Use of rasburicase to improve kidney function in children with hyperuricemia and acute kidney injury.

BACKGROUND: Hyperuricemia contributes to decrease in kidney function and induces additional renal damage in children with acute kidney injury (AKI). Rasburicase oxidizes uric acid (UA), decreasing its serum quantities in less than 24 h. METHODS: This is a retrospective study involving hospitalized patients under 18 years of age with underlying pathology diagnosed with AKI and severe hyperuricemia treated with rasburicase over a 4-year period. RESULTS: We describe 15 patients from 4 days of life to 18 years (median: 4.4 years). Seventy-three percent had known underlying pathologies. All presented worsening of basal renal function or AKI data. All received the usual medical treatment for AKI without response. Twenty percent received an extrarenal depuration technique. All had hyperuricemia with a mean (± SD) of 13.1 (± 2.19) mg/dl. After rasburicase administration UA levels fell to a mean (± SD) of 0.76 (± 0.62) mg/dl (p < 0.001) in less than 24 h. In parallel, a decrease in the mean plasma creatinine was observed (2.92 mg/dl to 1.93 mg/dl (p = 0.057)) together with a significant improvement of the mean glomerular filtration rate (16.3 ml/min/1.73 m2 to 78.6 ml/min/1.73 m2) (p = 0.001)). No side effects were recorded. Kidney function normalized in all cases or returned to baseline levels. CONCLUSIONS: Although the use of rasburicase is not routinely approved in pediatric patients with severe hyperuricemia and AKI, it has been used successfully without complications, and helped prevent progressive kidney damage. This study could serve as a basis for suggesting the off-label use of rasburicase for the management of complex pediatric patients in whom UA plays an important role in the development of AKI.

Secondary Immunosuppression in Pediatric Kidney Transplant Recipients.

OBJECTIVES: Currentimmunosuppressive treatments for kidney transplant recipients have improved graft viability at the expense of impaired immune surveillance. The tools for monitoring immune status in pediatric kidney transplant recipients have not been widely investigated. Better knowledge could help recognize over immunosuppression and allow implementation of individualized preventive strategies. MATERIALS AND METHODS: This retrospective and observational study included 28 pediatric kidney transplant recipients treated at a tertiary hospital. We measured peripheral blood lymphocyte subpopulations, immunoglobulins, immunosuppressivedrug levels, and viral loads. Reference analytical values for different age ranges were used to determine immune status. We recorded overall hospitalizations due to opportunistic infections and positive viral loads posttransplant. RESULTS: We found hypogammaglobulinemia and lymphopenia in 19% and 41% of the patients, respectively. Peripheral blood lymphocyte subpopulations were below normal limits in one-third of the sample. These parameters were not related to the current number or plasma levels of immunosuppressive drugs. During follow-up, cytomegalovirus, Epstein-Barr virus, and BK virus viremias were detected in 60.7% of the patients. Admissions due to opportunistic infections happened in 57.1%, mainly related to severe viral disease (30%) or gastrointestinal infections (26.7%). Most occurred in younger transplant recipients and during the first 2 years posttransplant (73.3%). We found no significant relation between peripheral blood lymphocyte subpopulations and hospital admissions for opportunistic infections or positive viral loads during follow-up. CONCLUSIONS: Recurrent hospitalizations for opportunistic infections and analytical disorders in the immune system suggested that secondary immunosuppression in pediatric kidney transplant recipients was frequent. Immunosuppression was not directly related to plasma drug levels or the number of immunosuppressive drugs. Thus, immune monitoring might be helpful in combination with immunosuppressant levels to assess immunosuppression status and to establish individualized preventive measures.

Clinical and genetic characterization of a cohort of proteinuric patients with biallelic CUBN variants.

BACKGROUND: Proteinuria is a well-known risk factor for progressive kidney impairment. Recently, C-terminal cubilin (CUBN) variants have been associated with isolated proteinuria without progression of kidney disease. METHODS: Genetic testing of 347 families with proteinuria of suspected monogenic cause was performed by next-generation sequencing of a custom-designed kidney disease gene panel. Families with CUBN biallelic proteinuria-causing variants were studied at the clinical, genetic, laboratory and pathologic levels. RESULTS: Twelve families (15 patients) bearing homozygous or compound heterozygous proteinuria-causing variants in the C-terminal CUBN gene were identified, representing 3.5% of the total cohort. We identified 14 different sequence variants, five of which were novel. The median age at diagnosis of proteinuria was 4 years (range 9 months to 44 years), and in most cases proteinuria was detected incidentally. Thirteen patients had moderate to severe proteinuria at diagnosis without nephrotic syndrome. These patients showed lack of response to angiotensin-converting enzyme inhibitor (ACEi) and angiotensin receptor blocker (ARB) treatment, normal kidney biopsy and preservation of normal kidney function over time. The two remaining patients presented a more severe phenotype, likely caused by associated comorbidities. CONCLUSIONS: Identification of C-terminal pathogenic CUBN variants is diagnostic of an entity characterized by glomerular proteinuria, normal kidney histology and lack of response to ACEi/ARB treatment. This study adds evidence and increases awareness about albuminuria caused by C-terminal variants in the CUBN gene, which is a benign condition usually diagnosed in childhood with preserved renal function until adulthood.

Novel variant in the CNNM2 gene associated with dominant hypomagnesemia.

The maintenance of magnesium (Mg2+) homeostasis is essential for human life. The Cystathionine-ß-synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) have been described to be involved in maintaining Mg2+ homeostasis. Among these CNNMs, CNNM2 is expressed in the basolateral membrane of the kidney tubules where it is involved in Mg2+ reabsorption. A total of four patients, two of them with a suspected disorder of calcium metabolism, and two patients with a clinical diagnosis of primary tubulopathy were screened for mutations by Next-Generation Sequencing (NGS). We found one novel likely pathogenic variant in the heterozygous state (c.2384C>A; p.(Ser795*)) in the CNNM2 gene in a family with a suspected disorder of calcium metabolism. In this family, hypomagnesemia was indirectly discovered. Moreover, we observed three novel variants of uncertain significance in heterozygous state in the other three patients (c.557G>C; p.(Ser186Thr), c.778A>T; p.(Ile260Phe), and c.1003G>A; p.(Asp335Asn)). Our study shows the utility of Next-Generation Sequencing in unravelling the genetic origin of rare diseases. In clinical practice, serum Mg2+ should be determined in calcium and PTH-related disorders.

Hypophosphataemic Rickets: Similar Phenotype of Different Diseases.

Hypophosphataemic rickets (HR) is a group of rare disorders caused by excessive renal phosphate wasting in which the participation of fibroblast growth factor 23 (FGF23) can be prominent. These diseases pose therapeutic challenges with important consequences for growth and bone development in childhood, with higher risk of fractures and poorer bone healing, dental problems, and nephrolithiasis or nephrocalcinosis. In some cases, the diagnostic delay can be very long; laboratory findings and an exhaustive anamnesis could help distinguish between various pathologies, and FGF23 values-although currently not routinely measured-have implications for the differential diagnosis. Genetic testing is encouraged, especially in sporadic or insidious cases. In this review we discuss the clinical features of HR, with a particular emphasis on the differential diagnosis and the therapeutic implications.

Variable phenotype in HNF1B mutations: extrarenal manifestations distinguish affected individuals from the population with congenital anomalies of the kidney and urinary tract.

BACKGROUND: Mutations in hepatocyte nuclear factor 1B (HNF1B) have been associated with congenital anomalies of the kidney and urinary tract (CAKUT) in humans. Diabetes and other less frequent anomalies have also been described. Variable penetrance and intrafamilial variability have been demonstrated including severe prenatal phenotypes. Thus, it is important to differentiate this entity from others with similar clinical features and perform confirmatory molecular diagnosis. METHODS: This study reports the results of HNF1B screening in a cohort of 60 patients from 58 unrelated families presenting with renal structural anomalies and/or non-immune glucose metabolism alterations, and other minor features suggesting HNF1B mutations. RESULTS: This study identified a pathogenic variant in 23 patients from 21 families. The most frequent finding was bilateral cystic dysplasia or hyperechogenic kidneys (87% of patients). Sixty percent of them also fulfilled the criteria for impaired glucose metabolism, and these were significantly older than those patients with an HNF1B mutation but without diabetes or prediabetes (14.4 versus 3.3 years, P < 0.05). Furthermore, patients with HNF1B mutations had higher frequency of pancreatic structural anomalies and hypomagnesaemia than patients without mutations (P < 0.001 and P = 0.003, respectively). Hyperuricaemia and increased liver enzymes were detected in some patients as well. CONCLUSIONS: Renal anomalies found in patients with HNF1B mutations are frequently unspecific and may resemble those found in other renal pathologies (CAKUT, ciliopathies). Active searching for extrarenal minor features, especially pancreatic structural anomalies or hypomagnesaemia, could support the indication for molecular diagnosis to identify HNF1B mutations.