Kidney injury associated with liver transplantation.

INTRODUCTION: Kidney injury associated with paediatric liver transplantation (LT) is common, but its evaluation is challenging. Our aim was to analyse the presence of perioperative acute kidney injury (AKI) and study the prevalence of chronic kidney disease (CKD) using different glomerular filtration rate (GFR) estimation formulas. METHODS: We conducted a cross-sectional study in a cohort of children aged less than 18 years with a history of LT followed up for 5.42 years. We estimated the GFR using the creatinine-based Schwartz bedside formula (2009), the cystatin C-based Caucasian Asian Pediatric and Adult cohort (CAPA) equation and the combined Full-Age Spectrum (FAS) formula as modified by Pottel. We analysed the agreement between them using the Bland-Altman method and the kappa statistic. We measured the albumin level in urine, the urine volume adjusted to 100 mL of GFR and blood pressure. We performed univariate and multivariate analyses of the risk factors associated with CKD. RESULTS: The sample included 52 patients with a median age of 9.21 years. Fifteen (28.8%) had AKI. Five (10%) had CKD and the only associated risk factor was acute liver failure at the time of LT (odds ratio, 8.57; P = 0.04). There was poor agreement between the different estimation formulas. One patient was classified as having CKD with the Schwartz formula compared to four patients with the CAPA and the Pottel combined FAS formulas. Up to 42% of children without CKD had some positive marker of kidney injury. CONCLUSIONS: The exclusive use of the 2009 Schwartz bedside formula to estimate GFR may lead to underdiagnosis of CKD in children post LT. Other markers of kidney injury are common, and their detection may help prevent the progression of CKD.

Two new missense mutations in the protein interaction ASH domain of OCRL1 identified in patients with Lowe syndrome.

The oculocerebrorenal syndrome of Lowe is a rare X-linked disease characterized by congenital cataracts, proximal renal tubulopathy, muscular hypotonia and mental impairment. This disease is caused by mutations in the OCRL gene encoding membrane bound inositol polyphosphate 5-phosphatase OCRL1. Here, we examined the OCRL gene of two Lowe syndrome patients and report two new missense mutations that affect the ASH domain involved in protein-protein interactions. Genomic DNA was extracted from peripheral blood of two non-related patients and their relatives. Exons and flanking intronic regions of OCRL were analyzed by direct sequencing. Several bioinformatics tools were used to assess the pathogenicity of the variants. The three-dimensional structure of wild-type and mutant ASH domains was modeled using the online server SWISS-MODEL. Clinical features suggesting the diagnosis of Lowe syndrome were observed in both patients. Genetic analysis revealed two novel missense variants, c.1907T>A (p.V636E) and c.1979A>C (p.H660P) in exon 18 of the OCRL gene confirming the clinical diagnosis in both cases. Variant c.1907T>A (p.V636E) was inherited from the patient's mother, while variant c.1979A>C (p.H660P) seems to have originated de novo. Analysis with bioinformatics tools indicated that both variants are pathogenic. Both amino acid changes affect the structure of the OCRL1 ASH domain. In conclusion, the identification of two novel missense mutations located in the OCRL1 ASH domain may shed more light on the functional importance of this domain. We suggest that p.V636E and p.H660P cause Lowe syndrome by disrupting the interaction of OCRL1 with other proteins or by impairing protein stability.

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.

Polycystic Kidney Disease with Hyperinsulinemic Hypoglycemia Caused by a Promoter Mutation in Phosphomannomutase 2.

Hyperinsulinemic hypoglycemia (HI) and congenital polycystic kidney disease (PKD) are rare, genetically heterogeneous disorders. The co-occurrence of these disorders (HIPKD) in 17 children from 11 unrelated families suggested an unrecognized genetic disorder. Whole-genome linkage analysis in five informative families identified a single significant locus on chromosome 16p13.2 (logarithm of odds score 6.5). Sequencing of the coding regions of all linked genes failed to identify biallelic mutations. Instead, we found in all patients a promoter mutation (c.-167G>T) in the phosphomannomutase 2 gene (PMM2), either homozygous or in trans with PMM2 coding mutations. PMM2 encodes a key enzyme in N-glycosylation. Abnormal glycosylation has been associated with PKD, and we found that deglycosylation in cultured pancreatic ß cells altered insulin secretion. Recessive coding mutations in PMM2 cause congenital disorder of glycosylation type 1a (CDG1A), a devastating multisystem disorder with prominent neurologic involvement. Yet our patients did not exhibit the typical clinical or diagnostic features of CDG1A. In vitro, the PMM2 promoter mutation associated with decreased transcriptional activity in patient kidney cells and impaired binding of the transcription factor ZNF143. In silico analysis suggested an important role of ZNF143 for the formation of a chromatin loop including PMM2 We propose that the PMM2 promoter mutation alters tissue-specific chromatin loop formation, with consequent organ-specific deficiency of PMM2 leading to the restricted phenotype of HIPKD. Our findings extend the spectrum of genetic causes for both HI and PKD and provide insights into gene regulation and PMM2 pleiotropy.

Novel truncating mutations in the ClC-5 chloride channel gene in patients with Dent's disease.

BACKGROUND: Dent's disease is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and eventual renal failure. The disease is caused by mutations in the X-linked chloride channel CLCN5 gene, which encodes a 746-amino-acid protein expressed in renal tubules. These mutations have been reported in unrelated families from the UK, USA, Japan and other countries. We were interested in identifying additional mutations in the CLCN5 coding region of Spanish patients with Dent's disease. METHODS: Five patients from three unrelated Spanish families were studied. Leukocyte genomic DNA from patients and their relatives was used with CLCN5-specific primers for polymerase chain reaction amplification of the coding region and exon-intron boundaries. Amplified products were analysed by single-strand conformational polymorphism analysis, DNA sequencing and restriction enzyme analysis. RESULTS: Low-molecular-weight proteinuria and hypercalciuria were detected in all the patients, nephrocalcinosis in two patients, and rickets or osteopenia in three patients. We identified three new CLCN5 mutations consisting of two nonsense mutations, Leu433Stop and Arg718Stop, and an insertional frameshift mutation, 65insT, which results in a stop at codon 98. These three mutations predict truncated ClC-5 proteins that, respectively, lack 314, 649 and 28 amino acids at the carboxy terminus, and are likely to result in loss of function. These mutations were shown to co-segregate with the disease in each of the three families. CONCLUSIONS: Our study is the first to characterize mutations in the CLCN5 gene in Spanish patients with Dent's disease and expands the spectrum of CLCN5 mutations associated with this disease.