasting hypoglycaemia and episodes of postprandial hyperglycaemia which required complex management. Due to concerns around fetal health, an elective caesarean section was performed at 34 weeks, delivering a healthy baby girl. This case highlights the potential complexity of pregnancy in patients with RFS and the need for a multidisciplinary approach to its management.

Refeeding Syndrome

Refeeding syndrome describes the metabolic disturbances and clinical sequelae that occur in response to nutritional rehabilitation of patients who are moderate to severely malnourished. When risk factors are not identified and nutrition therapy is not managed appropriately, devastating consequences such as electrolyte depletion and imbalances, fluid overload, arrhythmia, seizure, encephalopathy, and death may occur. As this entity is often unrecognized, especially in pediatrics, becoming familiar with the pathophysiology, clinical manifestations, and management strategies will help clinicians caring for children avoid unnecessary morbidity and mortality. [Pediatr Ann. 2019;48(11):e448-e454.].

Proteomics analysis of blood plasma in HIV-infected patients with chronic kidney disease

BACKGROUND

Patients treated for human immunodeficiency virus (HIV) infection are prone to developing chronic kidney disease (CKD). Current methods used in assessing kidney function suffer inaccuracy in HIV-infected patients. This study aims to identify biomarkers that could complement existing methods of kidney assessment among HIV-infected subjects.

METHODS

Plasma protein profiling was performed for HIV patients with CKD presented with negative/trace proteinuria (non-proteinuric) (n = 8) and their matched non-CKD controls, using two-dimensional gel electrophoresis (2DE); selected protein candidates were identified using mass spectrometry. Subsequently, altered plasma abundance of protein candidates were verified using Western blotting in HIV-infected subjects with non-proteinuric CKD (n = 8), proteinuric CKD (n = 5), and their matched non-CKD controls, as well as in HIV-uninfected subjects with impaired kidney function (n = 3) and their matched controls.

RESULTS

Analysis of 2DE found significantly altered abundance of five protein candidates between HIV-infected patients with non-proteinuric CKD and without CKD: alpha-1-microglobulin (A1M), serum albumin (ALB), zinc-alpha-2-glycoprotein (AZGP1), haptoglobin (HP), and retinol binding protein (RBP4). Western blotting showed an increased abundance of A1M and HP in HIV-infected patients with non-proteinuric CKD compared to their non-CKD controls, whereas A1M, AZGP1, and RBP4 were significantly increased in HIV-infected patients with proteinuric CKD compared to their non-CKD controls. Such pattern was not found in HIV-uninfected subjects with impaired kidney function.

CONCLUSION

The data suggests four proteins that may be used as biomarkers of CKD in HIV-infected patients. Further validation in a larger cohort of HIV-infected patients is necessary for assessing the clinical use of these proposed biomarkers for CKD.

Sjögren's Syndrome Associated with Fanconi's Syndrome and Osteomalacia

BACKGROUND Sjögren's syndrome is a chronic inflammatory autoimmune disease, which is also known as sicca syndrome, due to the symptoms of dry eyes and dry mouth, and is associated with other connective tissue diseases and autoimmune diseases. Sjögren's syndrome can also be associated with renal involvement. Fanconi's syndrome is associated with impaired reabsorption in the proximal renal tubule associated with tubulointerstitial nephritis and is associated with renal tubular acidosis and hypophosphatemia. Osteomalacia is a rare association with Sjögren's syndrome, which may result from renal disease. CASE REPORT We report the case of a 34-year-old woman who presented with xerostomia, xerophthalmia, bone fractures, and osteomuscular pain. A Schirmer test showed reduced tear production, and a biopsy of a minor salivary gland of the lip, with high titers of antinuclear antibodies (ANA), and positive anti-SSA/Ro and anti-SSB/La antibodies confirmed the diagnosis of Sjögren's syndrome. Serum and urinary laboratories tests and clinical manifestations confirmed Fanconi's syndrome associated with osteomalacia. The patient was treated with potassium supplements, 25-hydroxyvitamin D (25(OH)D), hydroxychloroquine, mycophenolate mofetil, and prednisone, with a favorable response. CONCLUSIONS This case is of a rare association between Sjögren's syndrome, Fanconi's syndrome, and osteomalacia. Even though these are rare clinical associations, early detection can improve the quality of life and prevent further complications.

Ectopic germinal center and megalin defect in primary Sjogren syndrome with renal Fanconi syndrome

Background

This study reports the clinical and pathological features of 12 cases of primary Sjogren syndrome (pSS) with renal involvement presenting with proximal tubular dysfunction in a single center, and investigates the possible correlation of ectopic germinal center formation and megalin/cubilin down-expression.

Method

Clinical and pathological records were reviewed. Immunohistochemistry was carried out to detect megalin, cubilin, CD21 and IL-17 expression.

Results

Patients presented with different degrees of proximal renal tubule lesion and decreased estimated glomerular filtration rate (eGFR). Renal biopsy revealed tubulointerstitial nephritis, with tubular epithelial cell degeneration, tubular atrophy, interstitial inflammation and focal fibrosis. Immunohistochemistry revealed decreased expression of megalin and cubilin, two important multiligand protein receptors on the brush border of proximal tubular epithelial cells. IL-17 secreted by Th17 subtype effector T cells was diffusely detected in the renal proximal tubule, with a negative correlation of IL-17 and megalin expression. In addition, ectopic germinal centers characterized by CD21⁺ follicular dendritic cells were present in the renal interstitium. In patients with a decreased eGFR, treatment with 4 weeks of glucocorticoid therapy resulted in an improved eGFR in 75% of patients.

Conclusion

We report 12 cases of pSS characterized by Fanconi syndrome. The decreased megalin and cubilin expression may contribute to the proximal tubular reabsorption defect, possibly secondary to Th17 infiltration and formation of ectopic germinal centers.

Aminoaciduria Caused by Fanconi Syndrome in a Heifer

A case study of renal tubular dysfunction consistent with idiopathic Fanconi syndrome is reported in an 18-month-old Holstein heifer. The clinical, biochemical, and histopathological features are described. The heifer had clinical signs of growth retardation, wasting, and persistent diarrhea. Biochemical blood analysis identified hypokalemia, hyponatremia, and hypochloremia. Urinalysis identified glycosuria, proteinuria, and acidic pH. Histological examination of the kidney disclosed mild tubular necrosis with proteinaceous casts in the lumina of renal tubules. We performed LC-HRMS on urine to confirm Fanconi syndrome. Using this technique, we identified severe generalized aminoaciduria suggestive of idiopathic renal Fanconi syndrome in this heifer.

Cystinosis: a review

Cystinosis is the most common hereditary cause of renal Fanconi syndrome in children. It is an autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene encoding for the carrier protein cystinosin, transporting cystine out of the lysosomal compartment. Defective cystinosin function leads to intra-lysosomal cystine accumulation in all body cells and organs. The kidneys are initially affected during the first year of life through proximal tubular damage followed by progressive glomerular damage and end stage renal failure during mid-childhood if not treated. Other affected organs include eyes, thyroid, pancreas, gonads, muscles and CNS. Leucocyte cystine assay is the cornerstone for both diagnosis and therapeutic monitoring of the disease. Several lines of treatment are available for cystinosis including the cystine depleting agent cysteamine, renal replacement therapy, hormonal therapy and others; however, no curative treatment is yet available. In the current review we will discuss the most important clinical features of the disease, advantages and disadvantages of the current diagnostic and therapeutic options and the main topics of future research in cystinosis.

Mendelian disorders of PI metabolizing enzymes

More than twenty different genetic diseases have been described that are caused by mutations in phosphoinositide metabolizing enzymes, mostly in phosphoinositide phosphatases. Although generally ubiquitously expressed, mutations in these enzymes, which are mainly loss-of-function, result in tissue-restricted clinical manifestations through mechanisms that are not completely understood. Here we analyze selected disorders of phosphoinositide metabolism grouped according to the principle tissue affected: the nervous system, muscle, kidney, the osteoskeletal system, the eye, and the immune system. We will highlight what has been learnt so far from the study of these disorders about not only the cellular and molecular pathways that are involved or are governed by phosphoinositides, but also the many gaps that remain to be filled to gain a full understanding of the pathophysiological mechanisms underlying the clinical manifestations of this steadily growing class of diseases, most of which still remain orphan in terms of treatment. This article is part of a Special Issue entitled Phosphoinositides.

A case of Fanconi syndrome accompanied by crystal depositions in tubular cells in a patient with multiple myeloma

Fanconi syndrome (FS) is a rare condition that is characterized by defects in the proximal tubular function. A 48-year-old woman was admitted for evaluation of proteinuria. The patient showed normal anion gap acidosis, normoglycemic glycosuria, hypophosphatemia, and hypouricemia. Thus, her condition was compatible with FS. The M peak was found behind the beta globulin region in urine protein electrophoresis. Upon bone marrow examination, we found that 24% of cells were CD138+ plasma cells with kappa restriction. From a kidney biopsy, we found crystalline inclusions within proximal tubular epithelial cells. Thereafter, she was diagnosed with FS accompanied by multiple myeloma. The patient received chemotherapy and autologous stem cell transplantation, and obtained very good partial hematologic response. However, proximal tubular dysfunction was persistent until 1 year after autologous stem cell transplantation. In short, we report a case of FS accompanied by multiple myeloma, demonstrating crystalline inclusion in proximal tubular cells on kidney biopsy.

Proximal renal tubular acidosis: a not so rare disorder of multiple etiologies

Proximal renal tubular acidosis (RTA) (Type II RTA) is characterized by a defect in the ability to reabsorb HCO₃ in the proximal tubule. This is usually manifested as bicarbonate wastage in the urine reflecting that the defect in proximal tubular transport is severe enough that the capacity for bicarbonate reabsorption in the thick ascending limb of Henle's loop and more distal nephron segments is overwhelmed. More subtle defects in proximal bicarbonate transport likely go clinically unrecognized owing to compensatory reabsorption of bicarbonate distally. Inherited proximal RTA is more commonly autosomal recessive and has been associated with mutations in the basolateral sodium-bicarbonate cotransporter (NBCe1). Mutations in this transporter lead to reduced activity and/or trafficking, thus disrupting the normal bicarbonate reabsorption process of the proximal tubules. As an isolated defect for bicarbonate transport, proximal RTA is rare and is more often associated with the Fanconi syndrome characterized by urinary wastage of solutes like phosphate, uric acid, glucose, amino acids, low-molecular-weight proteins as well as bicarbonate. A vast array of rare tubular disorders may cause proximal RTA but most commonly it is induced by drugs. With the exception of carbonic anhydrase inhibitors which cause isolated proximal RTA, drug-induced proximal RTA is associated with Fanconi syndrome. Drugs that have been recently recognized to cause severe proximal RTA with Fanconi syndrome include ifosfamide, valproic acid and various antiretrovirals such as Tenofovir particularly when given to human immunodeficiency virus patients receiving concomitantly protease inhibitors such as ritonavir or reverse transcriptase inhibitors such as didanosine.

Cystinosis: the evolution of a treatable disease

Cystinosis is a rare autosomal recessive disorder involving lysosomal storage of the amino acid cystine due to a defect in the membrane transport protein, cystinosin. Since the introduction of kidney transplants and the availability of cystine-depleting medical therapy, this previously fatal disease was transformed into a treatable disorder. Renal allografts and medical therapy targeting the basic metabolic defect have altered the natural hisotry of cystinosis so drastically that patients have a life expectancy extending past 50 years. Consequently, early diagnosis and appropriate therapy are critically important. In this article, we offer a review of the manifestations of cystinosis, including the proximal tubular dysfunction of renal Fanconi syndrome, and discuss the prevention and treatment of the disorder's systemic complications. We focus on the nephropathic forms of cystinosis, aiming to assist nephrologists and other physicians to develop early recognition and appropriate management of cystinosis patients.

Fanconi syndrome in four non-basenji dogs exposed to chicken jerky treats

Four small-breed dogs were diagnosed with acquired Fanconi syndrome. All dogs ate varying amounts of chicken jerky treats. All dogs were examined for similar clinical signs that included, but were not limited to, lethargy, vomiting, anorexia, diarrhea, and altered thirst and urination. The quantity of chicken jerky consumed could not be determined; however, based on the histories obtained, the chicken jerky treats were a significant part of the diet and were consumed daily by all dogs. Extensive diagnostic testing eliminated other causes of the observed clinical signs, such as urinary tract infection and rickettsial disease. Glucosuria in the face of euglycemia or hypoglycemia, aminoaciduria, and metabolic acidosis confirmed the diagnosis of Fanconi syndrome. All dogs received supportive care, including IV fluids, antibiotics, gastroprotectants, and oral nutritional supplements. Three dogs exhibited complete resolution of glucosuria, proteinuria, and the associated azotemia; however, one dog remained azotemic, resulting in a diagnosis of chronic kidney disease.

Cadmium and cisplatin damage erythropoietin-producing proximal renal tubular cells

The concomitant manifestations of proximal renal tubular dysfunction and anemia with erythropoietin (Epo) deficiency observed in chronic cadmium (Cd) intoxication, such as Itai-itai disease, suggest a close local correlation between the Cd-targeted tubular cells and Epo-producing cells in the kidney. Therefore, we investigated the local relationship between hypoxia-induced Epo production and renal tubular injury in rats injected with Cd at 2 mg/kg twice a week for 8 months. Anemia due to insufficient production of Epo was observed in Cd-intoxicated rats. In situ hybridization detected Epo mRNA expression in the proximal renal tubular cells of hypoxic rats without Cd intoxication, and the Cd-intoxicated rats showed atrophy of Epo-expressing renal tubules and replacement of them with fibrotic tissue. A single dose of cisplatin at 8 mg/kg, which can induce clinical manifestations similar to those of Cd including renal tubular damage along with Epo-deficient anemia, resulted in Epo-expressing renal tubule destruction on day 4. These data indicate that Cd and cisplatin would induce anemia through the direct injury of the proximal renal tubular cells that are responsible for Epo production.

Paraquat-induced Fanconi syndrome

The ingestion of paraquat, a non-selective herbicide, can be fatal in humans. Paraquat is toxic to multiple organs, including the kidney, heart, gastrointestinal tract and central nervous system. Although paraquat has been established as one cause of acute tubular necrosis, Fanconi syndrome presenting as severe hypophosphataemia after paraquat intoxication has not been reported. Here, we report the case of a 44-year-old Korean woman who presented with generalized proximal tubular dysfunction including aminoaciduria, phosphaturia and glycosuria after paraquat intoxication. We found that severe hypophosphataemia induces deep drowsiness. Renal biopsy findings indicated the presence of acute tubular necrosis that may be reversible.

Environmental exposure to cadmium at a level insufficient to induce renal tubular dysfunction does not affect bone density among female Japanese farmers

Some recent research suggests that environmental exposure to cadmium, even at low levels, may increase the risk of osteoporosis, and that the bone demineralization is not just a secondary effect of renal dysfunction induced by high doses of cadmium as previously reported. To investigate the effect of exposure to cadmium at a level insufficient to induce kidney damage on bone mineral density (BMD) and bone metabolism, we conducted health examinations on 1380 female farmers from five districts in Japan who consumed rice contaminated by low-to-moderate levels of cadmium. We collected peripheral blood and urine samples and medical and nutritional information, and measured forearm BMD. Analysis of the data for subjects grouped by urinary cadmium level and age-related menstrual status suggested that cadmium accelerates both the increase of urinary calcium excretion around the time of menopause and the subsequent decrease in bone density after menopause. However, multivariate analyses showed no significant contribution of cadmium to bone density or urinary calcium excretion, indicating that the results mentioned above were confounded by other factors. These results indicate that environmental exposure to cadmium at levels insufficient to induce renal dysfunction does not increase the risk of osteoporosis, strongly supporting the established explanation for bone injury induced by cadmium as a secondary effect.

Urinary L-lactate excretion is increased in renal Fanconi syndrome

BACKGROUND

Measurement of l-lactate in body fluids is an established clinical tool to identify disorders of cellular respiration. However, there is very little known about the clinical value of urinary lactate measurements. We investigated urinary lactate excretion in children with renal Fanconi syndrome.

METHODS

Freshly voided urine samples were obtained from children with Fanconi syndrome and controls both with and without renal disease. Urine lactate was estimated by conversion to pyruvate in the presence of lactate dehydrogenase and NAD. The NADH produced was measured photometrically. Urine lactate was factored for urine creatinine.

RESULTS

Children with Fanconi syndrome had a significantly higher urine lactate/creatinine ratio [mean: 84 x 10(-2) mmol/mmol; 95% confidence interval (CI): 40.8-127.1 x 10(-2) mmol/mmol] than healthy controls (mean: 1.3 x 10(-2) mmol/mmol; CI: 1.1-1.5 x 10(-2) mmol/ mmol) and those with a variety of renal diseases (mean: 3.1 x 10(-2) mmol/mmol; CI: 1.8-4.5 x 10(-2) mmol/mmol).

CONCLUSIONS

Urinary lactate is increased in Fanconi syndrome. The increase is likely to be due to reduced lactate co-transport in the proximal tubule. Urinary lactate/creatinine has clinical utility as a sensitive test of disordered proximal renal tubular function.

Aristolochic acid-induced Fanconi's syndrome and nephropathy presenting as hypokalemic paralysis

Hypokalemic paralysis rarely is seen as the presenting feature in patients with Fanconi's syndrome. We describe a 60-year-old man who presented with the inability to ambulate on awakening in the morning. The pertinent history revealed he had consumed Chinese herbs for leg edema for 5 months. Physical examination was unremarkable except for extracellular fluid volume depletion and total paralysis of both lower extremities. Laboratory investigation showed hypokalemia (1.8 mEq/L), hyperchloremic metabolic acidosis (Cl-, 111 mEq/L, and HCO3-, 14.0 mEq/L), hypophosphatemia (0.9 mg/dL) with hyperphosphaturia, hypouricemia (1.3 mg/dL) with hyperuricosuria, and glycosuria, consistent with Fanconi's syndrome. Mild renal insufficiency (serum creatinine, 1.7 mg/dL) also was noticed. Blood and urine screens for heavy metals, autoantibodies, and monoclonal gammopathy were negative. A renal biopsy specimen revealed typical findings of aristolochic acid-associated nephropathy. Aristolochic acids were detected in the consumed Chinese herbs. This case highlights that consumption of Chinese herbs containing aristolochic acids may cause Fanconi's syndrome and should be considered as a cause of hypokalemic paralysis.

Role of megalin in renal handling of aminoglycosides

The role of megalin in tissue distribution of aminoglycosides was examined in normal rats and maleate-treated rats that shed megalin from the renal brush-border membrane. In normal rats, amikacin administered intravenously accumulated most abundantly in the renal cortex, followed by the renal medulla. No amikacin was detected in other tissues. Tissue distributions of amikacin were well correlated with megalin levels in each tissue. Bolus administration of gentamicin increased urinary excretion of megalin ligands (vitamin D binding protein and calcium), suggesting the competition between gentamicin and these megalin ligands in renal tubules. Ligand blotting showed that binding of (45)Ca(2+) to megalin was inhibited by aminoglycosides. Both megalin levels and amikacin accumulation in renal cortex were decreased by maleate injection. Then, amikacin accumulation recovered proportionate to megalin levels. These findings suggest that megalin is involved in the renal cortical accumulation of aminoglycosides in vivo. In addition, the interaction between aminoglycosides and calcium in the kidney may be due to the competition among these compounds to bind to megalin.

Hypophosphatemic rickets presenting as recurring pedal stress fractures in a middle-aged woman

Stress fractures frequently occur from overtraining. When stress fractures recur, underlying metabolic abnormalities should be ruled out. We report a middle-aged woman in whom such an evaluation demonstrated previously undiagnosed hypophosphatemic rickets after she presented with recurring stress fractures in her feet. Treatment with phosphate and calcitriol was associated with clinical improvement that would likely not have occurred without this intervention. Any patient with recurring stress fractures should be evaluated with several screening laboratory tests, metabolic bone x-rays, and a measurement of bone mineral density.

Abnormal serum uric acid levels in children

Measurement of the serum uric acid level, most commonly considered in adult patients, is frequently obtained inadvertently for pediatric patients because it is a standard component of many multichannel chemistry profiles offered by clinical laboratories. Most standard references for normal uric acid values do not take into account the impact of the metabolic changes in children at different ages on the uric acid level. A substantial number of childhood conditions may produce perturbations in the serum uric acid level. Knowledge of normal serum uric acid levels and of the conditions affecting those levels in children enables a more focused pursuit of underlying abnormalities.

Glycine attenuates Fanconi syndrome induced by maleate or ifosfamide in rats

It has become widely recognized that glycine (Gly) depletion predisposes isolated proximal tubules (PT) to necrotic cell damage induced by diverse insults and that Gly replacement in vitro is highly cytoprotective. However, the effectiveness of supplementation with Gly in vivo, where blood and tissue Gly normally are maintained at high levels, is incompletely defined. Our aim was to assess whether: (a) supplementation of Gly in drinking water of rats would attenuate the proximal tubule damage and the Fanconi syndrome (FS) induced by maleate (Mal), a classical proximal tubule toxin, or ifosfamide (IFO), an antineoplastic drug; and (b) to explore the mechanisms responsible for such effects, since Gly supplementation might be especially beneficial in treating the FS, where the kidney tends to waste amino acids. Rats received daily injection of Mal (2 mmol/kg) for two days without or with oral supplementation of 2% Gly. IFO, 50 mg/kg, was injected daily for five days without or with oral Gly. Control rats were injected with saline, without or with oral Gly. The results demonstrated that both Mal and IFO induced a FS characterized by wasting of amino and organic acids, glucose, and electrolytes, along with elevated plasma creatinine (Crn) and BUN, and decreased Crn clearance rate. Light microscopy revealed a necrotic lesion in the proximal tubules of the Mal group, but no necrosis after IFO. Gly strongly ameliorated the severity of renal necrosis and/or dysfunction induced by Mal or IFO, with significant decreases in total and fractional excretion of Na+, K+, PO4(3-) and glucose, decreased plasma BUN and Crn, and increased Crn clearance. Analysis of freeze-clamped cortical tissue showed substantial depletion of [Gly], [ATP] and [GSH] along with increased GSSG in Mal or IFO groups and correction of [Gly] and [ATP] with Gly supplementation, but no improvement with Gly of reduced gluthatione [GSH] or the ratio of reduced to oxidized gluthatione (GSH/GSSG). 31P-NMR analysis of the renal cortex indicated a decrease in Pi and various membrane phospholipids in Mal and IFO rats and prevention of this damage with Gly. These observations demonstrate that oral supplementation of Gly can provide protection against Mal or IFO-induced renal tubular cell dysfunction and structural damage. The lack of effect on glutathione oxidation and depletion suggests an action distal to toxin uptake and intracellular interactions, which is similar to the characteristics of Gly cytoprotection against diverse insults in vitro. The results also suggest modification by Gly of the primary toxicity of the agents and effects on phospholipid synthesis that could contribute to repair.

Modulation of sodium-coupled uptake and membrane fluidity by cisplatin in renal proximal tubular cells in primary culture and brush-border membrane vesicles

The proximal tubule appears to be the main target for the adverse effects of cis-diamminedichloroplatinum (II) (cDDP). We evaluated the early effects of cDDP at concentrations (3 to 67 microM) lower that those which alter cell viability, on three apical transport systems and on the physical state of the brush border membrane (BBM) in rabbit proximal tubule (RPT) cells in primary culture. The maximal effect, corresponding to a 30% decrease in Na(+)-coupled uptake of phosphate (Pi) and alpha-methylglucopyranoside (MGP) and a twofold increase in Na(+)-coupled alanine uptake, was obtained at 17 microM (5 micrograms/ml) cDDP and occurred through a modification of their affinity. At this concentration, cDDP increased BBM fluidity and decreased the BBM cholesterol content by 28%, without increasing the permeability of tight junctions. To clarify the role of cDDP-induced increase in BBM fluidity on alterations of Na(+)-coupled uptake, these parameters were also investigated in BBM vesicles isolated from rabbit renal cortex directly exposed to cDDP. cDDP induced a concentration-dependent inhibition of Na(+)-coupled uptake of MGP, Pi and alanine in BBM vesicles from the renal cortex, associated with a decrease in protein sulfhydryl content, without modifying BBM fluidity. Our findings strongly suggest that the cDDP-induced increase in BBM fluidity in RPT cells results from an indirect mechanism, possibly an alteration of cholesterol metabolism, and did not play a major role in the cDDP-induced inhibition of Na+/Pi and Na+/glucose cotransport systems that may be mainly mediated through a direct chemical interaction with essential sulfhydryl groups of the transporters.

Renal amino acid transport in adults with oxidative phosphorylation diseases

The clinical manifestations of mitochondrial DNA (mtDNA) mutations depend on a variety of factors including ratios of normal to abnormal mtDNA and tissue-specific differences in ATP production by oxidative phosphorylation (OXPHOS). In order to investigate the effects of OXPHOS defects on renal tubule function, we characterized sodium-coupled transport processes in six individuals with OXPHOS diseases. Pathogenic mtDNA mutations were identified in five of these individuals. Sodium coupled transport processes were evaluated by determining fractional excretions of amino acids, glucose, lactate, urate, and phosphate in patients and controls. Four of the six individuals had high fractional excretions of neutral amino acids, indicating abnormal renal tubule reabsorbtion of these amino acids. Abnormalities in fractional excretions of lactate, glucose, urate, and phosphate were less pronounced. These results demonstrate that sodium-coupled transport processes in the kidney are sensitive to OXPHOS impairment. When abnormalities in these processes are encountered, an OXPHOS disease should be included in the differential diagnosis.

Renal transplantation for infantile cystinosis: long-term follow-up

Renal transplantation for infantile cystinosis corrects renal failure and prolongs survival. However, after transplantation, the disease may develop in the allograft and continue to progress in nonrenal organs. We studied seven children (6 boys, 1 girl) with infantile cystinosis who received 11 renal transplants (3 cadaver, 8 living-related) between May 1969 and December 1986. The age at transplant ranged from 6 to 12 years (mean, 9.1 years). Four children received second renal transplants at a mean age of 17 years (range, 16 to 22 years). The mean period of follow-up was 138 +/- 47 months. Three children received cysteamine therapy prior to transplantation. Nonrenal complications of infantile cystinosis present before transplantation were photophobia (n = 3), corneal crystals (n = 5), hypothyroidism (n = 1), rickets (n = 6), and short stature (n = 7). Graft and patient survival did not differ from controls matched for the time of transplantation. Two patients died (1 pneumococcal sepsis, 1 respiratory failure due to pulmonary fibrosis) with functioning grafts 5 and 14 years posttransplant. Complications that developed posttransplant included photophobia (n = 1), corneal crystals (n = 2), hypothyroidism (n = 4), polyneuropathy (n = 1), pulmonary fibrosis (n = 1), abnormal electroencephalogram without clinical seizures (n = 1), bladder stones (n = 1), and diabetes mellitus (n = 2). One patient received a corneal transplant. All seven children failed to show improvement in growth following transplantation. Cystine crystals are present in graft-infiltrating cells, but do not seem to affect kidney allograft function.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic renal dysfunction in hemorrhagic fever with renal syndrome patients

During the last 9 years, 32 cases of hemorrhagic fever with renal syndrome (HFRS) have been diagnosed in our institution. Seven patients died. Twenty-three patients were discharged healthy while in another 2 some degree of renal dysfunction, which remained stable 12-15 months later, was evident. In 12 out of the 23 healthy individuals thorough examination of renal function was performed 1-5 years after their discharge. Three out of the 12 had renal tubular acidosis (RTA) type I (distal), complete or incomplete, and 2 (1 of whom also had incomplete RTA) had reduced urine concentrating ability. The development of chronic renal dysfunction was independent of the clinical severity of the acute illness.

Asymptomatic low molecular weight proteinuria in children

We reviewed the clinical features in 7 boys with asymptomatic low molecular weight proteinuria. The disease had first been reported by us in 1980. The distinctive features common to all patients were male dominance, asymptomatic proteinuria with a large amount of low molecular weight proteins, normal development and growth, normal renal function tests in childhood, and minimal histological changes in renal biopsy specimens. In 1990, 35 cases have been reported in Japan. Thus, asymptomatic low molecular weight proteinuria is not a rare disease and is one of the causes of isolated proteinuria. Furthermore, this condition is recognized as a new entity.

Fanconi syndrome, ichthyosis, dysmorphism, jaundice and diarrhoea--a new syndrome

We describe six infants, from consanguineous marriages, with a new syndrome comprising the Fanconi syndrome, ichthyosis, musculoskeletal abnormalities, jaundice and diarrhoea. In addition two of the infants were found to have abnormal platelet morphology--the grey platelet syndrome. No evidence of a recognised metabolic disorder was found in any of the six infants, nor did they appear to be typical of any previously described syndromes. Their progress was poor: they required high fluid and bicarbonate intakes and all died by the age of 6 months of dehydration, acidosis and sepsis.

Urine glyceraldehyde excretion is elevated in the renal Fanconi syndrome

We analyzed urinary constituents using GC/MS in 16 children with the renal Fanconi syndrome and 13 normal individuals. Urine glyceraldehyde levels were strikingly elevated in the renal Fanconi syndrome group (mean 5.1 +/- 4.8 mg/mg creatinine) compared to levels in the normal group (mean 0.04 +/- 0.04 mg/mg creatinine, P less than 0.001). Urine lactate levels were also elevated in the renal Fanconi syndrome group (mean 2.3 +/- 2.6 mg/mg creatinine) compared to normals (mean 0.01 +/- 0.01 mg/mg creatinine, P less than 0.003). Only small elevations of glyceraldehyde and lactate were found in urine from children with other renal disorders. Serum levels of glyceraldehyde and lactate were no greater in individuals with the Fanconi syndrome than in the normals. The fractional reabsorption of both glyceraldehyde and lactate was virtually complete in the normals, but was markedly impaired in the Fanconi syndrome patients where, in some cases, glyceraldehyde excretion greatly exceeded the excretion of creatinine. We conclude that marked glyceraldehyde excretion is a previously unrecognized feature of the renal Fanconi syndrome which may result from disordered proximal tubular glycolytic metabolism. Further studies will be required to determine the role of glyceraldehyde loss in the pathogenesis of this generalized disturbance of proximal tubular function.

Effects of succinylacetone on the uptake of sugars and amino acids by brush border vesicles

Infants with hereditary tyrosinemia excrete succinylacetone (SA) in their urine, and suffer from a reversible renal Fanconi syndrome with glycosuria and hyperaminoaciduria. Thus, we have examined the effects of 4 mM SA on rat renal brush border membrane vesicle uptake of sugars and amino acids. SA, unlike sodium maleate, significantly inhibits Na+-dependent vesicular sugar and amino acid uptake. 22Na-uptake, as well as membrane fluidity of the vesicles, are also affected by SA. Inhibition of glycine uptake by SA is reversible and competitive in nature, while alpha-CH3-D-glucoside uptake is non-competitively affected. We conclude, therefore, that SA has a more complex action on the rat renal tubule than sodium maleate, and is likely a much more physiologic model for study of the human renal Fanconi syndrome.

Life-threatening hyponatremia caused by vinblastine

Some days after the administration of a third bolus of ABVD (adriamycin, bleomycin, vinblastine, dacarbazine) a patient affected by immunoblastic lymphoma underwent a neurotoxic crisis. The episode lasted 1 week and was followed by a dramatic fall in plasma sodium (104 mEq I-1), associated with a proportionally lesser decrease in plasma chloride and phosphate. Despite the lowest plasma osmolality, detectable levels of circulating ADH were present. After 36 h the hyponatremic episode improved after the infusion of hypertonic sodium chloride. Nevertheless the patient lapsed into a hypotonic coma. The urinary concentrations of the main tubular enzymes (gamma-glutamyltranspeptidase, N-acetyl-glucosaminidase, alpha-glucosidase) proved very high and successively decreased slowly. The most likely cause of such hyponatremic episode is vinblastine. The drug acted through: (a) an already known inappropriate release of ADH, and (b) a hitherto unreported tubular lesion, which impaired the reabsorption of sodium and other coupled solutes.

Effects of succinylacetone on amino acid uptake in the rat kidney

Infants with hereditary tyrosinemia also have a renal Fanconi syndrome and excrete succinylacetone (SA). We have studied the effects of SA on rat renal tubular amino acid transport in vivo and in vitro using isolated renal tubules. Injection of SA produces increased clearance of several amino acids in the intact animal. In vitro SA causes a reversible inhibition of alpha-aminoisobutyric acid uptake, resulting from depressed low- and high-affinity transport systems. Addition of glutamate, succinate, or glucose, alone or in combination, did not restore transport. These observations suggest the usefulness of SA in the production of a physiologic animal model for the study of the human Fanconi syndrome.

Acute idiopathic tubulointerstitial nephritis: report of two cases and review of the literature

Two patients who presented with severe renal failure and evidence of generalized proximal tubular dysfunction were found to have severe diffuse acute tubulointerstitial nephritis on renal biopsy. No etiology could be found in either case. Both patients had dramatic improvement in renal function following steroid therapy. In the first reported case of its kind, one patient relapsed when steroids were withdrawn, but improved again with reinstitution of steroid therapy. These cases, as well as others in the literature, show that steroids are effective and may be necessary to improve renal function in some patients with acute idiopathic tubulointerstitial nephritis. Evidence of proximal tubular dysfunction is a clue to the presence of this disorder.

Glycogen accumulation in the pars recta of the proximal tubule in Fanconi syndrome

We reviewed the renal pathology in 10 cases of renal Fanconi syndrome. Five cases showed the Armanni-Ebstein lesion, i.e., clear glycogen-filled cells limited to the pars recta of the proximal tubules. The 5 cases included 2 siblings with a unique syndrome characterized by death in infancy, severe Fanconi syndrome, severe rickets, carnitine deficiency, and atrophy of the exocrine pancreas. Two other siblings had glycogen storage disease type XI. One of 4 cases of putative tyrosinemia had the lesion. The ultrastructure was studied in 2 cases. The Armanni-Ebstein lesion in these cases was morphologically indistinguishable from that seen in diabetic patients dying after prolonged hyperglycemia. Glycosuria is the only common factor in both diabetic hyperglycemia and the varied proximal tubular diseases studied. The mechanism of the glycogen accumulation in this short parts recta segment of the proximal renal tubule was further investigated by reviewing the renal histology in cases of glycogen storage disease types I, II, III, and VIII. None showed the Armanni-Ebstein lesion, but type I showed glycogen deposition throughout the proximal tubule. Thus, the Armanni-Ebstein lesion is not the result of an enzymatic deficiency for glycogen synthesis in the convoluted tubules.

Effects of succinylacetone on methyl alpha-D-glucoside uptake by the rat renal tubule

Succinylacetone, a catabolic end-product of tyrosine, is excreted in large quantities in urine from individuals with hereditary tyrosinemia and the Fanconi syndrome. Succinylacetone inhibits rat renal tubular concentrative uptake of the glucose transport analogue, methyl alpha-D-glucoside, in a noncompetitive and reversible fashion. This compound also depresses oxygen consumption by the rat renal tubule without fine structural damage to mitochondria. It is concluded that succinylacetone may be a useful probe in elucidation of the biochemical mechanism underlying the human Fanconi syndrome.

Cystinosis presenting with features suggesting Bartter syndrome. Case report and literature review

Features suggestive of Bartter syndrome (hypokalemia, hypochloremic metabolic alkalosis, and normal blood pressure despite hyperreninemia and hyperaldosteronism) were found in a 5-year-old black child with cystinosis and Fanconi syndrome. Review of his medical records revealed that these abnormalities had probably been present when he first became clinically ill at 2 years of age. Sodium and potassium chloride supplementation lead to improved growth and strength, partial correction of his electrolyte abnormalities, and a decrease in markedly elevated plasma renin activity. Literature review disclosed a similar presentation in four Caucasian children with cystinosis. Biochemical findings compatible with Bartter syndrome can occur together with evidence of generalized proximal renal tubular dysfunction (Fanconi syndrome) in nephropathic cystinosis.

Renal tubular acidosis

In the past decade major advances in our understanding of renal tubular hydrogen ion secretion and bicarbonate reabsorption have provided new insight into the pathophysiology of renal tubular acidosis. Thus "fragment to fragment clings" and the number of disorders categorized within the syndrome grows, until we have come to know and name four types, with many subtypes. We hope this new perspective provides a basis for the physician to recognize renal tubular acidosis in its several forms so that an informed decision may be arrived at in choosing the best therapy. The physician may also be prepared to reasonably project the prognosis for each patient. We also hope that our detailed examination of renal acidification will provide a reference for delineation of new clinical expressions of acid-base disorders and kidney malfunction certain to be described in the years ahead.