The Expression and Implication of TRPV5,Calbindin-D28k and NCX1 in Idiopathic Hypercalciuria

The expression of calcium epithelium TRPV5, alcium binding protein Calbindin-D28k and Na＋/Ca2＋ exchanger NCX1 was detected in renal distal convoluted tubule, and their effects on urine calcium reabsorption and the possible pathogenic mechanism in idiopathic hypercalciuria （IH） were investigated. Genetic hypercalciuric stone-forming （GHS） rats were chosen as animal models to study urine calcium reabsorption and IH. The cognate female and male rats that had maximal urine calcium were matched to breed next generation. Twelve GHS rats and 12 normal control （NC） SD rats were selected. Western blot and real time quantitative PCR were used to detect the protein and gene expression of TRPV5, Calbindin-D28k and NCX1 respectively. The expression levels of TRPV5 protein and mRNA in GHS rats were significantly lower than in NC rats （P〈0.05）. Western blot revealed that the expression levels of Calbindin-D28k in GHS rats and NC rats were 0.49±0.02 and 0.20±0.01 respectively, with the difference being significant between them （P〈0.05）. By using real time quantitative PCR, it was found that there was no significant difference in Calbindin-28k mRNA expression levels between GHS rats and NC rats （P〉0.05）. There was no significant differ- ence in the NCX1 expression between GHS rats and NC rats （P〉0.05）. It was suggested that TRPV5 and Calbindin-D28k might play an important role in urine calcium reabsorption and IH, but they dif- ferently contributed to the pathogenesis： The down-regulation of TRPV5 decreases urine calcium reabsorption, directly leading to loss of the urine calcium and resulting in hypercalciuria, and the increased Calbindin-D28k expression could relieve, neutralize and decrease intracellular Ca2＋ concentration to maintain calcium balance. NCX1 is not the key protein in urine calcium reabsorption.     

The role of fibroblast growth factor 23 for hypophosphatemia and abnormal regulation of vitamin D metabolism in patients with McCune–Albright syndrome

McCune–Albright syndrome (MAS) is sometimes complicated by hypophosphatemia and abnormally low levels of 1,25(OH)₂D in the presence of hypophosphatemia. Recently, fibroblast growth factor 23 (FGF-23) was reported as a phosphaturic and a causal factor of abnormal vitamin D metabolism. This abnormal phosphate and vitamin D metabolism is well known to be found in oncogenic and X-linked hypophosphatemia. We furthermore reported increased circulating plasma FGF-23 levels in patients with oncogenic and X-linked hypophosphatemia. To determine whether FGF-23 may be involved in the pathogenesis of MAS, we measured plasma FGF-23 levels in six MAS patients. As a control for hypophosphatemia, we also investigated the plasma FGF-23 levels in two patients with hereditary hypophosphatemic rickets with hypercalciuria (HHRH). We also investigated the correlation of plasma FGF-23 levels with serum phosphate and 1,25(OH)₂D levels after short-term pamidronate therapy in three MAS patients. Plasma FGF-23 levels were significantly increased in patients with MAS compared to normal controls, whereas they were not increased in HHRH patients. Serum phosphate levels of the MAS patients were significantly lower than those observed in normal controls. Plasma FGF-23 levels showed significant negative correlation with serum phosphate concentrations. In three MAS patients, pamidronate therapy decreased plasma FGF-23 levels, which showed significant negative correlation with serum 1,25(OH)₂D concentrations. These data suggested that FGF-23 is a possible causal factor for hypophosphatemia and abnormal vitamin D metabolism in MAS.A part of this work was presented at the 25th annual meeting of the American Society for Bone and Mineral Research in Minneapolis, MN, in September 2003     

Two heterozygous mutations of CLDN16 in a Japanese patient with FHHNC

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC, MIN 248250) is a rare autosomal recessive tubular disorder that eventually progresses to renal failure. However, the progression to end-stage renal failure can vary from patient to patient. A primary defect is related to impaired tubular resorption of magnesium and calcium in the thick ascending limb of Henles loop. Recently, paracellin-1 was identified as a renal tight junction protein predominantly expressed in TAL. Mutations of its gene (CLDN16) have been shown to cause FHHNC. We describe a sporadic Japanese case of FHHNC. The male patient showed hematuria, hypercalciuria, and nephrocalcinosis at 5 years of age. Hypomagnesemia was also noticed at this time. As renal function gradually deteriorated, further evaluation was performed at 14 years of age and a diagnosis of FHHNC was made. Despite several medications (magnesium supplementation, citrate, and hydrochlorothiazide), he eventually progressed to renal insufficiency at 19 years of age. Analysis of the CLDN16 gene demonstrated two heterozygous mutations (R149Q and R216C). Mutations of the same amino acids have already been described in FHHNC and thus these mutations might be the cause of the disease in our patient. Hence, we confirm the genetic impairment of the CLDN16 gene in a Japanese patient with FHHNC.     

Reference values for urinary calcium excretion and screening for hypercalciuria in children and adolescents

Hypercalciuria is of continuing interest as on of the risk factors for stone disease in children, but the definition, incidence and pathogenesis are controversial. Therefore reference values for the urinary calcium/creatinine (Ca/Cr) ratios were established in 564 healthy children aged 6–17.9 years during the fasting state (09.00 h) and in 236 of them also in the post-absorptive state about 2 h after lunch (14.00–16.00 h). The Ca/Cr ratios in both urine specimens were independent of age and sex, rendering it possible to determine a common normal range and to calculate centiles for Ca excretion in a large sample of healthy children and adolescents. To provide information about the incidence of hypercalciuria the Ca/Cr ratios of 1013 other apparently healthy children aged 6–17.9 years were measured during the post-absorptive state on two consecutive days. In 39 (3.8%) of them, 21 girls, and 18 boys, the Ca excretion was elevated in both urine specimens. Thirtysix of these children, all presenting without renal complaints, underwent further investigations to elucidate the possible mechanisms of the hypercalciuria.On the basis of the Ca/Cr concentration during the fasting state and the calciuric response to a standardised oral Ca tolerance test the children were subclassified into three groups: (1) Absorptive hypercalciuria (AH, n=12): Increased calciuric response to the Ca load, but normal fasting Ca/Cr; (2) Renal hypercalciuria (RH, n=8): Increased Ca/Cr after Ca load and during the fasting state; (3) Normal Ca excretion during the fasting state and after the Ca tolerance test, but increased sodium excretion (dietary hypercalciuria, DH, n=16).The serum prolactin levels were increased in AH, and the serum P and tubular P reabsorption rates were decreased in RH, while the parathyroid function and bone turnover were unimpaired in all groups.The study provides evidence that the measurement of Ca/Cr ratios in untimed random urine specimens during the post-absorptive state may be a reasonable screening test for elevated Ca excretion and that idiopathic hypercalciuria seems to be as prevalent in children as it is in adults.Abbreviations Ca/Cr calcium/creatinine - AH absorptive hypercalciuria - RH renal hypercalciuria - P inorganic phosphate - AP alkaline phosphatase activity - 25OHD 25-hydroxyvitamin D - iPTH immunoreactive parathyroid hormone - cAMP cyclic adenosine-3,5-monophosphate - GFR glomerular filtration rate - DH dietary hypercalciuria - OH-P total hydroxyproline     

Autosomal recessive hypophosphataemic rickets with hypercalciuria is not caused by mutations in the type II renal sodium/phosphate cotransporter gene.

BACKGROUND: At present the genetic defect for autosomal recessive and autosomal dominant hypophosphataemic rickets with hypercalciuria (HHRH) is unknown. Type II sodium/phosphate cotransporter (NPT2) gene is a serious candidate for being the causative gene in either or both autosomal recessive and autosomal dominant HHRH. In the present study we tested this hypothesis in one autosomal recessive family. METHODS: The gene structure of human NPT2 is known. We tested the complete open reading frame in the affected siblings by polymerase chain reaction in combination with automatic DNA sequencing for the presence of mutations. RESULTS: We did not observe disease-causing mutations in the NPT2 gene of the affected siblings. A T855C polymorphism resulting in a histidine to arginine transition was present in the open reading frame of NPT2. The polymorphism was present in both affected as well as unaffected family members. CONCLUSION: The hypothesis that a defect in the NPT2 gene could be an underlying cause for autosomal recessive HHRH could not be sustained in our study.     

BMP2及Msx2在特发性高钙尿肾结石患者肾乳头组织表达的研究

目的：研究骨形态发生蛋白2（BMP2）及成骨样细胞转录因子Msx2在特发性高钙尿（IH）肾结石患者肾乳头组织中表达以及探讨其在IH患者结石形成中作用机制。方法：筛选特发性高钙尿肾结石患者8例（IH组）,排除各种已知可能影响血清钙或者尿钙的继发疾病;选择同期因肾肿瘤或非结石所致的无功能肾需行肾切除术的患者8例（NC组）。分别取16例患者肾乳头组织若干,各标本应用实时荧光定量PCR检测BMP2和Msx2mRNA的表达,并应用Westernblot测定两组蛋白质表达水平。结果：IH组BMP2的mRNA表达量为（1．491±0．121）,而NC组BMP2的tuRNA为（1．032±0．034）,两组间表达量差异有统计学意义（P〈0．05）;而1H组与NC组Msx2的mRNA表达量分别为（1．432±0．091）和（1．015±0．017）,两组数据差异有统计学意义（P〈0．05）。Westernblotting检测BMP2蛋白提示NC组和IH组蛋白质表达量分别为（1．475±0．042）和（1．681±0．153）,两组数据差异有统计学意义（P〈0．05）;测定Msx2蛋白水平表达显示NC组为（1．531±0．134）,而IH组（1．603±0．156）,两者差异无统计学意义（P〉0．05）。结论：特发性高钙尿（IH）肾结石患者肾乳头BMP2和Msx2mRNA表达增强为间质异位钙化特征,BMP2信号通路在特发性高钙尿结石患者Randall钙斑形成中具有一定作用。     

The role of vitamin D receptor gene polymorphisms in Turkish infants with urolithiasis

Polymorphisms in the vitamin D receptor (VDR) gene have recently been reported to be associated with urinary calculi in pediatric and adult cases, but no studies have looked at the youngest period of life. The purpose of this study was to investigate the role of VDR gene polymorphisms in infantile urolithiasis in a Turkish population. We compared a study group of 104 infants (55 girls and 49 boys, mean age 6.94?±?3.81 months) with a control group of 96 infants (51 girls and 45 boys, mean age 7.51?±?3.23) to evaluate their demographics and metabolic risk factors. PCR-based restriction analysis of the polymorphisms on the VDR gene (BsmI and TaqI) showed statistically significant differences between study and control groups (p?=?0.001 and 0.043, respectively). In addition, the prevalence of the BsmI genotype was significantly different between the hypercalciuric and normocalciuric stone formers (p?=?0.007). Allelic frequencies were similar between the urolithiasis and control groups (p?>?0.05). The B allele of BsmI and the A allele of ApaI were more prevalent in the hypercalciuric stone formers than in the normocalciuric stone formers (p?=?0.018 vs.0.036, respectively). These results suggest that the BsmI and TaqI VDR genotypes could be candidate genes leading to infantile urolithiasis.     

Renal dysfunction in patients with thalassaemia

Little is known about the effects of thalassaemia on the kidney. Characterization of underlying renal function abnormalities in thalassaemia is timely because the newer iron chelator, deferasirox, can be nephrotoxic. We aimed to determine the prevalence and correlates of renal abnormalities in thalassaemia patients, treated before deferasirox was widely available, using 24-h collections of urine. We calculated creatinine clearance and urine calcium-to-creatinine ratio and measured urinary β(2) -microglobulin, albumin, and protein. We used multivariate modelling to identify clinical, therapeutic, and laboratory predictors of renal dysfunction. One-third of thalassaemia patients who were not regularly transfused had abnormally high creatinine clearance. Regular transfusions were associated with a decrease in clearance (P = 0·004). Almost one-third of patients with thalassaemia had hypercalciuria, and regular transfusions were associated with an increase in the frequency and degree of hypercalciuria (P < 0·0001). Albuminuria was found in over half of patients, but was not consistently associated with transfusion therapy. In summary, renal hyperfiltration, hypercalciuria, and albuminuria are common in thalassaemia. Higher transfusion intensity is associated with lower creatinine clearance but more frequent hypercalciuria. The transfusion effect needs to be better understood. Awareness of underlying renal dysfunction in thalassaemia can inform decisions now about the use and monitoring of iron chelation.     

Autosomal-Recessive Mutations in SLC34A1 Encoding Sodium-Phosphate Cotransporter 2A Cause Idiopathic Infantile Hypercalcemia

Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D catabolizing enzyme 25-hydroxyvitamin D₃-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)₂D₃. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)₂D₃ with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.