Recurrent 2,8-dihydroxyadenine nephropathy: a rare but preventable cause of renal allograft failure

Discovery of 2,8-dihydroxyadenine in HUA patients with uroliths and biomarkers for its associated nephropathy

Currently, it is acknowledged that gout is caused by uric acid (UA). However, some studies have revealed no correlation between gout and UA levels, and growing evidence suggests that 2,8-dihydroxyadenine (2,8-DHA), whose structural formula is similar to UA but is less soluble, may induce gout. Hence, we hypothesized that uroliths from hyperuricemia (HUA) patients, which is closely associated with gout, may contain 2,8-DHA. In this study, 2,8-DHA in uroliths and serum of HUA patients were determined using HPLC. Moreover, bioinformatics was used to investigate the pathogenic mechanisms of 2,8-DHA nephropathy. Subsequently, a mouse model of 2,8-DHA nephropathy established by the gavage administration of adenine, as well as a model of injured HK-2 cells induced by 2,8-DHA were used to explore the pathogenesis of 2,8-DHA nephropathy. Interestingly, 2,8-DHA could readily deposit in the cortex of the renal tubules, and was found in the majority of these HUA patients. Additionally, the differentially expressed genes between 2,8-DHA nephropathy mice and control mice were found to be involved in inflammatory reactions. Importantly, CCL2 and IL-1β genes had the maximum degree, closeness, and betweenness centrality scores. The expressions of CCL2 and IL-1β genes were significantly increased in the serum of 24 HUA patients with uroliths, indicating that they may be significant factors for 2,8-DHA nephropathy. Further analysis illustrated that oxidative damage and inflammation were the crucial processes of 2,8-DHA renal injury, and CCL2 and IL-1β genes were verified to be essential biomarkers for 2,8-DHA nephropathy. These findings revealed further insights into 2,8-DHA nephropathy, and provided new ideas for its diagnosis and treatment.

A case of 2,8-DHA crystalline nephropathy caused by adenine phosphoribosyltransferase deficiency: diagnosis and treatment

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder that leads to the accumulation of poorly soluble 2,8-dihydroxyadenine (DHA) in the kidneys, resulting in a variety of renal presentations including nephrolithiasis, acute kidney injury, and chronic kidney disease (CKD) caused by crystal nephropathy. Here, we report a case of a 43-year-old man with 2,8-DHA crystalline nephropathy caused by APRT deficiency strongly suspected by renal biopsy results and definitively diagnosed by a urine gas chromatography-mass spectrometry (GC/MS)-based plasma metabolomic assessment. This case represents the importance of awareness and recognition of the signs and symptoms of this rare condition and its progression to CKD, which can be prevented by the early administration of xanthine oxidoreductase inhibitors.

A deficiência de adenina fosforibosiltransferase leva à disfunção do aloenxerto renal em receptores de transplante renal: uma revisão sistemática

Resumo Antecedentes: A deficiência de adenina fosforibosiltransferase (APRT) tem grandes implicações na sobrevida do enxerto em pacientes transplantados renais. Esta revisão sistemática investigou o padrão diagnóstico, a abordagem de tratamento e os desfechos do transplante renal entre pacientes transplantados renais com deficiência de adenina fosforibosiltransferase. Material e métodos: Os artigos que relatam sobre a enzima APRT e a disfunção do aloenxerto renal foram recuperados do PubMed/Medline, ScienceDirect, Biblioteca Cochrane e bancos de dados do Google Acadêmico. Utilizou-se a análise descritiva para extrair inferências. Resultados: Foram incluídos participantes que receberam 39 enxertos, a maioria dos quais provenientes de doadores vivos seguidos por doadores falecidos e doadores cadáveres. Foi relatado tempo de sobrevida do enxerto superior a 6 meses em 23 (76,7%) pacientes, enquanto outros 7 (23,3%) pacientes tiveram tempo de sobrevida do enxerto inferior a 6 meses. Apenas 4 (13,3%) pacientes apresentaram deficiência de APRT antes do transplante. Após acompanhamento, um terço dos pacientes, 10 (33,3%) apresentaram função do enxerto estável, 1 paciente teve perda do aloenxerto, 8 (26,6%) pacientes apresentaram função retardada do enxerto, enquanto os 11 (36,6%) pacientes restantes tiveram disfunção crônica do enxerto renal. Conclusões: A deficiência de APRT é uma causa subestimada e reversível de nefropatia cristalina que leva à disfunção do aloenxerto renal ou à perda total do aloenxerto. Os resultados deste estudo pedem a inclusão desta condição no diagnóstico diferencial de nefropatia cristalina, mesmo na ausência de um histórico de nefrolitíase.

Adenine phosphoribosyl transferase deficiency leads to renal allograft dysfunction in kidney transplant recipients: a systematic review

Background:

Adenine phosphoribosyl transferase (APRT) deficiency has great implications on graft survival in kidney transplant patients. This systematic review investigated the diagnostic pattern, treatment approach, and kidney transplant outcomes among kidney transplant patients with adenine phosphoribosyl transferase deficiency.

Material and methods:

Articles reporting the APRT enzyme deficiency and kidney allograft dysfunction were retrieved from PubMed/Medline, ScienceDirect, Cochrane library and Google scholar databases. Descriptive analysis was used to draw inferences.

Results:

The results from 20 selected studies covering 30 patients receiving 39 grafts had an average age of 46.37 years are presented. Graft survival time of more than 6 months was reported in 23 (76.7%) patients, while other 7 (23.3%) patients had graft survival time of less than 6 months. Only 4 (13.3%) patients had APRT deficiency before transplantation. After follow-up, one-third of the patients 10 (33.3%) had stable graft function, 1 patient had allograft loss, 8 (26.6%) patients had delayed graft function while the remaining 11 (36.6%) patients had chronic kidney graft dysfunction.

Conclusions:

APRT deficiency is an under-recognized, treatable condition that causes reversible crystalline nephropathy, leading to loss of allograft or allograft dysfunction. The study results showed that inclusion of genetic determination of APRT deficiency in the differential diagnosis of crystalline nephropathy, even in the absence of a history of nephrolithiasis, can improve renal outcomes and may improve allograft survival.

Recurrence of 2,8-dihydroxyadenine Crystalline Nephropathy in a Kidney Transplant Recipient: A Case Report and Literature Review

We herein report the case of a kidney transplant patient with recurrence of obstructive nephropathy that was not diagnosed as adenine phosphoribosyltransferase (APRT) deficiency until gene testing identified a pathogenic homozygous variant three years after renal transplantation. Subsequently, the patient was treated with allopurinol, and the allograft function increased progressively to normal. In addition, 20 cases of APRT deficiency in renal transplant recipients were also reviewed. We hope this case increases awareness of APRT deficiency in repeated obstructive nephropathy post-transplantation, which is a treatable disease for which the misdiagnosis or delayed diagnosis should be avoided.

Acute Kidney Injury (AKI) before and after Kidney Transplantation: Causes, Medical Approach, and Implications for the Long-Term Outcomes

Acute kidney injury (AKI) is a common finding in kidney donors and recipients. AKI in kidney donor, which increases the risk of delayed graft function (DGF), may not by itself jeopardize the short- and long-term outcome of transplantation. However, some forms of AKI may induce graft rejection, fibrosis, and eventually graft dysfunction. Therefore, various strategies have been proposed to identify conditions at highest risk of AKI-induced DGF, that can be treated by targeting the donor, the recipient, or even the graft itself with the use of perfusion machines. AKI that occurs early post-transplant after a period of initial recovery of graft function may reflect serious and often occult systemic complications that may require prompt intervention to prevent graft loss. AKI that develops long after transplantation is often related to nephrotoxic drug reactions. In symptomatic patients, AKI is usually associated with various systemic medical complications and could represent a risk of mortality. Electronic systems have been developed to alert transplant physicians that AKI has occurred in a transplant recipient during long-term outpatient follow-up. Herein, we will review most recent understandings of pathophysiology, diagnosis, therapeutic approach, and short- and long-term consequences of AKI occurring in both the donor and in the kidney transplant recipient.

Recurrent DHA nephropathy in renal allograft-revisiting clinicopathological aspects of a rare entity

Background

Adenine phosphoribosyltransferase (APRT) enzyme deficiency is a rare autosomal recessive disorder of purine metabolism affecting mainly the kidneys. It can present at any age with varying degrees of acute and chronic renal damage. Though xanthine dehydrogenase inhibitors offer effective control over the disease process, delay in diagnosis and treatment often lead to compromised function of native and even graft kidneys.

Methods

We have done a retrospective search of records of renal biopsies reported at our center during the 5-year period from 2014 to 2018 to identify biopsies with 2,8-dihydroxyadenine crystal deposits. The demographic, clinical, and histopathological findings in these cases were studied and reviewed in the light of available literature.

Results

Of 9059 renal biopsies received during the study period, 3 cases had the rare 2,8- dihydroxyadenine (DHA) crystals. All of them were diagnosed for the first time on allograft biopsies.

Conclusion

A high index of clinical suspicion together with the characteristic microscopic appearance of crystals on renal biopsy and urine microscopy can clinch the diagnosis of this rare disease. Hence, improving awareness about this entity among clinicians and pathologists is extremely important.

Are conventional stone analysis techniques reliable for the identification of 2,8-dihydroxyadenine kidney stones? A case series

We have recently encountered patients incorrectly diagnosed with adenine phosphoribosyltransferase (APRT) deficiency due to misidentification of kidney stones as 2,8-dihydroxyadenine (DHA) stones. The objective of this study was to examine the accuracy of stone analysis for identification of DHA. Medical records of patients referred to the APRT Deficiency Research Program of the Rare Kidney Stone Consortium in 2010-2018 with a diagnosis of APRT deficiency based on kidney stone analysis were reviewed. The diagnosis was verified by measurement of APRT enzyme activity or genetic testing. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra of pure crystalline DHA and a kidney stone obtained from one of the confirmed APRT deficiency cases were generated. The ATR-FTIR spectrum of the kidney stone matched the crystalline DHA spectrum and was used for comparison with available infrared spectra of stone samples from the patients. Of 17 patients referred, 14 had sufficient data available to be included in the study. In all 14 cases, the stone analysis had been performed by FTIR spectroscopy. The diagnosis of APRT deficiency was confirmed in seven cases and rejected in the remaining seven cases. Comparison of the ATR-FTIR spectrum of the DHA stone with the FTIR spectra from three patients who did not have APRT deficiency showed no indication of DHA as a stone component. Misidentification of DHA as a kidney stone component by clinical laboratories appears common among patients referred to our program. Since current clinical protocols used to interpret infrared spectra for stone analysis cannot be considered reliable for the identification of DHA stones, the diagnosis of APRT deficiency must be confirmed by other methods.

Cellular and Molecular Mechanisms of Kidney Injury in 2,8-Dihydroxyadenine Nephropathy

BACKGROUND

Hereditary deficiency of adenine phosphoribosyltransferase causes 2,8-dihydroxyadenine (2,8-DHA) nephropathy, a rare condition characterized by formation of 2,8-DHA crystals within renal tubules. Clinical relevance of rodent models of 2,8-DHA crystal nephropathy induced by excessive adenine intake is unknown.

METHODS

Using animal models and patient kidney biopsies, we assessed the pathogenic sequelae of 2,8-DHA crystal-induced kidney damage. We also used knockout mice to investigate the role of TNF receptors 1 and 2 (TNFR1 and TNFR2), CD44, or alpha2-HS glycoprotein (AHSG), all of which are involved in the pathogenesis of other types of crystal-induced nephropathies.

RESULTS

Adenine-enriched diet in mice induced 2,8-DHA nephropathy, leading to progressive kidney disease, characterized by crystal deposits, tubular injury, inflammation, and fibrosis. Kidney injury depended on crystal size. The smallest crystals were endocytosed by tubular epithelial cells. Crystals of variable size were excreted in urine. Large crystals obstructed whole tubules. Medium-sized crystals induced a particular reparative process that we term extratubulation. In this process, tubular cells, in coordination with macrophages, overgrew and translocated crystals into the interstitium, restoring the tubular luminal patency; this was followed by degradation of interstitial crystals by granulomatous inflammation. Patients with adenine phosphoribosyltransferase deficiency showed similar histopathological findings regarding crystal morphology, crystal clearance, and renal injury. In mice, deletion of Tnfr1 significantly reduced tubular CD44 and annexin two expression, as well as inflammation, thereby ameliorating the disease course. In contrast, genetic deletion of Tnfr2, Cd44, or Ahsg had no effect on the manifestations of 2,8-DHA nephropathy.

CONCLUSIONS

Rodent models of the cellular and molecular mechanisms of 2,8-DHA nephropathy and crystal clearance have clinical relevance and offer insight into potential future targets for therapeutic interventions.

Kidney Transplant Outcomes in Patients With Adenine Phosphoribosyltransferase Deficiency

BACKGROUND

Adenine phosphoribosyltransferase (APRT) deficiency is a rare, hereditary cause of kidney stones and chronic kidney disease (CKD) which is characterized by 2,8-dihydroxyadenine renal parenchymal crystal deposition. The aim of this study was to examine outcomes of kidney transplantation in APRT deficiency patients.

METHODS

Included were 13 patients in the APRT Deficiency Registry of the Rare Kidney Stone Consortium, 2 from Westmead Hospital in Sydney, Australia, and 2 from Necker Hospital in Paris, France. The CKD-EPI and CKiD equations were used to calculate glomerular filtration rate estimates. Allograft survival was analyzed employing the Kaplan-Meier method. The Wilcoxon-Mann-Whitney test was used to compare alllograft outcomes according to xanthine oxidoreductase (XOR) inhibitor treatment status at transplantation.

RESULTS

Seventeen patients (9 females) received 22 kidney transplants. Age at first transplantation was 47.2 (14.9-67.0) years. Ten patients received XOR inhibitor therapy pretransplant (11 allografts), while 8 patients did not receive such treatment before transplantation (11 allografts). Two-year allograft survival was 91% and 55% in the 2 groups, respectively (P = 0.16). The median (range) estimated glomerular filtration rate at 2 years posttransplant was 61.3 (24.0-90.0) mL/min/1.73 m when XOR inhibitor therapy was initiated before transplantation, and 16.2 (10.0-39.0) mL/min/1.73 m (P = 0.009) when such treatment was not administered pretransplant.

CONCLUSIONS

Kidney allograft outcomes are good in APRT deficiency patients beginning XOR inhibitor therapy pretransplant. Delay in such treatment is a major cause of premature graft loss in these patients. Increased awareness among clinicians is imperative, promoting early diagnosis of APRT deficiency and pharmacotherapy initiation before kidney transplantation.

Long-term renal outcomes of APRT deficiency presenting in childhood

BACKGROUND

Adenine phosphoribosyltransferase (APRT) deficiency is a hereditary purine metabolism disorder that causes kidney stones and chronic kidney disease (CKD). The purpose of this study was to examine the course of APRT deficiency in patients who presented in childhood.

METHODS

The disease course of 21 (35%) patients in the APRT Deficiency Registry of the Rare Kidney Stone Consortium, who presented with manifestations of APRT deficiency and/or were diagnosed with the disorder before the age of 18 years, was studied. The effect of pharmacotherapy on renal manifestations and outcomes was thoroughly assessed.

RESULTS

Fourteen children were placed on allopurinol, 100 (25-200) mg/day, at the age of 2.6 (0.6-16.5) years. Six of these patients had experienced kidney stone events and three had developed acute kidney injury (AKI) prior to allopurinol treatment. During 18.9 (1.7-31.5) years of pharmacotherapy, stones occurred in two patients and AKI in three. Six adult patients started allopurinol treatment, 200 (100-300) mg/day, at age 29.8 (20.5-42.4) years. Five of these patients had experienced 28 stone episodes and AKI had occurred in two. Stone recurrence occurred in four patients and AKI in two during 11.2 (4.2-19.6) years of allopurinol therapy. Lack of adherence and insufficient dosing contributed to stone recurrence and AKI during pharmacotherapy. At latest follow-up, estimated glomerular filtration rate (eGFR) was 114 (70-163) and 62 (10-103) mL/min/1.73 m² in those who initiated treatment as children and adults, respectively. All three patients with CKD stages 3-5 at the last follow-up were adults when pharmacotherapy was initiated.

CONCLUSION

Timely diagnosis and treatment of APRT deficiency decreases renal complications and preserves kidney function.

APRT deficiency: the need for early diagnosis

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder which leads to accumulation of poorly soluble 2,8-dihydroxyadenine in kidneys resulting in nephrolithiasis as well as chronic kidney disease from crystal nephropathy. This report describes a 55-year-old previously fit man who presented with shortness of breath and the investigative pathway that eventually led to a diagnosis of APRT deficiency. Early diagnosis has aided in timely institution of allopurinol, thereby improving his renal function and possibility of weaning off renal replacement therapy. Genetic testing has enabled early identification of other family members at risk and prevention of renal failure by commencing xanthine oxidoreductase (XOR) inhibitors. The issues surrounding kidney donation by a member of this family are also discussed. This case represents the importance of awareness and recognition of the signs and symptoms of this rare condition, complications of which can be easily prevented by early institution of XOR inhibitor therapy.

Dihydroxyadenine crystal-induced nephropathy presenting with rapidly progressive renal failure

Adenine phosphoribosyltransferase enzyme deficiency is a rare, autosomal recessive disorder. It is a disease limited to the renal system and usually presents with urolithiasis. Herein, we report a young female with dihydroxyadenine (DHA) crystal-induced nephropathy presenting with rapidly progressive renal failure. DHA crystals can be easily diagnosed by their pathognomic color and shape in urine and biopsy specimens. A high index of clinical suspicion helps in the early diagnosis of this potentially treatable renal disease.

Combining multi-dimensional data to identify a key signature (gene and miRNA) of cisplatin-resistant gastric cancer

Gastric cancer (GC) is one of the most lethal malignant tumors; the resistance of this type of tumor is the main source of GC treatment failure. In this study, we used bioinformatics analysis to verify differences in resistant GCs and identify an effective method for reversing drug resistance in GC. Microarray data [gene and microRNA (miRNA)] were analyzed using GEO2R software, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were applied to further enrich the genetic data. miRNA-gene interactions were determined using Cytoscape (v.3.5.1). Online software was used to analyze protein interactions and predict network structure. The Cancer Genome Atlas (TCGA) database was used to verify the expression levels of genes in GC resistance. miR-604 expression levels were verified by real-time PCR in GC cell lines. We screened 3981 GC resistance-associated genes and 244 miRNAs using bioinformatics methods. Six hub genes were identified and verified in the TCGA database, including five up-regulated genes, POLR2L, POLR2C, POLR2F, APRT, and LMAN2, and a down-regulated gene, NFKB2. The up-regulated genes POLR2L, POLR2C, APRT, and LMAN2 interact with miR-604; therefore, we focused on miR-604, which has low expression in drug-resistant GC. The results of this study indicate that through bioinformatics technologies, we have determined the hub genes and hub miRNAs related to drug resistance in GC. Among them, miR-604 could become a new indicator in the diagnosis of drug-resistant GC and may be used to investigate the pathogenesis of resistance in GC.

Structural Insights into the Forward and Reverse Enzymatic Reactions in Human Adenine Phosphoribosyltransferase

Phosphoribosyltransferases catalyze the displacement of a PRPP α-1'-pyrophosphate to a nitrogen-containing nucleobase. How they control the balance of substrates/products binding and activities is poorly understood. Here, we investigated the human adenine phosphoribosyltransferase (hAPRT) that produces AMP in the purine salvage pathway. We show that a single oxygen atom from the Tyr105 side chain is responsible for selecting the active conformation of the 12 amino acid long catalytic loop. Using in vitro, cellular, and in crystallo approaches, we demonstrated that Tyr105 is key for the fine-tuning of the kinetic activity efficiencies of the forward and reverse reactions. Together, our results reveal an evolutionary pressure on the strictly conserved Tyr105 and on the dynamic motion of the flexible loop in phosphoribosyltransferases that is essential for purine biosynthesis in cells. These data also provide the framework for designing novel adenine derivatives that could modulate, through hAPRT, diseases-involved cellular pathways.

Comparison of the effect of allopurinol and febuxostat on urinary 2,8-dihydroxyadenine excretion in patients with Adenine phosphoribosyltransferase deficiency (APRTd): A clinical trial

INTRODUCTION

Adenine phosphoribosyltransferase (APRT) deficiency is a rare, but significant, cause of kidney stones and progressive chronic kidney disease. The optimal treatment has not been established. The purpose of this pilot study was to compare the effect of the xanthine oxidoreductase inhibitors allopurinol and febuxostat on urinary 2,8-dihydroxyadenine (DHA) excretion in APRT deficiency patients.

MATERIALS AND METHODS

Patients listed in the APRT Deficiency Registry of the Rare Kidney Stone Consortium, currently receiving allopurinol therapy, were invited to participate. The trial endpoint was the 24-h urinary DHA excretion following treatment with allopurinol (400mg/day) and febuxostat (80mg/day). Urinary DHA was measured using a novel ultra-performance liquid chromatography - electrospray tandem mass spectrometry assay.

RESULTS

Eight of the 10 patients invited completed the study. The median (range) 24-h urinary DHA excretion was 116 (75-289) mg at baseline, and 45 (13-112) mg after 14days of allopurinol therapy (P=0.036). At the end of the febuxostat treatment period, 4 patients had urinary DHA below detectable limits (<20ng/mL) compared with none of the participants following allopurinol treatment (P=0.036). The other 4 participants had a median 24-h urinary DHA excretion of 13.2 (10.0-13.4) mg at the completion of febuxostat therapy (P=0.036).

CONCLUSION

Urinary DHA excretion in APRT deficiency patients decreased with conventional doses of both allopurinol and febuxostat. Febuxostat was, however, significantly more efficacious than allopurinol in reducing DHA excretion in the prescribed doses. This finding, which may translate into improved outcomes of patients with APRT deficiency, should be confirmed in a larger sample.

In-silico gene essentiality analysis of polyamine biosynthesis reveals APRT as a potential target in cancer

Constraint-based modeling for genome-scale metabolic networks has emerged in the last years as a promising approach to elucidate drug targets in cancer. Beyond the canonical biosynthetic routes to produce biomass, it is of key importance to focus on metabolic routes that sustain the proliferative capacity through the regulation of other biological means in order to improve in-silico gene essentiality analyses. Polyamines are polycations with central roles in cancer cell proliferation, through the regulation of transcription and translation among other things, but are typically neglected in in silico cancer metabolic models. In this study, we analysed essential genes for the biosynthesis of polyamines. Our analysis corroborates the importance of previously known regulators of the pathway, such as Adenosylmethionine Decarboxylase 1 (AMD1) and uncovers novel enzymes predicted to be relevant for polyamine homeostasis. We focused on Adenine Phosphoribosyltransferase (APRT) and demonstrated the detrimental consequence of APRT gene silencing on different leukaemia cell lines. Our results highlight the importance of revisiting the metabolic models used for in-silico gene essentiality analyses in order to maximize the potential for drug target identification in cancer.

Early Recognition and Management of Rare Kidney Stone Disorders

Kidney stones, especially those that present in childhood/adolescence, may be due to rare inherited disorders such as cystinuria. Early recognition and prompt treatment can help reduce or even prevent the serious long-term complications of these rare stone disorders.

Febuxostat for the Prevention of Recurrent 2,8-dihydroxyadenine Nephropathy due to Adenine Phosphoribosyltransferase Deficiency Following Kidney Transplantation

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder that results in irreversible renal damage due to 2,8-dihydroxyadenine (DHA) nephropathy. A 28-year-old man underwent living-related kidney transplantation for chronic kidney disease of unknown etiology. Numerous spherical brownish crystals observed in his urinary sediment on postoperative day 3 and were observed within the tubular lumen of renal allograft biopsy specimens on postoperative day 7. After a genetic diagnosis, febuxostat treatment was started on postoperative day 7, with the dosage gradually increased to 80 mg/day until complete the disappearance of 2,8-DHA crystals. Febuxostat prevented secondary 2,8-DHA nephropathy after kidney transplantation.

A label-free approach by infrared spectroscopic imaging for interrogating the biochemistry of diabetic nephropathy progression

Routine histology, the current gold standard, involves staining for specific biomolecules. However, untapped biochemical information in tissue can be gathered using biochemical imaging. Infrared spectroscopy is an emerging modality that allows label-free chemical imaging to derive biochemical information (such as protein, lipids, DNA, collagen) from tissues. Here we employed this technology in order to better predict the development of diabetic nephropathy. Using human primary kidney biopsies or nephrectomies, we obtained tissue from 4 histologically normal kidneys, 4 histologically normal kidneys from diabetic subjects, and 5 kidneys with evidence of diabetic nephropathy. A biochemical signature of diabetic nephropathy was derived that enabled prediction of nephropathy based on the ratio of only 2 spectral frequencies. Nonetheless, using the entire spectrum of biochemical information, we were able to detect renal disease with near-perfect accuracy. Additionally, study of sequential protocol biopsies from 3 transplanted kidneys showed biochemical changes even prior to clinical manifestation of diabetic nephropathy. Thus, infrared imaging can identify critical biochemical alterations that precede morphologic changes, potentially allowing for earlier intervention.

Kidney Disease in Adenine Phosphoribosyltransferase Deficiency

BACKGROUND

Adenine phosphoribosyltransferase (APRT) deficiency is a purine metabolism disorder causing kidney stones and chronic kidney disease (CKD). The course of nephrolithiasis and CKD has not been well characterized. The objective of this study was to examine long-term kidney outcomes in patients with APRT deficiency.

STUDY DESIGN

An observational cohort study.

SETTING & PARTICIPANTS

All patients enrolled in the APRT Deficiency Registry of the Rare Kidney Stone Consortium.

OUTCOMES

Kidney stones, acute kidney injury (AKI), stage of CKD, end-stage renal disease, estimated glomerular filtration rate (eGFR), and changes in eGFR.

MEASUREMENTS

Serum creatinine and eGFR calculated using creatinine-based equations.

RESULTS

Of 53 patients, 30 (57%) were females and median age at diagnosis was 37.0 (range, 0.6-67.9) years. Median duration of follow-up was 10.3 (range, 0.0-31.5) years. At diagnosis, kidney stones had developed in 29 (55%) patients and 20 (38%) had CKD stages 3 to 5, including 11 (21%) patients with stage 5. At latest follow-up, 33 (62%) patients had experienced kidney stones; 18 (34%), AKI; and 22 (42%), CKD stages 3 to 5. Of 14 (26%) patients with stage 5 CKD, 12 had initiated renal replacement therapy. Kidney stones recurred in 18 of 33 (55%) patients. The median eGFR slope was -0.38 (range, -21.99 to 1.42) mL/min/1.73m(2) per year in patients receiving treatment with an xanthine dehydrogenase inhibitor and -5.74 (range, -75.8 to -0.10) mL/min/1.73m(2) per year in those not treated prior to the development of stage 5 CKD (P=0.001).

LIMITATIONS

Use of observational registry data.

CONCLUSIONS

Progressive CKD and AKI episodes are major features of APRT deficiency, whereas nephrolithiasis is the most common presentation. Advanced CKD without a history of kidney stones is more prevalent than previously reported. Our data suggest that timely therapy may retard CKD progression.

Endogenously elevated bilirubin modulates kidney function and protects from circulating oxidative stress in a rat model of adenine-induced kidney failure

Mildly elevated bilirubin is associated with a reduction in the presence and progression of chronic kidney disease and related mortality, which may be attributed to bilirubin's antioxidant properties. This study investigated whether endogenously elevated bilirubin would protect against adenine-induced kidney damage in male hyperbilirubinaemic Gunn rats and littermate controls. Animals were orally administered adenine or methylcellulose solvent (vehicle) daily for 10 days and were then monitored for 28 days. Serum and urine were assessed throughout the protocol for parameters of kidney function and antioxidant/oxidative stress status and kidneys were harvested for histological examination upon completion of the study. Adenine-treated animals experienced weight-loss, polyuria and polydipsia; however, these effects were significantly attenuated in adenine-treated Gunn rats. No difference in the presence of dihydroadenine crystals, lymphocytic infiltration and fibrosis were noted in Gunn rat kidneys versus controls. However, plasma protein carbonyl and F2-isoprostane concentrations were significantly decreased in Gunn rats versus controls, with no change in urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine or kidney tissue F2-isoprostane concentrations. These data indicated that endogenously elevated bilirubin specifically protects from systemic oxidative stress in the vascular compartment. These data may help to clarify the protective relationship between bilirubin, kidney function and cardiovascular mortality in clinical investigations.

Recurrence of crystalline nephropathy after kidney transplantation in APRT deficiency and primary hyperoxaluria

Purpose of review

To provide transplant physicians with a summary of the pathogenesis and diagnosis of adenine phosphoribosyl transferase (APRT) deficiency and primary hyperoxaluria and, focussed on kidney transplantation, and to discuss interventions aimed at preventing and treating the recurrence of crystalline nephropathy in renal transplant recipients.

Source of information

Pubmed literature search.

Setting

Primary hyperoxaluria and APRT deficiency are rare inborn errors of human metabolism. The hallmark of these diseases is the overproduction and urinary excretion of compounds (2,8 dihydroxyadenine in APRT deficiency, oxalate in primary hyperoxaluria) that form urinary crystals. Although recurrent urolithiasis represents the main clinical feature of these diseases, kidney injury can occur as a result of crystal precipitation within the tubules and interstitium, a condition referred to as crystalline nephropathy. Some patients develop end-stage renal disease (ESRD) and may become candidates for kidney transplantation. Since kidney transplantation does not correct the underlying metabolic defect, transplant recipients have a high risk of recurrence of crystalline nephropathy, which can lead to graft loss. In some instances, the disease remains undiagnosed until after the occurrence of ESRD or even after kidney transplantation.

Key messages

Patients with APRT deficiency or primary hyperoxaluria may develop ESRD as a result of crystalline nephropathy. In the absence of diagnosis and adequate management, the disease is likely to recur after kidney transplantation, which often leads to rapid loss of renal allograft function. Primary hyperoxaluria, but not APRT deficiency, becomes a systemic disease at low GFR with oxalate deposition leading to malfunction in non-renal organs (systemic oxalosis). We suggest that these diagnoses should be considered in patients with low glomerular filtration rate (GFR) and a history of kidney stones. In APRT deficiency, stones may be confused with uric acid stones, unless specialized techniques are used (infrared spectroscopy or X-ray crystallography for urinary crystals or stone analysis; Fourier transform infrared microscopy for crystals in kidney biopsy). Where these are unavailable, and for confirmation, the diagnosis can be made by measurement of enzyme activity in red blood cell lysates or by genetic testing. In patients with primary hyperoxaluria, levels of urinary and plasma oxalate; and the presence of nearly pure calcium oxalate monohydrate in stones, which often also have an unusually pale colour and unorganized structure, increase diagnostic suspicion. Molecular genetic testing is the criterion measure. Lifelong allopurinol therapy, with high fluid intake if appropriate, may stabilize kidney function in APRT deficiency; if ESRD has occurred or is near, results with kidney transplantation after initiation of allopurinol are excellent. In primary hyperoxaluria recognized before ESRD, pyridoxine treatment and high fluid intake may lead to a substantial decrease in urinary calcium oxalate supersaturation and prevent renal failure. In non-responsive patients or those recognized later in their disease, liver transplantation cures the underlying defect and should be considered when the GFR falls below 30 ml/min/1.73 m²; in those which or near ESRD, liver transplantation and intensive dialysis before kidney transplantation may be considered to reduce the total body oxalate burden before kidney transplantation.

Limitations

The availability of diagnostic tests varies between countries and centres. Data on long term outcomes after kidney transplantation are limited, especially for APRT deficiency patients.

Implications

Increasing transplant physicians knowledge of APRT deficiency and primary hyperoxaluria should enable them to implement adequate diagnostic and therapeutic interventions, thereby achieving good outcomes after kidney transplantation.

2,8-Dihydroxyadenine Nephropathy Identified as Cause of End-Stage Renal Disease After Renal Transplant

Adenine phosphoribosyltransferase deficiency is a rare autosomal recessive disorder of uric acid metabolism that leads to formation and excretion of 2,8-dihydroxyadenine into urine. The low solubility of 2,8-dihydroxyadenine results in precipitation and formation of urinary crystals and renal stones. Patients with this disorder usually have recurrent nephrolithiasis and can develop nephropathy secondary to crystal precipitation in the renal parenchyma. The disease is most often underdiagnosed and can recur in renal transplant, causing graft failure. Lack of specific clinical manifestations, chemical and radiologic features identical to those shown with uric acid stones, and lack of awareness among clinicians are among the causes for the underdiagnoses of this treatable disease. Allopurinol, a xanthine dehydrogenase inhibitor, is the mainstay of treatment, supported by high fluid intake and dietary modifications. The possibility of adenine phosphoribosyl transferase deficiency should be considered in all cases of urolithiasis in children, patients with recurrent urolithiasis, and patients with urolithiasis associated with renal failure of unknown cause, including patients with end-stage renal disease and renal transplant recipients. Here, we report a case of a 41-year-old female patient who had a late diagnosis of 2,8-dihydroxyadenine nephropathy-induced end-stage renal disease, made on the native nephrectomy that accompanied the renal transplant, and who had a timely intervention that prevented recurrence in the graft.

Primary disease recurrence—effects on paediatric renal transplantation outcomes

Primary disease recurrence after renal transplantation is mainly diagnosed by examination of biopsy samples, but can also be associated with clinical symptoms. In some patients, recurrence can lead to graft loss (7-8% of all graft losses). Primary disease recurrence is generally associated with a high risk of graft loss in patients with focal segmental glomerulosclerosis, membranous proliferative glomerulonephritis, primary hyperoxaluria or atypical haemolytic uraemic syndrome. By contrast, disease recurrence is associated with a limited risk of graft loss in patients with IgA nephropathy, renal involvement associated with Henoch-Schönlein purpura, antineutrophil cytoplasmic antibody-associated glomerulonephritis or lupus nephritis. The presence of systemic diseases that affect the kidneys, such as sickle cell anaemia and diabetes mellitus, also increases the risk of delayed graft loss. This Review provides an overview of the epidemiology, pathophysiology and management of primary disease recurrence in paediatric renal graft recipients, and describes the overall effect on graft survival of each of the primary diseases listed above. With appropriate management, few paediatric patients should be excluded from renal transplantation programmes because of an increased risk of recurrence.