GAPVD1 and ANKFY1 Mutations Implicate RAB5 Regulation in Nephrotic Syndrome.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) is a frequent cause of CKD. The discovery of monogenic causes of SRNS has revealed specific pathogenetic pathways, but these monogenic causes do not explain all cases of SRNS. METHODS: To identify novel monogenic causes of SRNS, we screened 665 patients by whole-exome sequencing. We then evaluated the in vitro functional significance of two genes and the mutations therein that we discovered through this sequencing and conducted complementary studies in podocyte-like Drosophila nephrocytes. RESULTS: We identified conserved, homozygous missense mutations of GAPVD1 in two families with early-onset NS and a homozygous missense mutation of ANKFY1 in two siblings with SRNS. GAPVD1 and ANKFY1 interact with the endosomal regulator RAB5. Coimmunoprecipitation assays indicated interaction between GAPVD1 and ANKFY1 proteins, which also colocalized when expressed in HEK293T cells. Silencing either protein diminished the podocyte migration rate. Compared with wild-type GAPVD1 and ANKFY1, the mutated proteins produced upon ectopic expression of GAPVD1 or ANKFY1 bearing the patient-derived mutations exhibited altered binding affinity for active RAB5 and reduced ability to rescue the knockout-induced defect in podocyte migration. Coimmunoprecipitation assays further demonstrated a physical interaction between nephrin and GAPVD1, and immunofluorescence revealed partial colocalization of these proteins in rat glomeruli. The patient-derived GAPVD1 mutations reduced nephrin-GAPVD1 binding affinity. In Drosophila, silencing Gapvd1 impaired endocytosis and caused mistrafficking of the nephrin ortholog. CONCLUSIONS: Mutations in GAPVD1 and probably in ANKFY1 are novel monogenic causes of NS. The discovery of these genes implicates RAB5 regulation in the pathogenesis of human NS.

Current Trends, Evaluation, and Management of Pediatric Nephrolithiasis.

The incidence of pediatric nephrolithiasis has been steadily increasing for the past several decades, with a concomitant concerning increase in health care costs and burden to children with this disease. Recent population-based studies have also demonstrated a change in the current trends of pediatric nephrolithiasis that is characterized by a significant increase in the number of girls now being affected. While changes in diet and lifestyle, obesity prevalence, and even imaging practices have been proposed to contribute to the recent increase in pediatric nephrolithiasis, a definite underlying cause remains elusive. This situation is complicated by the fact that, unlike in adults, the trends occurring in pediatric nephrolithiasis have not been studied rigorously, which contributes to the paucity of data in children. The level of concern with the increasing incidence is raised by factors unique to pediatric nephrolithiasis that could expose an affected child to more complications. Factors such as variable clinical presentation, high recurrence of kidney stones associated with abnormalities of metabolism and the urinary tract, and the possible presence of rare genetic kidney stone diseases would require physicians to comprehensively evaluate patients presenting with kidney stones. The goal of evaluation is to identify modifiable risk factors and abnormalities for which targeted therapy can be prescribed. The goals of medical and surgical treatments are to eliminate the burden of kidney stones and prevent recurrence while simultaneously minimizing complications from interventions. Patients at high risk may benefit from a specialized kidney stone clinic staffed by a pediatric nephrologist, urologist, dietitian, and clinical nurse. Such a multidisciplinary clinic can help provide the medical and surgical support needed for patients at high risk and offer key opportunities to learn more about pediatric nephrolithiasis, thereby fueling the much-needed research in this field.

Design of the Nephrotic Syndrome Study Network (NEPTUNE) to evaluate primary glomerular nephropathy by a multidisciplinary approach.

The Nephrotic Syndrome Study Network (NEPTUNE) is a North American multicenter collaborative consortium established to develop a translational research infrastructure for nephrotic syndrome. This includes a longitudinal observational cohort study, a pilot and ancillary study program, a training program, and a patient contact registry. NEPTUNE will enroll 450 adults and children with minimal change disease, focal segmental glomerulosclerosis, and membranous nephropathy for detailed clinical, histopathological, and molecular phenotyping at the time of clinically indicated renal biopsy. Initial visits will include an extensive clinical history, physical examination, collection of urine, blood and renal tissue samples, and assessments of quality of life and patient-reported outcomes. Follow-up history, physical measures, urine and blood samples, and questionnaires will be obtained every 4 months in the first year and biannually, thereafter. Molecular profiles and gene expression data will be linked to phenotypic, genetic, and digitalized histological data for comprehensive analyses using systems biology approaches. Analytical strategies were designed to transform descriptive information to mechanistic disease classification for nephrotic syndrome and to identify clinical, histological, and genomic disease predictors. Thus, understanding the complexity of the disease pathogenesis will guide further investigation for targeted therapeutic strategies.

Technical approach to iliac crest biopsy.

Bone histomorphometry has been the gold standard in the evaluation and diagnosis of renal osteodystrophy. The recent new definition of renal osteodystrophy as chronic kidney disease-mineral and bone disorder has once again highlighted the use of bone biopsy as a powerful and diagnostic tool to determine skeletal abnormalities in chronic kidney disease. The procedure of iliac crest bone biopsy has been proved safe and associated with very minimal morbidity. In this review, the clinical indications, preparation, instrumentation, and potential complications are discussed. Because current biochemical markers are poor predictors of bone turnover, volume, and mineralization, a wider use of bone biopsy and histomorphometry will lead to a better understanding of the bone and mineral disorders that are associated with chronic kidney disease.

Osteomalacia in a hemodialysis patient receiving an active vitamin D sterol.

BACKGROUND: A 17-year-old Filipino male hemodialysis patient presented for renal transplant evaluation. He had significant skeletal abnormalities characterized by bone pain, an inability to walk, and secondary hyperparathyroidism despite therapy with an active vitamin D sterol (paricalcitol). INVESTIGATIONS: The patient underwent a physical examination, and his serum levels of calcium, phosphorus, alkaline phosphatase, parathyroid hormone, aluminum and 25-hydroxycholecalciferol (25OH-vitamin D) were determined. X-rays of hips and lower extremities, MRI, and bone histomorphometry after double tetracycline labeling were performed. DIAGNOSIS: Osteomalacia associated with low 25OH-vitamin D levels. MANAGEMENT: Monthly therapy with ergocalciferol (vitamin D2) and discontinuation of paricalcitol.

Fatty acid ethyl esters in meconium: are they biomarkers of fetal alcohol exposure and effect?

BACKGROUND: Biomarkers of fetal exposure to alcohol are important to establish so that early detection and intervention can be made on these infants to prevent undesirable outcomes. The aim of this study was to analyze long-chain fatty acid ethyl esters (FAEEs) in meconium as potential biomarkers of fetal alcohol exposure and effect. METHODS: Fatty acid ethyl esters were analyzed in the meconium of 124 singleton infants by positive chemical ionization gas chromatography/mass spectrometry (GC/MS) and correlated to maternal ethanol use. RESULTS: A total of 124 mother/infant dyads were enrolled in the study: 31 were in the control group and 93 were in the alcohol-exposed group. The incidence (28% vs 9.7%, p = 0.037) of ethyl linoleate detected in meconium was significantly higher in the alcohol-exposed groups than the control groups. Similarly, when the concentrations of ethyl linoleate in meconium were grouped (trichotomized), there was a significant linear by linear association between alcohol exposure and group concentrations of ethyl linoleate (p = 0.013). Furthermore, only alcohol-exposed infants were found in the group with the highest ethyl linoleate concentration. The sensitivity of ethyl linoleate in detecting prenatal alcohol exposure was only 26.9%, and its specificity and positive predictive value were 96.8 and 96.2%, respectively. There was no significant correlation between the concentration of ethyl linoleate in meconium and absolute alcohol consumed (oz) per drinking day across pregnancy, although a trend toward a positive correlation is seen at lower amounts of alcohol consumed. Among the polyunsaturated, long-chain FAEEs, there was weak evidence that the incidence (21.5% vs 6.5%, p = 0.057) and concentration (p = 0.064) of ethyl arachidonate (AA) were significantly higher in the alcohol-exposed groups than the control groups. Ethyl linolenate and ethyl docosahexanoate (DHA) in meconium were found only in the alcohol group, although not at statistically significant levels. Highly significant correlations were found among the concentrations of ethyl linoleate, ethyl linolenate, ethyl AA, and ethyl DHA in meconium (correlations ranged between rs = 0.203, p = 0.024; and rs = 0.594, p < 0.001). CONCLUSION: We conclude that FAEEs in meconium, particularly ethyl linoleate and ethyl AA, are biomarkers of high specificity for prenatal exposure to alcohol in newborn infants. We also propose that ethyl AA and DHA could be potential biomarkers of fetal alcohol effects on the developing fetal brain and should be investigated further.

Role of parathyroid hormone and therapy with active vitamin D sterols in renal osteodystrophy.

Renal osteodystrophy (ROD) represents a spectrum of bone lesions ranging from a high-turnover to a low-turnover state. The expression of the histologic bone lesions is modulated by parathyroid hormone (PTH), vitamin D, calcium, phosphorus, and aluminum that act as major regulators of osteoblastic activity and bone formation rate. The availability of immunometric PTH assays has allowed reasonable prediction of the subtypes of bone lesions in patients with chronic kidney disease (CKD). PTH levels as measured by these assays, however, may not reflect the true bone turnover state during treatment with intermittent active vitamin D. Early diagnosis and appropriate treatment of renal bone disease are essential in preventing the debilitating consequences of ROD on the growing skeleton. Calcitriol and calcium-containing phosphate binders have been the mainstay of treatment for secondary hyperparathyroidism. Complications such as hypercalcemia, vascular calcifications, and the development of adynamic bone may arise from aggressive treatment. New vitamin D analogs and calcium-free phosphate binders are promising in terms of limiting these complications. The management of ROD should be tailored to maintain normal rates of bone formation and turnover with age-appropriate serum calcium and phosphorus levels and with serum PTH levels that correspond to normal rates of skeletal remodeling. These treatment goals would maintain bone health, maximize growth potential, and prevent the development of soft tissue and vascular calcifications.