Tubular Diseases and Stones Seen From Pediatric and Adult Nephrology Perspectives

The tubular system of the kidneys is a complex series of morphologic and functional units orchestrating the content of tubular fluid as it flows along the nephron and collecting ducts. Renal tubules maintain body water, regulate electrolytes and acid-base balance, reabsorb precious organic solutes, and eliminate specific metabolites, toxins, and drugs. In addition, decisive mechanisms to adjust blood pressure are governed by the renal tubules. Genetic as well as acquired disorders of these tubular functions may cause serious diseases that manifest both in childhood and adulthood. This article addresses a selection of tubulopathies and the underlying pathomechanisms, while highlighting the important differences in pediatric and adult nephrology care. These range from rare monogenic conditions such as nephrogenic diabetes insipidus, cystinosis, and Bartter syndrome that present in childhood, to the genetic and acquired tubular pathologies causing hypertension or nephrolithiasis that are more prevalent in adults. Both pediatric and adult nephrologists must be aware of these conditions and the age-dependent manifestations that warrant close interaction between the two subspecialties.

A clinical approach to tubulopathies in children and young adults

Kidney tubules are responsible for the preservation of fluid, electrolyte and acid-base homeostasis via passive and active mechanisms. These physiological processes can be disrupted by inherited or acquired aetiologies. The net result is a tubulopathy. It is important to make a prompt and accurate diagnosis of tubulopathies in children and young adults. This allows timely and appropriate management, including disease-specific therapies, and avoids complications such as growth failure. Tubulopathies can present with a variety of non-specific clinical features which can be diagnostically challenging. In this review, we build from this common anatomical and physiological understanding to present a tangible appreciation of tubulopathies as they are likely to be clinically encountered among affected children and young adults.

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.

[Kidney injury in children and adolescents with leptospirosis in France]

INTRODUCTION

Leptospirosis is an anthropozoonosis with polymorphic clinical symptoms and a high variability of severity, ranging from flu-like syndrome to severe acute kidney injury. This disease is highly incident in tropical regions but there is a trend towards increasing incidence in metropolitan France and in Reunion Island. The objective of this study was to describe the epidemiological, clinical, laboratory and therapeutic characteristics of the pediatric leptospirosis in metropolitan France and in Reunion Island.

PATIENTS AND METHODS

We performed a retrospective analysis of leptospirosis cases hospitalized in University hospitals where members of the Paediatric Nephrology Society work in France between January 2008 and December 2020, 6 centers reported leptospirosis cases, one center had one patient in consultation but lack of available data and 10 centers did not find any case.

RESULTS

A total of 21 cases were reported (mean age 13.4±3.4years), mostly boys (ratio 6:1). Out of 21 patients, 95% had fever, 71% were presenting with myalgia, 81% with thrombocytopenia, and 76% with gastrointestinal symptoms. Regarding kidney impairment, 18 patients (86%) had acute kidney injury, including 4 (19%) with oligoanuria, but none of them required acute dialysis. About 30% of patients had biological signs of tubulopathy including hypophosphatemia, hypokalemia, or tubular proteinuria. No death due to the disease occurred. The therapeutic management followed the current guidelines with the use of antibiotic therapy by amoxicillin or 3rd generation cephalosporins with symptomatic treatment. When there was biological control after exit, creatinine decreased.

DISCUSSION

In this multicenter retrospective study, we report 21 children with leptospirosis with a significant proportion of acute kidney injury, the outcome was favorable. Children do not seem to be at high risk of chronic kidney disease progression but nephrology follow-up has not been systematically carried out. Compared to studies performed in adults, the prognosis was better and hepatic impairment was rare. Compared to other pediatric studies, conjunctivitis was not a common symptom but kidney injury and survival appeared to be similar. Children were presenting with anicteric renal presentation. The casebook wasn't exhaustive and didn't include the other overseas territories, which account for the highest proportion of leptospirosis infection.

CONCLUSION

Leptospirosis is an infection which may lead to multivisceral failure with kidney involvement conditioning the outcome. Despite a better prognosis in children, it remains important to quickly diagnose this infection in order to start appropriate antibiotic therapy and perform a kidney function monitoring.

Gitelman syndrome with normocalciuria - a case report

Background

Gitelman Syndrome (GS) is a hereditary tubulopathy associated with a biallelic inactivating mutations of the SLC12A3 gene encoding the thiazide-sensitive sodium-chloride cotransporter (NCCT). The typical clinical manifestation is a hypokalemic metabolic alkalosis with significant hypomagnesemia, and low urinary calcium excretion. Hypocalciuria is widely believed to be a hallmark of GS that distinguishes it from Barter’s syndrome, presenting as hypercalciuria. The pathomechanism of hypocalciuria in GS is not fully elucidated. Up to date, a clinical course of GS with normocalciuria has been reported only in men, while women have a milder course of the disease with typical hypocalciuria, which is believed as the result of sex hormone. Additionally, there is a growing evidence that calcium channels of the distal nephron could be regulated by a variety of hormones, including aldosterone (Aldo).

Case presentation

We present the case of a 28-year-old Caucasian woman with asymptomatic, chronic hypokalemia, hypomagnesemia, hypochloremic alkalosis and normal urinary calcium excretion. A high renin levels with normal concentration of Aldo in serum have also been found. The values of blood pressure were low. Based on genetic studies, two heterozygous mutations in the trans position were confirmed: c.2186G>T (p.Gly729Val) and c.1247G>C (p.Cys416Ser) in the SLC12A3 gene, which ultimately confirmed the diagnosis of GS.

Conclusions

We report here the first case of genetically confirmed GS manifested as normocalciuria in a Caucasian woman. Thus, our result does not confirm a role of sex hormones on the level of calciuria. Based on the results of normal Aldo concentration despite high renin level in our patient, we hypothesized that Aldo may be connecting with the level of urinary calcium excretion in patients with the GS.

Fanconi Syndrome Secondary to Sodium Valproate Therapy: Experience and Literature Review

BACKGROUND

Fanconi syndrome (FS) can be of primary or secondary origin. Some cases of FS secondary to the use of sodium valproate (VPA) have been described, mostly in children with severe psychomotor retardation who are fed by feeding device. The objetive of this study was to describe patients treated for this entity in our center, comparing them against the published literature.

METHODS

Descriptive study of our patients and those found in the literature. Epidemiologic and clinical data were collected.

RESULTS

We describe seven patients (three to 17 years old) with severe psychomotor retardation and undergoing treatment with VPA. Four presented pathologic fractures before the diagnosis of FS, and in three patients the diagnosis was reached due to abnormal laboratory findings. A review of the published cases was carried out and, including our sample, a total of 42 patients were studied: 51.3% were male, and the median age at diagnosis of FS was 6 years. Severe psychomotor retardation was found in 92.8% of patients, 78% carried a feeding device, and 77.5% received treatment with several antiepileptic drugs. The mean duration of VPA treatment was 5.7 years (range 2 to 7.5 years). Fifteen patients (37.5%) had bone complications. The resolution time of FS after discontinuation of drug therapy ranged from two to 19 months (median 4 months).

CONCLUSIONS

FS related to VPA is a rare complication, but it should be considered in patients with epilepsy, especially if they have severe psychomotor retardation, are users of feeding devices, and receive other antiepileptic treatments in addition to VPA.

A knock-in rat model unravels acute and chronic renal toxicity in glutaric aciduria type I

Glutaric aciduria type I (GA-I, OMIM # 231670) is an autosomal recessive inborn error of metabolism caused by deficiency of the mitochondrial enzyme glutaryl-CoA dehydrogenase (GCDH). The principal clinical manifestation in GA-I patients is striatal injury most often triggered by catabolic stress. Early diagnosis by newborn screening programs improved survival and reduced striatal damage in GA-I patients. However, the clinical phenotype is still evolving in the aging patient population. Evaluation of long-term outcome in GA-I patients recently identified glomerular filtration rate (GFR) decline with increasing age. We recently created the first knock-in rat model for GA-I harboring the mutation p.R411W (c.1231 C>T), corresponding to the most frequent GCDH human mutation p.R402W. In this study, we evaluated the effect of an acute metabolic stress in form of high lysine diet (HLD) on young Gcdh^ki/ki rats. We further studied the chronic effect of GCDH deficiency on kidney function in a longitudinal study on a cohort of Gcdh^ki/ki rats by repetitive ⁶⁸Ga-EDTA positron emission tomography (PET) renography, biochemical and histological analyses. In young Gcdh^ki/ki rats exposed to HLD, we observed a GFR decline and biochemical signs of a tubulopathy. Histological analyses revealed lipophilic vacuoles, thinning of apical brush border membranes and increased numbers of mitochondria in proximal tubular (PT) cells. HLD also altered OXPHOS activities and proteome in kidneys of Gcdh^ki/ki rats. In the longitudinal cohort, we showed a progressive GFR decline in Gcdh^ki/ki rats starting at young adult age and a decline of renal clearance. Histopathological analyses in aged Gcdh^ki/ki rats revealed tubular dilatation, protein accumulation in PT cells and mononuclear infiltrations. These observations confirm that GA-I leads to acute and chronic renal damage. This raises questions on indication for follow-up on kidney function in GA-I patients and possible therapeutic interventions to avoid renal damage.

Long-term renal outcome in methylmalonic acidemia in adolescents and adults

BACKGROUND

Chronic kidney disease (CKD) is one of the main long-term prognosis factors in methylmalonic acidemia (MMA), a rare disease of propionate catabolism. Our objective was to precisely address the clinical and biological characteristics of long-term CKD in MMA adolescent and adult patients.

PATIENTS AND METHODS

In this retrospective study, we included MMA patients older than 13 years who had not received kidney and/or liver transplantation. We explored tubular functions, with special attention to proximal tubular function. We measured glomerular filtration rate (mGFR) by iohexol clearance and compared it to estimated glomerular filtration rate (eGFR) by Schwartz formula and CKD-EPI.

RESULTS

Thirteen patients were included (M/F = 5/8). Median age was 24 years (13 to 32). Median mGFR was 57 mL/min/1.73 m2 (23.3 to 105 mL/min/1.73 m2). Ten out of 13 patients had mGFR below 90 mL/min/1.73 m2. No patient had significant glomerular proteinuria. No patient had complete Fanconi syndrome. Only one patient had biological signs suggestive of incomplete proximal tubulopathy. Four out of 13 patients had isolated potassium loss, related to a non-reabsorbable anion effect of urinary methylmalonate. Both Schwartz formula and CKD-EPI significantly overestimated GFR. Bias were respectively 16 ± 15 mL/min/1.73 m2 and 37 ± 22 mL/min/1.73 m2.

CONCLUSION

CKD is a common complication of the MMA. Usual equations overestimate GFR. Therefore, mGFR should be performed to inform therapeutic decisions such as dialysis and/or transplantation. Mild evidence of proximal tubular dysfunction was found in only one patient, suggesting that other mechanisms are involved.

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

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

Addison's disease associated with hypokalemia: a case report

BACKGROUND

Primary adrenal insufficiency (Addison's disease) is a rare medical condition usually associated with hyperkalemia or normokalemia. We report a rare case of Addison's disease, coexisting with hypokalemia, requiring treatment.

CASE PRESENTATION

In this case, a 42-year-old man was admitted to the intensive care unit with a history of loss of consciousness and severe hypoglycemia. His blood tests showed metabolic acidosis, low concentrations of cortisol 6 nmol/L (normal 68-327 nmol/L), and high plasma adrenocorticotropic hormone 253 pmol/L (normal 1.6-13.9 pmol/L), and he was diagnosed with primary adrenal insufficiency. Surprisingly, his serum potassium was low, 2.3 mmol/L (normal 3.5-5.1 mmol/L), requiring replacement over the course of his admission. Computed tomography scan of the adrenal glands showed features suggestive of unilateral adrenal tuberculosis. Investigations confirmed renal tubulopathy. The patient responded favorably to cortisol replacement, but never required fludrocortisone.

CONCLUSIONS

Coexistence of hypokalemia with Addison's disease is unusual. We recommend investigation of the cause of hypokalemia in its own right, if it occurs with primary adrenal insufficiency.

Etiopathogenic factors of urolithiasis

INTRODUCTION

Kidney stone disease affects 1 in 10 persons at least once per life-time worldwide, in 2% the disease is recurrent. For the individual stone disease can be painful and lead even to chronic kidney disease, while the costs for the health system and economy can be very high. Thus, factors causing stone disease need to be identified in order to prevent or reduce the incidence of disease.

AIM

This review will discuss major risk factors contributing to stone disease with special emphasis on genetic and dietary risk factors. RESULTS: Stone disease is multifactorial with a strong genetic component, gender-specific risks and prevalence, and a modifiable contribution of nutrition. The different factors contributing to the risk for developing stones are discussed.

DISCUSSION

Urolithiasis is a frequent disorder affecting almost 10% of the population with a high risk of recurrence. Treatment and prevention have to be tailored to the individual causes of disease and require an assessment of underlying predispositions and interacting modifiable environmental factors.

Chronic interstitial nephritis in agricultural communities (CINAC) and lysosomal tubulopathy: Is there a place for anti-oxidants?

Chronic Interstitial Nephritis in Agricultural Communities (CINAC) continues to attract controversy in the scientific community. It was previously known as Chronic Kidney Disease of Unknown Etiology (CKDu) and is not associated with the common aetiological factors such as diabetes. There is general acceptance that it is an environmentally induced disorder due to a combination of toxicities: heavy metals from food, fluoride in drinking water, hard water, heat stress and pesticides. The recent findings of a lysosomal inclusion body tubulopathy is of great interest to those attempting to find therapeutic agents to slow or eliminate its renal damage. The paper argues that despite these new findings, oxidative stress could play a key role and proposes that anti-oxidants such as Vitamin C and E be repurposed for treatment.

Persistently high urine glucose levels caused by familial renal glycosuria

Glycosuria generally occurs when the threshold for glucose reabsorption by the proximal renal tubule is exceeded or when reabsorption of filtered glucose is impaired. Although the discovery of glycosuria in a child will prompt screening for diabetes mellitus, it is also a sign of a rare tubulopathy called "familial renal glycosuria" (OMIM #233100). This tubulopathy is linked to a defect in the sodium-glucose co-transporter 2, encoded by the SLC5A2 gene. Here, we describe and discuss two pediatric cases in whom familial renal glycosuria was discovered fortuitously after the observation of persistently high urine glucose levels in the absence of hyperglycemia.

Recovery of Tenofovir-induced Nephrotoxicity following Switch from Tenofovir Disoproxil Fumarate to Tenofovir Alafenamide in Human Immunodeficiency Virus-Positive Patients

Background

Tenofovir disoproxil fumarate (TDF)-induced nephrotoxicity is related to high plasma tenofovir concentrations. Tenofovir alafenamide (TAF) is a tenofovir prodrug with 90% lower plasma tenofovir concentrations. The aim of this study was to evaluate changes in tenofovir-induced nephrotoxicity in Human Immunodeficiency Virus (HIV)-positive patients who switched from TDF to TAF.

Materials and Methods

We identified all HIV-positive patients who switched from elvitegravir/cobicistat/emtricitabine/TDF to elvitegravir/cobicistat/emtricitabine/TAF at a tertiary hospital. We assessed tubulopathy and renal dysfunction before TDF administration, at the time TAF was used following at least 3 months of TDF use, and 3 months after TAF administration. Tubulopathy was defined by the presence of at least three abnormalities in fractional excretion of phosphate, fractional excretion of uric acid, urinary β2-microglobulin, urinary N-acetyl-β-D-glucosaminidase, glucosuria or proteinuria. Renal dysfunction was defined as decreased by more than 25% in the estimated glomerular filtration rate (eGFR) relative to baseline.

Results

In 80 patients, the mean eGFR was 96.8 mL/min/1.73 m² before administration of TDF, 81.2 (P <0.001) at the time of change to TAF, 90.9 (P <0.001) after TAF administration. Renal dysfunction occurred in 19 patients (23.8%) after TDF use for a median 15 months, 11 (57.9%) of these patients recovered from renal dysfunction after TAF administration. Six patients (7.5%) had tubulopathy before TDF administration, 36 (45.0%) after TDF administration (P <0.001), 12 (15.0%) after TAF administration (P = 0.002).

Conclusion

Tenofovir-induced nephrotoxicity in HIV-positive patients receiving TDF was mostly reversible after changing to TAF. Thus, TAF-containing regimens can be administered safely to HIV-positive patients with tenofovir-induced nephrotoxicity.

Bartter and Gitelman syndromes: Questions of class

Bartter and Gitelman syndromes are rare inherited tubulopathies characterized by hypokalaemic, hypochloraemic metabolic alkalosis. They are caused by mutations in at least 7 genes involved in the reabsorption of sodium in the thick ascending limb (TAL) of the loop of Henle and/or the distal convoluted tubule (DCT). Different subtypes can be distinguished and various classifications have been proposed based on clinical symptoms and/or the underlying genetic cause. Yet, the clinical phenotype can show remarkable variability, leading to potential divergences between classifications. These problems mostly relate to uncertainties over the role of the basolateral chloride exit channel CLCNKB, expressed in both TAL and DCT and to what degree the closely related paralogue CLCNKA can compensate for the loss of CLCNKB function. Here, we review what is known about the physiology of the transport proteins involved in these disorders. We also review the various proposed classifications and explain why a gene-based classification constitutes a pragmatic solution.

Effect of nonsteroidal anti-inflammatory drugs in children with Bartter syndrome

BACKGROUND

Bartter syndrome (BS) is a salt-wasting tubulopathy with induced expression of cyclooxygenase-2 in the macula densa, leading to increased prostaglandin production and hyperreninemia. Nonsteroidal anti-inflammatory drugs (NSAIDs) are currently used in BS; however, there is limited information on the impact of NSAIDs at treatment initiation or the potential utility of plasma renin level to guide therapy in patients with BS.

METHODS

We included 19 patients with BS treated with NSAIDs between 1994 and 2016. We assessed serum levels of renin, aldosterone, electrolytes, calcium, phosphorus, vitamin D, and intact parathyroid hormone (iPTH) before and after treatment initiation. We also recorded modifications in sodium and potassium supplements and changes in urine calcium.

RESULTS

Median age at diagnosis was 0.9 months [IQR 0-6.9]. Seven patients had BS types 1 or 2, 12 had BS type 3 and two had no mutation identified. There was a trend towards a decrease in sodium chloride supplementation after initiation of NSAIDs. When defining response to treatment based on the normalization of plasma renin level, responders had a greater reduction in their electrolytes supplementation. NSAIDs treatment was associated with a reduction in urine calcium. Before treatment, half of the patients had elevated iPTH, but iPTH normalized following initiation of NSAIDs in all but one patient.

CONCLUSIONS

This study confirms that NSAIDs reduce urine wasting of sodium and calcium in patients with BS. Monitoring serum renin levels may be useful to identify the lowest effective dose of NSAIDs that optimizes reduction of urine electrolyte losses.

Aside from acute renal failure cases, are urinary markers of glomerular and tubular function useful in clinical practice?

The qualitative evaluation of proteinuria represents a crucial diagnostic step in clinical practice for the classification of renal diseases according to glomerular, tubulo-interstitial, mixed injury or related to monoclonal gammopathy. Combined with the quantitative evaluation, it also allows an assessment of the disease's severity and prognosis as well as the response to treatment. The development of the urine protein profile (UPP) combines specific urine protein assays on a urine spot analyzing glomerular protein markers such as albumin, transferrin and immunoglobulin G, and tubular markers such as alpha-1microglobulin and retinol binding protein, to generate a detailed quantitative and qualitative proteinuria assessment. This short overview proposes to illustrate the diagnostic and prognostic usefulness of UPP in different common clinical situations.

[Ifosphamide nephrotoxicity]

Ifosfamide is a cytotoxic drug usually used in malignant sarcomas. The nephrotoxicity of this agent has been described essentially among children, revealed by renal failure and proximal tubulopathy. We recently conducted a retrospective multicentre study, describing 34 adult patients admitted for ifosfamide nephrotoxicity. More than 80% of them presented with renal failure, diagnosed up to 48 months after ifosfamide administration. A Fanconi syndrome with hypophosphoremia, hypokaliemia, glucosuria and low-molecular weight proteinuria, was present in two third of all cases. Median estimated glomerular filtration rate was 31mL/min 1 month and 38mL/min 3 months after ifosfamide infusion, versus 67mL/min at baseline. Renal biopsy, performed in 14 of these patients, showed acute tubular necrosis with vacuolization of proximal tubular epithelial cells with marked nuclear modifications, whereas electron microscopy revealed major changes of mitochondrial structure inside those cells, suggesting a tenofovir-like mechanism of nephrotoxicity. After a median follow-up of 31 months, ten patients out of 34 reached stage 5 chronic kidney disease, requiring dialysis in five cases. Poor renal prognosis was associated with concomitant cisplatin use (P=0.02) and with older age at presentation (P=0.04). In conclusion, ifosfamide nephrotoxicity is often severe and irreversible, leading to proximal tubulopathy and sometimes-severe chronic kidney failure, that can be immediate or delayed, sometimes diagnosed months after chemotherapy completion.

Decreased expression of megalin and cubilin and altered mitochondrial activity in tenofovir nephrotoxicity

Tenofovir disoproxil fumarate (TDF) is a commonly used antiretroviral drug for HIV, rarely causing Fanconi syndrome and acute kidney injury. We retrospectively analyzed the clinico pathological presentation of 20 cases of tenofovir-induced tubulopathy, and investigated the renal expression of the megalin and cubilin proteins, as well as the mitochondrial respiratory chain activity. Estimated glomerular filtration rate (eGFR) before TDF exposure was 92 ml/min/1.73m², decreasing to 27.5 ml/min/1.73m² at the time of biopsy, with 30% of patients requiring renal replacement therapy. Proximal tubular expression of megalin and cubilin was altered in 19 and 18 cases, respectively, whereas it was preserved in patients exposed to TDF without proximal tubular dysfunction and in HIV-negative patients with acute tubular necrosis. Loss of megalin/cubilin was correlated with low eGFR and high urine retinol binding protein at the time of biopsy, low eGFR at last follow-up, and was more severe in patients with multifactorial toxicity. Patients with additional nephrotoxic conditions promoting tenofovir accumulation showed a lower eGFR at presentation and at last follow-up, and more severe lesions of acute tubular necrosis, than those with isolated tenofovir toxicity. Altered mitochondrial COX activity in proximal tubules was observed and may be an early cellular alteration in tenofovir nephrotoxicity. In conclusion, altered megalin/cubilin expression represents a distinctive feature in tenofovir-induced tubulopathy, and its severity is correlated with urine retinol binding protein loss and is associated with a poor renal prognosis. Concomitant exposure to other nephrotoxic conditions severely impacts the renal presentation and outcome.

Glomerular and Tubular Functions in Children and Adults with Transfusion-Dependent Thalassemia

This study aimed at assessing renal functions in patients with transfusion-dependent thalassemia (TDT). Fifty patients and 30 controls were enrolled in this prospective study. Serum levels of electrolytes and albumin were measured by a spectrophotometer. Serum levels of cystatin-C and urinary levels of β2-microglobulin were measured by nephelometric method. Thirty-eight patients were receiving deferasirox and 8 were on deferiprone. Serum electrolytes and albumin levels of the patients were found to be within normal ranges. Urinary β2-microglobulin and serum cystatin-C levels were significantly higher in patients than controls. They did not significantly differ between the subgroup of patients on deferiprone and the control group, whereas they were found to be higher in patients using deferasirox compared to controls. Urinary β2-microglobulin levels significantly increased in patients who were receiving high-dose deferasirox compared to those who were receiving a daily dose of 15-20 mg/kg or controls. Subclinical renal injury may be present in TDT patients.

Treatment-limiting renal tubulopathy in patients treated with tenofovir disoproxil fumarate

OBJECTIVES

Tenofovir disoproxil fumarate (TDF) is widely used in the treatment or prevention of HIV and hepatitis B infection. TDF may cause renal tubulopathy in a small proportion of recipients. We aimed to study the risk factors for developing severe renal tubulopathy.

METHODS

We conducted an observational cohort study with retrospective identification of cases of treatment-limiting tubulopathy during TDF exposure. We used multivariate Poisson regression analysis to identify risk factors for tubulopathy, and mixed effects models to analyse adjusted estimated glomerular filtration rate (eGFR) slopes.

RESULTS

Between October 2002 and June 2013, 60 (0.4%) of 15,983 patients who had received TDF developed tubulopathy after a median exposure of 44.1 (IQR 20.4, 64.4) months. Tubulopathy cases were predominantly male (92%), of white ethnicity (93%), and exposed to antiretroviral regimens that contained boosted protease inhibitors (PI, 90%). In multivariate analysis, age, ethnicity, CD4 cell count and use of didanosine or PI were significantly associated with tubulopathy. Tubulopathy cases experienced significantly greater eGFR decline while receiving TDF than the comparator group (-6.60 [-7.70, -5.50] vs. -0.34 [-0.43, -0.26] mL/min/1.73 m²/year, p < 0.0001).

CONCLUSIONS

Older age, white ethnicity, immunodeficiency and co-administration of ddI and PI were risk factors for tubulopathy in patients who received TDF-containing antiretroviral therapy. The presence of rapid eGFR decline identified TDF recipients at increased risk of tubulopathy.

Gitelman's syndrome as a cause of poorly controlled hypokalemia

Gitelman's syndrome is a rare autosomal recessive tubulopathy caused by a defect of the thiazide-sensitive sodium chloride co-transporter at the distal tubule, leading to hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria and low-to-normal blood pressure. Clinical features include transient periods of muscle weakness and tetany, dizziness, abdominal pains and constipation. Patients can also present with convulsions due to severe metabolic alkalosis or hypomagnesemia. Therefore, early recognition and treatment are important. Diagnosis of Gitelman's syndrome is usually made incidentally during adolescence or early adulthood based on clinical and biochemical findings. In this paper we present the case of a 23-year-old female patient referred to our nephrology department for severe hypokalemia. Complementary evaluation revealed hypokalemia, hypomagnesemia, metabolic alkalosis, increased chloride and sodium urinary excretion and reduced urinary calcium excretion with normal renal function. A diagnosis of Gitelman syndrome was established. Treatment included magnesium and potassium salts and potassium saving diuretics. In general, the long-term prognosis of Gitelman's syndrome is good if the patient adhere with the treatment.

New SLC12A3 disease causative mutation of Gitelman’s syndrome

Gitelman’s syndrome (GS) is a salt-losing tubulopathy with an autosomal recessive inheritance caused by mutations of SLC12A3, which encodes for the thiazide-sensitive NaCl cotransporter. In this study we report a new mutation of SLC12A3 found in two brothers affected by GS. Hypokalemia, hypocalciuria and hyper-reninemia were present in both patients while hypomagnesemia was detected only in one. Both patients are compound heterozygotes carrying one well known GS associated mutation (c.2581 C > T) and a new one (c.283delC) in SLC12A3 gene. The new mutation results in a possible frame-shift with a premature stop-codon (pGln95ArgfsX19). The parents of the patients, heterozygous carriers of the mutations found in SLC12A3, have no disease associated phenotype. Therefore, the new mutation is causative of GS.

[Tenofovir nephrotoxicity]

Tenofovir is currently the only commercially available nucleotidic reverse-transcriptase inhibitor of human immunodeficiency virus (HIV). It is overall very well tolerated and is prescribed to millions of patients-without any specific monitoring in developing countries. However a significant nephrotoxicity has been described. Acute nephrotoxicity is well characterized. Tenofovir is excreted in urine by proximal tubular epithelial cells. In case of cytoplasmic accumulation, tenofovir inhibits mitochondrial DNA polymerase γ, which causes a dysfunction of the respiratory chain, and in turn an alteration of the energy-deprived cells. Fanconi syndrome is the clinical expression of tenofovir acute toxicity, with sometimes an associated acute kidney failure. These abnormalities are usually reversible, at least partially, when tenofovir is discontinued. Tenofovir chronic toxicity has been debated but seems now well established by several cohort studies, even though it pathophysiology has yet to be understood. It manifests as an accelerated glomerular filtration rate decline in treated patients with no other renal abnormalities. The identification of this chronic toxicity was probably blurred by multiple cofactors, usually excluded from clinical trials. Simple measures such as dose adaptation to kidney function, identification of risk factors, and plasmatic tenofovir concentration monitoring can help decrease the risk of nephrotoxicity.

Tenofovir substitution in Namibia based on an analysis of the antiretroviral dispensing database

Objectives

In the management of HIV infection, tenofovir is preferred to its predecessors – zidovudine and stavudine – in the antiretroviral therapy (ART) nucleoside backbone. Tenofovir’s (TDF) preference is based on its safety profile. Nevertheless, TDF causes adverse reactions, some of which warrant its substitution for patients. The rate of TDF-substitution is suggestive of the rate of occurrence of TDF-related adverse reactions. However, the rate of substitution of TDF with another nucleoside reverse transcriptase inhibitor (NRTI) in Namibia was unknown. The objective of this review was to measure the rate of TDF’s substitution for the period of January 1, 2008 to November 30, 2011, and to compare the gender difference in the rates of TDF’s substitution.

Methods

We accessed antiretroviral medicine dispensing records from the national antiretroviral dispensing database (NDB). We selected patients who were started on a TDF-containing conventional ART regimen – 2NRTI+1NNRT. We used the initial and current ART regimens to identify records of TDF’s substitution with another NRTI.

Results

A total of 84,741 patients were initiated on ART (Jan-1-2008 to Nov-30-2011). A total of 52,612 patient-records were excluded from the analysis because they did not meet the criteria for inclusion. Of the 32,129 included records, 59.4% (n=19 096) and 40.6% (n=13 033) were for female and male patients, respectively. Of these, 1.2% (n=380) of the patients had their TDF substituted with another NRTI. Of the females and males, respectively, 1.1% (95% CI: 0.9-1.3; n=210) and 1.3% (95% CI: 1.1-1.5; n=170) had TDF substituted with another NRTI. No gender difference was observed (p-value = 0.11).

Conclusion

The percentage of patients for whom TDF was substituted with another NRTI, possibly due to TDF-related adverse reactions, was within the current published limits. However, 1.2% is likely not a true representation of the percentage of patients who experience adverse events because some patients could have been maintained on TDF even in the presence of adverse events. Further investigation is required to determine the clinical reasons for TDF’s withdrawal.

Mislocalization of K+ channels causes the renal salt wasting in EAST/SeSAME syndrome

The Kir4.1/Kir5.1 channel mediates basolateral K(+) recycling in renal distal tubules; this process is critical for Na(+) reabsorption at the tubules. Mutations in Kir4.1 are associated with EAST/SeSAME syndrome, a genetic disorder characterized by renal salt wasting. In this study, we found that MAGI-1 anchors Kir4.1 channels (Kir4.1 homomer and Kir4.1/Kir5.1 heteromer) and contributes to basolateral K(+) recycling. The Kir4.1 A167V mutation associated with EAST/SeSAME syndrome caused mistrafficking of the mutant channels and inhibited their expression on the basolateral surface of tubular cells. These findings suggest mislocalization of the Kir4.1 channels contributes to renal salt wasting.