Choni Rinat

Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23.

Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C‐terminal fragments. FGF23 protein has three O‐linked glycans and FGF23 with incomplete glycosylation is susceptible to processing. Silencing GALNT3 resulted in enhanced processing of FGF23. Decreased function of FGF23 by enhanced processing is the cause of hyperphosphatemia in patients with GALNT3 mutation.

Dent’s disease manifesting as focal glomerulosclerosis: Is it the tip of the iceberg?

Dent’s disease is an X-linked proximal tubulopathy. It often manifests in childhood with symptoms of Fanconi syndrome and low-molecular-weight proteinuria. We describe four boys from three unrelated families whose only presenting symptoms of Dent’s disease were nephrotic-range proteinuria and histological findings of focal segmental and/or global glomerulosclerosis. In all families, a causal mutation in the CLCN5 gene, encoding a voltage-gated chloride transporter and chloride-proton exchanger, was identified. All three mutations are pathogenic: two are novel (p.Asp727fs and p.Trp122X), and one is a recurrent mutation, p.R648X. Given the atypical phenotype of these patients with Dent’s disease, it is possible that this clinical entity is markedly underdiagnosed and that our report represents only the tip of the iceberg. The diagnosis of Dent’s disease should be considered in all patients with nephrotic-range proteinuria without hypoalbuminemia or edema. Establishing the diagnosis of Dent’s disease will prevent the administration of unnecessary immunosuppressive medications with their undesirable side effects.

Risk Factors for Cardiovascular Disease in Children and Young Adults after Renal Transplantation

Despite good outcomes in pediatric renal transplantation, life expectancy is reduced, mostly as a result of accelerated atherosclerosis. A comprehensive evaluation of cardiac status and risk factors for cardiovascular disease was performed in 60 patients after renal transplantation (age 3 to 29 yr; mean 15.8). Posttransplantation diabetes was diagnosed in 7%. Half of the patients did not engage in any physical activity, and this was associated with increased body mass index. Uncontrolled hypertension was found in 13% of patient, and 53% were on antihypertensive medications. BP index was associated with left ventricular mass index (LVMI). Dyslipidemia was relatively uncommon, with hypercholesterolemia found in 15% and elevated LDL cholesterol found in 10% of patients. Hyperhomocysteinemia was frequent (58%); in most patients, it was not due to folate or B(12) deficiency. Lipid and homocysteine abnormalities were associated with cyclosporine therapy. Echocardiography demonstrated normal LVMI in 93% of patients, although LVMI was higher than in healthy control subjects. Cardiac troponin I was normal in all patients, but N-terminal pro-brain natriuretic peptide was elevated in 35% and was associated with LVMI and renal function. Although present cardiac status is relatively normal in pediatric renal transplantation patients, cardiac risk factors are common, and strategies to prevent cardiovascular disease need to be developed.

Recurrent Nephrotic Syndrome in Homozygous Truncating NPHS2 Mutation Is Not Due to Anti‐Podocin Antibodies

Mutations in NPHS2 are a common cause of focal segmental glomerulosclerosis (FSGS). It was initially assumed that FSGS caused by a genetically defective protein in the native kidney would not recur after transplantation; however, description of three patients with NPHS2 missense mutations challenged the validity of this assumption. A possible mechanism of recurrence in cases with stop‐codon mutations is the formation of auto‐antibodies against the truncated protein. In this case report, we describe a 9‐year‐old girl with the R138X NPHS2 mutation who presented with recurrent nephrotic syndrome 4 years after renal transplantation from a deceased donor, and was treated with plasmapheresis with a partial response. Renal histology did not demonstrate glomerular immunoglobulin deposition and an extensive search for anti‐podocin antibodies based on indirect Western blot with recombinant podocin, was negative, as was the test for glomerular permeability factor (Palb). Taken together these findings confirm the possibility of post transplantation nephrotic syndrome in patients with NPHS2 mutations. Lack of immunoglobulin deposition, absence of circulating anti‐podocin antibodies, and normal Palb suggest that other, unknown pathogenetic mechanisms are implicated.

Genetic analysis – a diagnostic tool for primary hyperoxaluria type I

We read with great interest the article “Genetic analysis: a diagnostic tool for primary hyperoxaluria type 1 (PH1)”, published online in Pediatric Nephrology on 9 October 2002 by Danko Milosevic and colleagues, but disagree with some of the conclusions. The authors correctly point out that the diagnosis “is confirmed by the measurement of decreased alanine:glyoxylate aminotransferase activity in a liver sample”. They further state that this “enzymatic assay is not readily available to pediatric nephrologists in many parts of the world”, since “shipment of a frozen liver sample abroad is cumbersome and expensive” and propose, as an alternative, mutation analysis by sequencing of the entire coding region of the AGXT gene. We feel strongly that this approach deserves further comment. Clinical diagnosis of PH1 and its distinction from type 2 and other, as yet unclassified, forms of primary hyperoxaluria [1, 2] is difficult and, despite extensive clinical and laboratory work-up of urine metabolites (glycollate/L-glycerate) can, in some cases, be inconclusive without liver biopsy [3]. Milosevic et al. correctly recommend combined liver and kidney transplantation as treatment of the severe forms of PH1. With such a major step, all transplant centers throughout the world should demand a definite diagnosis of PH1 (or PH2) and offer the means to ship a frozen liver sample to a specialized laboratory. Genetic analysis in PH1 is a diagnostic tool that we also frequently use for family studies when definite diagnosis of an index patient has been performed by liver enzyme assay. In these cases either mutation analysis of the more frequent mutations, such as G630A, C156ins, or T853C, or linkage analysis using microsatellites is feasible [4, 5, 6]. However, screening for these common mutations has a sensitivity of less than 50% [4] and, in the majority of patients, will not lead to a definite diagnosis of PH1 due to the great number of mutations described. Exceptions to this may occur in populations with a high prevalence of single mutations, when screening for this particular mutation may lead to a high diagnostic sensitivity and specificity. Direct cycle sequencing of the entire coding region, as recommended by Milosevic et al., is by no means readily available to pediatric nephrologists in many parts of the world, and is mainly performed in centers with a scientific interest in this disease who may therefore not charge for this expensive laboratory method. It has the additional disadvantage that even this approach does not have 100% sensitivity, as illustrated by the finding of only a single mutation in family S described by Milosevic and colleagues. This suggests that mutations in the promoter region or intronic regions of the gene may be overlooked. Finally, in such a polymorphic gene, the Authors’ reply to this letter is available at http://dx.doi.org/ 10.1007/s00467-003-1108-2

The Heart of Children with Steroid-Resistant Nephrotic Syndrome: Is It All Podocin?

Mutations in the gene NPHS2 encoding podocin are responsible for a recessive form of steroid-resistant nephrotic syndrome (SRNS). The common phenotype is of massive proteinuria in early childhood that tends to progress to end-stage renal failure. Extrarenal manifestations have not been described. Twenty-two children with SRNS from six unrelated Arab families were found to be homozygous for the R138X mutation in NPHS2. Eighteen patients underwent cardiac evaluation at diagnosis of SRNS while they had normal BP and preserved renal function. Cardiac anomalies were detected in 16 (89%) children: Left ventricular hypertrophy in eight, pulmonary stenosis in six, discrete subaortic stenosis in two, and Ebstein anomaly and ventricular septal defect in one each. The remaining four affected individuals were assessed only once they had end-stage renal failure. They had severe left ventricular hypertrophy and experienced repeated episodes of heart failure. Two control groups were equally evaluated. The first consisted of 37 siblings without nephrotic syndrome, of whom only one carrier had a cardiac defect (P < 0.001). None of the second group, which included 22 children with persistent nephrotic syndrome as a result of other causes, had a cardiac anomaly (P < 0.001). Cardiac disorders in homozygotes for mutations in NPHS2 cannot be attributed to an association by chance or to a state of persistent nephrotic syndrome. Because human podocin mRNA is expressed in fetal heart, it is speculated that it may have a role in normal cardiac development. Cardiac evaluation is recommended at the time of diagnosis of SRNS due to mutations in podocin.

Intra-Familial Clinical Heterogeneity: Absence of Genotype-Phenotype Correlation in Primary Hyperoxaluria Type 1 in Israel

Background/Aims: Primary hyperoxaluria type 1 (PH1) is caused by the deficiency of the liver enzyme alanine:glyoxylate aminotransferase which results in increased synthesis and excretion of oxalate. The clinical manifestations of PH1 are heterogeneous with respect to the age of onset and rate of progression. The aim of this study was to investigate possible relationships between a given genotype, the biochemical profile and the clinical phenotype. Methods: We conducted a study of 56 patients from 22 families with PH1 from Israel. The clinical and biochemical data were compiled and the genotype was determined for each family. Results: The prevalent phenotype was of early onset with progression to end-stage renal disease during the first decade of life. Fifteen PH1-causing mutations were detected in 21 families: 10 were first described in this patient population. Marked intra-familial clinical heterogeneity was noted, meaning that there was no correlation between a given genotype and the phenotype. Conclusions: The clinical course of patients with PH1 is not dictated primarily by its genotype. Other genetic and/or environmental factors play a role in determining the ultimate phenotype.

Familial inheritance of crossed fused renal ectopia.

Abstract A family with dominant inheritance of a rare renal malformation is reported. The father and one son had left crossed fused ectopic and dysplastic kidneys and another son had a horseshoe kidney and vesicoureteral reflux. We discuss various potential pathogenetic mechanisms and propose that a defect in the timing of the proper reciprocal induction of the ureteric bud and the metanephric blastema is involved.

Misleading findings of homozygosity mapping resulting from three novel mutations in NPHS1 encoding nephrin in a highly inbred community

Purpose: Congenital nephrotic syndrome of the Finnish type (CNF, NPHS1) is a rare autosomal recessive disease caused by mutations in the NPHS1 gene encoding nephrin. We diagnosed congenital nephrotic syndrome in 12 children living in a village near Jerusalem. Most of the inhabitants are descendants of one Muslim family and have maintained their isolation by preference of consanguineous marriages. The aim of this study was to confirm that the NPHS1 gene is responsible for congenital nephrotic syndrome in our population, applying homozygosity mapping.Methods: DNA samples were genotyped by four microsatellite markers that were in linkage disequilibrium with the NPHS1 gene on chromosome 19q13.1. Immunoperoxidase staining was used to study the expression of nephrin, and mutations were subsequently identified by direct sequencing of the entire coding region of the NPHS1 gene.Results: Haplotype analysis revealed several different haplotypes, leading us to assume erroneously that there was genetic heterogeneity of congenital nephrotic syndrome. Because nephrin was completely absent in kidney tissue of one patient, direct sequencing of all DNA samples was performed, yielding three novel mutations: c.1138C>T (p.Gln380X), c.2160_ 2161insC (p.Cys721fs), and c.1707C>G (p.Ser569Arg). Patients were either homozygous for one of these mutations or compound heterozygotes, and they differed in their phenotype.Conclusion: We report the potential pitfalls of performing homozygosity mapping in a highly consanguineous population and discuss the phenomenon of multiple mutations in a given gene within an isolate.

Hypothyroidism in primary hyperoxaluria type 1

We describe 4 patients, aged 3 months to 23 years, with end-stage renal disease and severe, symptomatic hypothyroidism. All 4 had primary hyperoxaluria type 1 (PH1) with diffuse tissue (kidneys, skeleton, eyes, heart) calcium-oxalate deposition, a condition known as oxalosis. The hypothyroidism responded to thyroid hormone replacement therapy. Clinical hypothyroidism within the framework of PH1/oxalosis was probably caused by thyroid tissue damage from an abundance of calcium oxalate. We recommend that thyroid function be monitored in patients with PH1 and oxalosis.