Loss of function of NaPiIIa causes nephrocalcinosis and possibly kidney insufficiency.

BACKGROUND: Inherited metabolic disorders associated with nephrocalcinosis are rare conditions. The aim of this study was to identify the genetic cause of an Israeli-Arab boy from a consanguineous family with severe nephrocalcinosis and kidney insufficiency. METHODS: Clinical and biochemical data of the proband and family members were obtained from both previous and recent medical charts. Genomic DNA was isolated from peripheral blood cells. The coding sequence and splice sites of candidate genes (CYP24A1, CYP27B1, FGF23, KLOTHO, SLC34A3 and SLC34A1) were sequenced directly. Functional studies were performed in Xenopus laevis oocytes and in transfected opossum kidney (OK) cells. RESULTS: Our patient was identified as having nephrocalcinosis in utero, and at the age of 16.5 years, he had kidney insufficiency but no bone disease. Genetic analysis revealed a novel homozygous missense mutation, Arg215Gln, in SLC34A1, which encodes the renal sodium phosphate cotransporter NaPiIIa. Functional studies of the Arg215Gln mutant revealed reduced transport activity in Xenopus laevis oocytes and increased intracellular cytoplasmic accumulation in OK cells. CONCLUSIONS: Our findings show that dysfunction of the human NaPiIIa causes severe renal calcification that may eventually lead to reduced kidney function, rather than complications of phosphate loss.

Maternal and infantile hypercalcemia caused by vitamin-D-hydroxylase mutations and vitamin D intake.

BACKGROUND: Hypercalcemia is caused by many different conditions and may lead to severe complications. Loss-of-function mutations of CYP24A1, encoding vitamin D-24-hydroxylase, have recently been identified in idiopathic infantile hypercalcemia and in adult kidney stone disease. The aim of this study was to investigate the genetics and clinical features of both infantile and maternal hypercalcemia. METHODS: We studied members of four unrelated Israeli families with hypercalcemia, namely, one woman during pregnancy and after delivery and three infants. Clinical and biochemical data were obtained from probands' medical charts. Genomic DNA was isolated from peripheral blood and CYP24A1 was sequenced. RESULTS: Typical symptoms of hypercalcemia associated with the intake of recommended doses of vitamin D developed in the infants and pregnant woman. Four different loss-of-function CYP24A1 mutations were identified, two of which are reported here for the first time (p.Trp134Gly and p.Glu315*). The infants from families 1 and 2, respectively, were found to be compound heterozygotes, and the infant from family 3 and the pregnant woman were found to be homozygous. CONCLUSIONS: This is the first report of maternal hypercalcemia caused by a CYP24A1 mutation, showing that not only infants are at risk for this complication. Our findings emphasize the importance of recognition, genetic diagnosis and proper treatment of this recently identified hypercalcemic disorder in this era of widespread vitamin D supplements.

Chronic hypercalcaemia from inactivating mutations of vitamin D 24-hydroxylase (CYP24A1): implications for mineral metabolism changes in chronic renal failure.

BACKGROUND: Loss-of-function mutations of vitamin D-24 hydroxylase have recently been recognized as a cause of hypercalcaemia and nephrocalcinosis/nephrolithiasis in infants and adults. True prevalence and natural history of this condition are still to be defined. METHODS: We describe two adult patients with homozygous mutations and six related heterozygous carriers. Mineral and hormonal data in these patients were compared with that in 27 patients with stage 2-3 chronic kidney disease and 39 healthy adult kidney donors. RESULTS: Probands had recurrent nephrolithiasis, chronic hypercalcaemia with depressed parathyroid hormone (PTH) and increased 1,25(OH)(2)D levels; carriers had nephrolithiasis (two of six), hypercalciuria (two of six) and high or normal-high 1,25(OH)(2)D (four of four). Corticosteroids did not reduce plasma and urine calcium levels, but ketoconazole did, indicating that 1,25(OH)(2)D production is not maximally depressed despite coexisting hypercalcaemia, high 1,25(OH)(2)D and depressed PTH, and that 1,25(OH)(2)D degradation through vitamin D-24 hydroxylase is a regulator of plasma 1,25(OH)(2)D levels. Both probands had vascular calcifications and high bone mineral content. One developed stage 3b renal failure: in this patient 1,25(OH)(2)D decreased within normal limits as glomerular filtration rate (GFR) fell and PTH rose to high-normal values, yet hypercalcaemia persisted and the ratio of 1,25(OH)(2)D to GFR remained higher than normal for any degree of GFR. CONCLUSIONS: This natural model indicates that vitamin D-24 hydroxylase is a key physiologic regulator of calcitriol and plasma calcium levels, and that balanced reduction of 1,25(OH)(2)D and GFR is instrumental for the maintenance of physiologic calcium levels and balance in chronic kidney diseases.

Loss-of-function mutations of CYP24A1, the vitamin D 24-hydroxylase gene, cause long-standing hypercalciuric nephrolithiasis and nephrocalcinosis.

PURPOSE: Hypercalciuria is the most common cause of kidney stone disease and genetic factors have an important role in nearly half of these cases. Recently loss-of-function mutations of CYP24A1, the gene encoding vitamin D 24-hydroxylase, were identified in idiopathic infantile hypercalcemia. We describe the clinical and molecular basis of severe long-standing kidney stone disease in adults caused by CYP24A1 mutations. MATERIALS AND METHODS: Three subjects from 2 Israeli families with nephrolithiasis and nephrocalcinosis were clinically characterized. Genomic DNA was isolated from peripheral blood and sequencing of CYP24A1 was performed. RESULTS: All subjects presented with severe kidney stone disease, the cause of which was not discovered for decades despite extensive evaluation. They all had hypercalciuria, nephrocalcinosis and intermittent hypercalcemia, and chronic kidney insufficiency developed in the oldest subject. All patients had a typical pattern of test results, including normal-high serum calcium, low parathyroid hormone levels, high vitamin D 25-(OH)D3 and 1,25-(OH)2D3, and low 24,25-(OH)2D3. Overall 3 CYP24A1 loss-of-function mutations were identified, including a homozygous deletion (delE143) in consanguinous family 1, and compound heterozygous mutations L409S and the novel W268-stop in family 2. CONCLUSIONS: Loss-of-function mutations of CYP24A1 gene, encoding for 1,25-dihydroxyvitamin D3 24-hydroxylase, cause severe hypercalciuric nephrolithiasis and nephrocalcinosis. The mutations may present in adults and may lead to chronic renal insufficiency. Our results support a recessive mode of inheritance. CYP24A1 mutations should be considered in the differential diagnosis of hypercalciuric nephrolithiasis, especially as many adults are now prescribed supplemental oral vitamin D.

Peritoneal dialysis in patients with refractory congestive heart failure: potential prognostic factors.

BACKGROUND: Peritoneal dialysis (PD) is increasingly used for long-term management of refractory congestive heart failure (CHF). In this study, we investigated the outcome of patients with refractory CHF treated with PD, aiming to identify potential prognostic factors for long term-survival. METHODS: This was a prospective observational study over a period of 42 months which included 37 refractory CHF patients. RESULTS: Median survival on PD was 14 months (1-41 months). Long survivors had serum sodium >132 mEq/l (p < 0.001), serum albumin >3.2 g/dl (p < 0.001) and hospitalization rate <2 days per month a year before starting the treatment (p = 0.008). Patients in the lowest survival quartile had lower serum albumin (2.8 vs. 3.5 g/dl in longer survivors, p = 0.003) and serum sodium (126 vs. 137 mEq/l, p < 0.0001), higher serum leukocyte count (7,500 vs. 6,800/µl in long survivors, p = 0.033), higher glomerular filtration rate (39.4 vs. 29.9 ml/min/1.73 m(2), p = 0.035), had more hospitalization before starting the treatment (3.4 vs. 1.9 days per month, p = 0.003) and lower estimated left ventricular mass index (113 vs. 137 g/m(2), p = 0.035). Long-term survivors demonstrated significant improvement in the New York Heart Association functional class by a median of one class, reduced hospitalization rate by 55% and decrease in dependence on intravenous diuretics and vasoactive medications (73% drop in CHF day care visits during the first year of treatment). CONCLUSIONS: Survival of patients with refractory CHF treated with PD is highly variable. Serum sodium, serum albumin and hospitalization rate are important prognostic factors for long-term survival. Long survivors demonstrated improved functional status, reduced hospitalization and mortality rates.

Urinary organic anion transporter protein profiles in AKI.

BACKGROUND: Organic anion transporters (OATs) are located on either the basolateral or the apical membrane of the proximal tubule cell and mediate the absorption and secretion of various drugs and endogenous metabolites. It has been shown that cellular damage in acute kidney injury (AKI) involves three forms of injury: sublethal damage resulting in loss of cell polarity, cell death through apoptosis and necrosis. We hypothesize that cellular mistargeting of OAT proteins in AKI will change the profile of OAT proteins in urine. METHODS: Thirty AKI patients were included in the study. AKI was defined by clinical course, daily urine output, response to fluid repletion, urinary sediment, fractional excretion of sodium (FeNa) and urine osmolality. Urinary OAT1, OAT3 and OAT4 protein abundance was measured from semiquantitative immunoblots of urine membrane fraction samples (exosome) collected from patients with AKI and from control subjects. RESULTS: Although all patients studied reached a similar severity of renal failure measured by serum creatinine, some of them recovered from AKI with supportive care only, while others required renal replacement therapy (RRT). OAT1 and OAT3, which are normally localized in the basolateral membrane of the proximal tubule cell, were detected at low levels in urine from control subjects and were increased significantly in all patients with AKI. OAT4 protein, which is normally localized in the luminal membrane of proximal tubule cells, was present in abundance in urine of control subjects. Interestingly, in patients with AKI who eventually recovered, urinary OAT4 was found to be significantly lower than in controls, while in patients who needed RRT, it was higher than in controls. CONCLUSIONS: We have shown that OATs are mistargeted in AKI. The urinary OAT protein profile can help us to learn about the pathophysiology of the disease and might be a marker of AKI severity. AKI patients with early reversible proximal tubular damage will have high urine OAT1 and OAT3 and low OAT4, while patients with severe AKI will have high urine OAT1, OAT3 and OAT4.

Molecular study of proteinuria in patients treated with B12 supplements: do not forget megaloblastic anemia type 1.

BACKGROUND/AIMS: Current consensus supports the notion that proteinuria is a marker of renal disease with prognostic implications. Whereas most chronic kidney disease patients with proteinuria would often require antiproteinuric agents, there are some exceptions. Megaloblastic anemia type 1 (MGA1) is characterized by megaloblastic anemia due to congenital selective vitamin B(12) malabsorption and proteinuria. In the present study, we describe 2 Israeli Jewish patients with MGA1 and isolated proteinuria. METHODS: Because of their origin, the patients were screened for the presence of the already studied Tunisian AMN mutation, by direct sequencing the corresponding region from genomic DNA. PCR products were purified and sequenced. RESULTS: Genomic DNA sequencing of the AMN gene of both patients confirmed that the acceptor splice site in intron 3 was changed from CAG to CGG (208-2A→G). CONCLUSION: We determined the molecular basis of MGA1 in both patients and discuss the involvement of the cubilin/AMN complex in this pathology and its role in the development of the proteinuria. We also discuss the questionable significance of antiproteinuric treatment for these patients.

Late diagnosis of primary hyperoxaluria type 2 in the adult: effect of a novel mutation in GRHPR gene on enzymatic activity and molecular modeling.

PURPOSE: Genetic causes of nephrolithiasis are underestimated. Primary hyperoxaluria type 2 is a rare autosomal recessive disease caused by mutations in the GRHPR gene, leading to an accumulation of oxalate and L-glycerate with recurrent kidney stone formation and nephrocalcinosis, and the later development of renal failure and systemic oxalate depositions. We studied the effects of a novel GRHPR mutation on GRHPR enzymatic activity and molecular modeling. MATERIALS AND METHODS: Genomic DNA from a 50-year-old male with a late diagnosis of primary hyperoxaluria type 2 was extracted, analyzed and compared with the established human GRHPR gene sequence. Restriction enzyme analysis of the patient, 30 healthy controls and 30 patients with nephrolithiasis of various causes was done to confirm the presence of the mutation. GRHPR activity was analyzed by site directed mutagenesis of WT and mutant clones. We studied the effects of the mutation on enzymatic molecular modeling. RESULTS: We found the novel homozygous single missense mutation A975G in exon 9, creating an amino acid change from asparagine to aspartic acid in position 312. No mutations were detected in restriction enzyme analysis in all 30 healthy controls and 30 patients with nephrolithiasis of various causes. Transfected cells with the mutant clone showed abolished GRHPR activity. Molecular modeling studies revealed that the mutation was likely to disrupt the correct folding of the GRHPR substrate binding domain, hence affecting the enzyme active site. CONCLUSIONS: Primary hyperoxaluria type 2 should be considered in patients at adult stone clinics who have had a history of nephrolithiasis since childhood, especially in those with consanguineous parents. Biochemical analysis followed by mutation identification should be the approach for making the definitive diagnosis of primary hyperoxaluria type 2.

Non-urate transporter 1-related renal hypouricemia and acute renal failure in an Israeli-Arab family.

Idiopathic renal hypouricemia (IRHU) is a rare hereditary disease, predisposing the individual to exercise-induced acute renal failure (EIARF) and nephrolithiasis, and it is characterized by increased clearance of renal uric acid. Most of the described patients are Japanese, who have loss-of-function mutations in the SLC22A12 gene coding for the human urate transporter 1 (URAT1) gene. An 18-year-old youth, who was admitted for EIARF due to IRHU, and six consanguineous Israeli-Arab family members were included in the study. The family members were tested for fractional excretion of uric acid and molecular analysis of the URAT1 gene. Four family members, including the proband, had very low levels of blood uric acid and high rate of fractional excretion (FE urate> 100%) of uric acid. Genetic analysis of the affected family members did not reveal a mutation in the coding regions and intron-exon boundaries of SCL22A12. Haplotype analysis excluded SCL22A12 involvement in the pathogenesis, suggesting a different gene as a cause of the disease. We herein describe the first Israeli-Arab family with IRHU. A non-URAT1 genetic defect that causes decreased reabsorption or, more probably, increased secretion of uric acid, induces IRHU. Further studies are required in order to elucidate the genetic defect.

Truncating mutations in the chloride/proton ClC-5 antiporter gene in Seven Jewish Israeli families with Dent's 1 disease.

Dent's disease is an X-linked hereditary renal tubular disorder characterized by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and progressive renal failure. About 60% of patients have mutations in the CLCN5 gene (Dent 1), which encodes a kidney-specific chloride/proton antiporter, and 15% of patients have mutations in the OCRL1 gene (Dent 2). The aim of the study was to identify CLCN5 mutations in Jewish Israeli families with Dent's disease and to characterize the associated clinical syndromes. We studied 17 patients from 14 unrelated Israeli families with a clinical diagnosis of Dent's disease. LMWP was detected in all patients. Most of the affected individuals had hypercalciuria and nephrocalcinosis. Renal stones were found in 1 patient, and renal insufficiency developed in 2 patients. We identified six different truncating CLCN5 mutations that were segregated with the disease in 7 families: three nonsense mutations (Arg28stop, Arg467stop and Arg637stop), one deletion mutation (505delA) and two novel mutations, consisted of one deletion mutation (1493delG) and one insertion mutation (409insC). All the mutations cause premature termination of protein translation and result in a non-functional truncated protein. The clinical characteristics of patients with different mutations were, in general, similar.

Hyponatremia in refractory congestive heart failure patients treated with icodextrin-based peritoneal dialysis: A case series.

Severe congestive heart failure (CHF) patients are prone to hyponatremia. Peritoneal dialysis (PD) is increasingly used for long-term management of refractory CHF patients. The glucose polymer icodextrin was proposed to be a good option for fluid removal in such patients. A small, although statistically significant reduction in serum sodium (∼2mmol/l) consistently observed in multiple trials, is considered as not clinically relevant. Here we reported five refractory CHF patients who demonstrated sodium drop by median of 8meq/l (range 5.4-8.3meq/l) after icodextrin was added to their program. It seems that icodextrin may contribute to clinically relevant hyponatremia if the hyponatremia is compounded by other factors. Patients with extremely severe congestive heart failure are susceptible to this complication.

Inflammatory Biomarkers in Refractory Congestive Heart Failure Patients Treated with Peritoneal Dialysis.

Proinflammatory cytokines play a pathogenic role in congestive heart failure. In this study, the effect of peritoneal dialysis treatment on inflammatory cytokines levels in refractory congestive heart failure patients was investigated. During the treatment, the patients reached a well-tolerated edema-free state and demonstrated significant improvement in NYHA functional class. Brain natriuretic peptide decreased significantly after 3 months of treatment and remained stable at 6 months. C-reactive protein, a plasma marker of inflammation, decreased significantly following the treatment. Circulating inflammatory cytokines TNF-α and IL-6 decreased significantly after 3 months of peritoneal dialysis treatment and remained low at 6 months. The reduction in circulating inflammatory cytokines levels may be partly responsible for the efficacy of peritoneal dialysis for refractory congestive heart failure.

Hyponatremia in refractory congestive heart failure patients treated with icodextrin-based peritoneal dialysis: A case series / Hiponatremia en pacientes con insuficiencia cardíaca congestiva resistentes al tratamiento tratados con diálisis peritoneal con icodextrina: una serie de casos

Severe congestive heart failure (CHF) patients are prone to hyponatremia. Peritoneal dialysis (PD) is increasingly used for long-term management of refractory CHF patients. The glucose polymer icodextrin was proposed to be a good option for fluid removal in such patients. A small, although statistically significant reduction in serum sodium (∼2mmol/l) consistently observed in multiple trials, is considered as not clinically relevant. Here we reported five refractory CHF patients who demonstrated sodium drop by median of 8meq/l (range 5.4-8.3meq/l) after icodextrin was added to their program. It seems that icodextrin may contribute to clinically relevant hyponatremia if the hyponatremia is compounded by other factors. Patients with extremely severe congestive heart failure are susceptible to this complication (AU)

Los pacientes con insuficiencia cardíaca congestiva grave son propensos a sufrir hiponatremia. La diálisis peritoneal se utiliza cada vez más para el tratamiento a largo plazo de los pacientes con insuficiencia cardíaca congestiva resistentes al tratamiento. El polímero de glucosa icodextrina se propuso como una buena opción para la ultrafiltración. Una reducción pequeña, aunque estadísticamente significativa, del sodio sérico (∼2mmol/l) observada sistemáticamente en numerosos ensayos no se considera de relevancia clínica. En este documento informamos de 5 casos de pacientes con insuficiencia cardíaca congestiva resistentes al tratamiento que presentaron una caída de las concentraciones de sodio en una mediana de 8mEq/l (intervalo 5,4-8,3mEq/l) después de la adición de icodextrina a su programa. Parece ser que la icodextrina puede contribuir a una hiponatremia clínicamente relevante si se combina con otros factores. Los pacientes con insuficiencia cardíaca congestiva muy grave son propensos a esta complicación (AU)

Hyperphosphatemia during spontaneous tumor lysis syndrome culminate in severe hypophosphatemia at the time of blast crisis of Phneg CML to acute myelomoncytic leukemia.

Extreme swing of phosphor from severe hyperphosphatemia to severe hypophosphatemia in a patient with blast crisis of myeloid origin was the result of imbalance between massive apoptosis of leukemic cells in the context of spontaneous tumor lysis syndrome and massive production of leukemic cells with only 1% of blast in peripheral blood. The mutated p53 protein suggested acting as oncogene in the presented case and possibly affecting phosphor status.

A novel missense mutation in the sodium bicarbonate cotransporter (NBCe1/SLC4A4) causes proximal tubular acidosis and glaucoma through ion transport defects.

In humans and terrestrial vertebrates, the kidney controls systemic pH in part by absorbing filtered bicarbonate in the proximal tubule via an electrogenic Na+/HCO3- cotransporter (NBCe1/SLC4A4). Recently, human genetics revealed that NBCe1 is the major renal contributor to this process. Homozygous point mutations in NBCe1 cause proximal renal tubular acidosis (pRTA), glaucoma, and cataracts (Igarashi, T., Inatomi, J., Sekine, T., Cha, S. H., Kanai, Y., Kunimi, M., Tsukamoto, K., Satoh, H., Shimadzu, M., Tozawa, F., Mori, T., Shiobara, M., Seki, G., and Endou, H. (1999) Nat. Genet. 23, 264-266). We have identified and functionally characterized a novel, homozygous, missense mutation (S427L) in NBCe1, also resulting in pRTA and similar eye defects without mental retardation. To understand the pathophysiology of the syndrome, we expressed wild-type (WT) NBCe1 and S427L-NBCe1 in Xenopus oocytes. Function was evaluated by measuring intracellular pH (HCO3- transport) and membrane currents using microelectrodes. HCO3- -elicited currents for S427L were approximately 10% of WT NBCe1, and CO2-induced acidification was approximately 4-fold faster. Na+ -dependent HCO3- transport (currents and acidification) was also approximately 10% of WT. Current-voltage (I-V) analysis reveals that S427L has no reversal potential in HCO3-, indicating that under physiological ion gradient conditions, NaHCO3 could not move out of cells as is needed for renal HCO3- absorption and ocular pressure homeostasis. I-V analysis without Na+ further shows that the S427L-mediated NaHCO3 efflux mode is depressed or absent. These experiments reveal that voltage- and Na+ -dependent transport by S427L-hkNBCe1 is unfavorably altered, thereby causing both insufficient HCO3- absorption by the kidney (proximal RTA) and inappropriate anterior chamber fluid transport (glaucoma).