Showing papers by "Laura Soldati published in 2009"

Roles of calcium-sensing receptor (CaSR) in renal mineral ion transport.

Abstract: Calcium-sensing receptor (CaSR), a member of family C of the G protein-coupled receptors, is expressed most abundantly in the parathyroid glands and kidney. It plays key role in these two organs because it senses changes in extracellular calcium and regulates PTH secretion and calcium reabsorption to suit the extracellular calcium concentration. In kidney, CaSR is expressed in all nephron segments. It has an inhibitory effect on the reabsorption of calcium, potassium, sodium and water, depending on the particular function of the different tubular tracts. Among its inhibitory effects, CaSR modulates the signaling pathways used by the tubulocytes to activate electrolyte or water reabsorption. The only site where there is no such inhibitory effect is in the proximal tubule, where CaSR enhances phosphate reabsorption to counteract the effect of PTH. CaSR mutations and polymorphisms cause disorders characterized by alterations in renal excretion and serum calcium concentrations. They also can cause sodium and potassium excretion disorders. CaSR also mediates the acute adverse renal effects of hypercalcemia, which include a reduced sodium, potassium and water reabsorption. From a teleological perspective, CaSR seems to protect human tissues against calcium excess in extracellular fluids.

Novel mutations of the CLCN5 gene including a complex allele and A 5' UTR mutation in Dent disease 1.

Abstract: To the Editor : Dent disease (DD) 1 (OMIM 300009) is an X-linked disorder of renal tubular function, characterized by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis and progressive renal failure, and associated with mutations in the ClC-5 Cl−/H+ endosomal exchanger all located in the coding region of the CLCN5 gene (1, 2). We report here the identification of 15 novel mutations including a complex allele and a nucleotide substitution in the 5′UTR region of the CLCN5 gene. Thirty patients with clinical suspicion of DD were screened by single-strand conformation polymorphism (SSCP) analysis and direct sequencing for the presence of mutations in the coding sequence and the exon-intron boundaries as well as in the 5′untranslated exons of the CLCN5 gene. All the patients were of Italian origin, except 1 from the United Kingdom. Sixteen of the 30 patients presented CLCN5 mutations of which 15 were novel and 1 recurrent (S244L). The phenotypic characteristics of patients with and without CLCN5 mutations are reported in Table 1. The table shows that LMWP, hypercalciuria and nephrocalcinosis, represent the triad of manifestations most relevant for the diagnosis of DD 1. Table 2 reports the 15 novel CLCN5 mutations identified in DD patients. Each of the missense and deletion–insertion mutations predicts a structurally significant alteration to the ClC-5 Cl−/H+ exchanger, and is thus likely to be of importance in the aetiology of the disease. The three frameshift mutations, leading to premature termination codons (PTC), can induce either a truncated ClC-5 product or mRNA degradation through nonsense-mediated decay which are likely to result in a loss of antiporter function and chloride conductance. The two in-frame codon deletion and the insertion are thought to alter the ClC-5 α-helices H and I, which are two of the four major helices involved in the formation of dimer interface (3). All the missense mutations, except one located in the C-terminal domain, are at or near the ClC-5 dimer interface. Moreover they involved amino acids conserved among different species or present in all known ClCs and were predicted with a high confidence to affect protein function by both the web program SIFT (4) and PolyPhen (5). For four out of six missense mutations (W58L, G512D, V519D, P621L) and for T277_L278 ins S mutation it was possible to establish that they segregated with DD trait in family members. Three intronic mutations affecting the canonical consensus splicing donor site of intron 4, 8 and 11 were detected in three patients. In two of them, the presence of an aberrantly spliced ClC-5 mRNA in leukocytes, leading to a truncated or absent protein, confirmed the functional significance of the mutations (Fig. 1). The presence of an aberrantly spliced mRNA due to the IVS4 +4 A>G could not be proved by transcription polymerase chain reaction (RT-PCR) analysis because the patient’s RNA was not available. The Automated Splice-Site Analysis program (ASSA; (6)), however, predicts that this variant would lower the strength of the donor splice-site leading probably to exon 4 skipping. We identified a complex allele (S386F and S388fsX434) in one patient from North Italy, inherited from his mother and grandmother. Since both the web program SIFT and PolyPhen predicted that the missense mutation S386F did not affect protein function, and the search for potential exonic splicing enhancer (ESE) motifs using ESE finder (7), RESCUE-ESE (8) and ASSA did not evidence any modification, we wondered if the mutation was indeed a polymorphism. The substitution was not found in our series of 69 patients affected by DD and in 311 X chromosomes from umbilical cord DNA samples thus

Renal osteodystrophy and vascular calcification.

Abstract: Chronic kidney disease (CKD) is characterized by phosphate retention and reduced synthesis of 1.25(OH)2-vitamin D stimulating parathyroid hyperplasia. These changes cause a complex osteopathy, defined as renal osteodystrophy, and vascular calcification. Renal osteodystrophy increases the risk of fracture and causes deformities and disability. Vascular calcification occurs in a large proportion of hemodialysis patients and is a marker of arteriopathy. Calcifying arteriopathy induces arterial stiffness and contributes to the high cardiovascular mortality and morbidity among CKD patients. Vascular calcification results from a process of local bone formation induced by osteoblast-like cells developing in the vascular wall from resident cells. Osteoblast differentiation of resident vascular cells may be mediated by metabolic factors and may be induced by high concentrations of phosphate. Therefore, phosphate retention appears as the most detrimental factor affecting arteries in CKD patients. There is no specific therapy to revert soft tissue calcification, but calcification must be prevented in the early stages of CKD.

What do we know after ten years of genetic research into calcium kidney stones

Abstract: Genetic studies of calcium kidney stones have so far assessed single candidate genes by testing linkage disequilibrium or association between a locus and stone disease. They showed the possible involvement of the calciumsensing receptor gene, vitamin D receptor gene, and bicarbonate-sensitive adenylate cyclase gene. In addition to research in humans, the study of different strains of knock-out mice let us include the gene of phosphate reabsorption carrier NPT2, caveolin-1, protein NHERF-1 modulating calcium and urate reabsorption, osteopontin and Tamm-Horsfall protein among the possible determinants. However, the interactions between genes and also between environmental factors and genes are generally considered fundamental in calcium stone formation. Thus, the genetic studies carried out to date have not led to a significant growth of the knowledge about the causes of calcium kidney stones, even though they have allowed us to assess the size of the problem and define criteria to address it. Further knowledge of the causes of calcium stones may be obtained using the instruments that modern biotechnology and bioinformatics have made available to researchers.

Aspetti epidemiologici della calcolosi di calcio in Italia: distribuzione dei fenotipi intermedi nella popolazione italiana

Abstract: sono stati registrati nei pazienti con calcolosi renale calcica e potrebbero avere un’importanza patogenetica, almeno in una parte dei casi. L’elevata escrezione di sodio e fosfato, con conseguente ipofosforemia, e la ridotta escrezione di potassio sono spesso presenti nei pazienti e potrebbero essere dovuti ad abituduni dietetiche particolari (6), ma il loro significato è stato poco approfondito nella letteratura medica. Lo studio dei difetti urinari e delle relazioni tra questi difetti nei pazienti calcolotici potrebbe essere uno strumento per identificare sottogruppi di pazienti simili da un punto di vista metabolico, nutrizionale o genetico, che condividono fattori di rischio litogeno. Nonostante questa possibilità, gli studi che analizzano le caratteristiche fenotipiche dei pazienti con calcolosi renale si sono limitati a studiare le frequenze dei singoli difetti tralasciando di verificare le interrelazioni tra gli stessi e il peso dei singoli difetti nello sviluppo della calcolosi. Abbiamo perciò analizzato una popolazione italiana di Introduzione