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R V Thakker

Publications and source records attributed to R V Thakker.

At least 19 recordsLinked to original sources
PubMed2001

Menin interacts directly with the homeobox-containing protein Pem.

The tumour suppressor gene causing multiple endocrine neoplasia type 1 (MEN1) encodes a 610 amino acid protein, menin. In order to identify menin-interacting proteins we used a yeast two-hybrid assay to screen a 12.5-dpc mouse embryo library with partial menin encompassing amino acids 278 to 476. This identified a homeobox containing protein encoded by a placenta and embryonic expression gene, referred to as Pem. GST-pull-down and coimmunoprecipitation experiments confirmed the interaction. Both proteins colocalised predominantly in the nucleus but were occasionally also found in the cytoplasm. Furthermore, in situ hybridisation studies revealed similarities in their expression patterns in mouse embryos and adult tissues. In adult mice both Men1 and Pem yielded strong signals in testis, Sertoli cells and particularly in seminiferous tubules. Thus, our study has identified that menin interacts with Pem, and the high expression of these proteins in the testis suggests a role in spermatogenesis.

Animals↗
PubMed2001

Chromosomal aberrations in sporadic pituitary tumors.

Pituitary adenomas are common intracranial neoplasms that may be hormone-secreting or nonfunctional. Genetic defects associated with some pituitary tumors have been identified, although our understanding of the underlying molecular mechanisms remains incomplete. We have studied 75 sporadic pituitary tumors, representing the major clinical subtypes, by comparative genomic hybridization (CGH) with the aim of assessing for DNA copy number changes. CGH revealed chromosomal imbalances in 34 adenomas (45.3%), whereby gains were 4.9 times more frequently observed than losses. Most of the genetic alterations detected by CGH affected entire chromosomes (108/131, 82.4%). Gain of genetic material was observed predominantly on chromosomes X (24/75, 32%), 19 (12/75, 16%), 12 (6/75, 6.7%), 7 and 9 (5/75, 6.7%), whereas loss of DNA sequences most frequently affected chromosomes 11 (4/75, 5.3%), 13 and 10 (3/75, 4%). There were no significant differences in the CGH results for the individual clinical subtypes of pituitary tumors. These results reveal a nonrandom pattern of chromosomal alterations in pituitary tumors, in particular gains of entire chromosomes, and this may contribute to the development of such neoplasms.

Adenoma↗
PubMed2001

Absence of mutations in the growth hormone (GH)-releasing hormone receptor gene in GH-secreting pituitary adenomas.

OBJECTIVE: GH-releasing hormone (GHRH) is a potent stimulator of somatotroph cell proliferation and GH secretion. GHRH acts via binding to a G-protein coupled receptor (GPCR) (GHRH-R), that activates adenylyl cyclase (AC) and increases growth and function of somatotroph cells. Indeed, a subset (30--40%) of somatotrophic adenomas contain somatic mutations of the GNAS1 gene that encodes the alpha subunit of the G-protein (G(s)alpha) that stimulates AC. As activating mutations of other GPCRs cause development of endocrine tumours, we hypothesized that somatic activating mutations of the GHRH-R might provide the molecular basis for somatotroph cell proliferation in a subset of human GH-secreting pituitary adenomas. DESIGN: We analysed genomic DNA isolated from 26 somatotrophinomas, 17 of which lacked activating mutations in the GNAS1 gene. We individually amplified via polymerase chain reaction all 13 coding exons and the exon-intron boundaries of the GHRH-R gene. We used denaturing gradient gel electrophoresis to search for abnormalities in exons 1 through 11. Abnormally migrating bands were subjected to direct sequencing. Exons 12 and 13, encoding for the intracellular C-terminal domain, were subjected to direct sequencing. RESULTS: Mutations were not detected in any of the tumours, but a rare polymorphism in codon 225 corresponding to the third transmembrane domain (V225I) was discovered. CONCLUSIONS: GHRH-R mutations are absent or rare in somatotrophinomas, and other mechanisms must explain the somatotroph cell proliferation in the adenomas that lack activating mutations in the GNAS1 gene.

Adenoma↗
PubMed2001

Glomerular protein sieving and implications for renal failure in Fanconi syndrome.

BACKGROUND: Glomerular sieving coefficients (GSCs) of proteins have been measured extensively in animals but not humans. We have studied the proteinuria of Fanconi syndrome, a "knock-out" of renal tubular protein reabsorption, to estimate GSCs and detect potential contributors to development of renal failure. METHODS: Immunoassay of proteins and polypeptides in serum and urine of patients with early Dent's disease (mean GFR = 83 mL/min, range 60 to 101, N = 5), Lowe's syndrome (N = 3), and ADIF (N = 2) were used. RESULTS: Twenty-one proteins, ranging in mass from insulin (5.1 kD) and parathyroid hormone (PTH; 9.4 kD) to transferrin (78 kD) and intact IgG (160 kD), were present in Fanconi urine at> 6 to 1000-fold normal. A simple model assuming complete "knock-out" of the reuptake of each protein filtered normally by the glomerulus was applied to protein excretion by Dent's patients. GSCs were estimated for 12 plasma proteins, including albumin (7.7 +/- 0.9 x 10-5) and IgG (4.2 +/- 0.28 x 10-5; mean +/- SEM). We calculated the albumin concentration in normal glomerular filtrate to be 3.5 +/- 0.41 mg/L (53 +/- 6.4 nmol/L), consistent with studies in rat and dog. CONCLUSIONS: To our knowledge, this study provides the first estimates of human in vivo GSCs. Our model explains why tubular proteinuria of Fanconi syndrome includes proteins of mass of albumin and above as well as low-molecular-weight proteins, and further characterizes the endocytic pathway(s) believed defective in these syndromes. High urinary concentrations of potentially bioactive hormones such as PTH, insulin, IGF-1 and the chemokine monocyte chemoattractant protein-1 (MCP-1), were found; their presence in tubular fluid may contribute to the hypercalciuria, interstitial fibrosis, and the progressive renal failure of Fanconi syndromes.

Animals↗
PubMed2001

The hyperparathyroidism-jaw tumour syndrome in a Portuguese kindred.

The hyperparathyroidism-jaw tumour (HPT-JT) syndrome is an autosomal dominant disease characterized by the occurrence of parathyroid tumours and fibro-osseous tumours of the jaw bones. Some HPT-JT patients may also develop renal abnormalities, which include Wilms' tumours, hamartomas and polycystic disease. The HPT-JT gene has been mapped to chromosome 1q25-q31, and we report the clinical and genetic findings in a kindred from central Portugal. HPT-JT was observed in six members from three generations; all had primary hyperparathyroidism (five had parathyroid adenomas, one a parathyroid carcinoma). Ossifying jaw fibromas affecting the maxilla and/or mandible were observed in 5/6. Renal cysts (<2.5 cm) were observed in four. Genetic studies using 18 polymorphic loci from chromosome 1q25-q31, together with leukocyte DNA from 11 family members and tumour DNA from three parathyroids (two adenomas and one carcinoma), revealed loss of tumour heterozygosity in the parathyroid carcinoma only, and the retained haplotype was found to cosegregate with the disease in the six affected members. A new Portuguese kindred with the HPT-JT syndrome that maps to chromosome 1q25-q31 has been identified, and these findings will help in the further characterization of this inherited disorder.

Adenoma↗
PubMed2001

Mutational analysis in X-linked spondyloepiphyseal dysplasia tarda.

Spondyloepiphyseal dysplasia tarda (SEDT) is an X-linked recessive disorder characterized by short stature due to defective growth of the vertebral bodies. In addition, deformities of the femoral heads result in early onset secondary osteoarthritis of the hips. The disorder affects males only with heterozygous female carriers showing no consistent abnormalities. The gene causing SEDT, which is located on Xp22.12-p22.31, consists of 6 exons of which only exons 3, 4, 5, and 6 are translated to yield an 140 amino acid protein, referred to as SEDLIN. SEDLIN mutations have been observed in SEDT patients, and we have undertaken studies to characterize such mutations in four unrelated SEDT kindreds by DNA sequence analysis. We identified two nonsense and two intragenic deletional frameshift mutations. The nonsense mutations occurred in exons 4 (TGG-->TGA, Trp70Stop) and 6 (CGA-->TGA, Arg122Stop). Both of the intragenic deletions, which were approximately 750 bp and 1300-1445 bp in size, involved intron 5 and part of exon 6 and resulted in frameshifts that lead to premature termination (Stop) signals. Thus, all four mutations are predicted to result in truncated proteins. The results of our study expand the spectrum of SEDLIN mutations associated with SEDT, and this will help to elucidate further the role of this novel protein in the etiology of this form of osteochondrodysplasia.

Codon, Nonsense↗
PubMed2001

X-linked hypophosphatemia attributable to pseudoexons of the PHEX gene.

X-linked hypophosphatemia is commonly caused by mutations of the coding region of PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome). However, such PHEX mutations are not detected in approximately one third of X-linked hypophosphatemia patients who may harbor defects in the noncoding or intronic regions. We have therefore investigated 11 unrelated X-linked hypophosphatemia patients in whom coding region mutations had been excluded, for intronic mutations that may lead to mRNA splicing abnormalities, by the use of lymphoblastoid RNA and RT-PCRs. One X-linked hypophosphatemia patient was found to have 3 abnormally large transcripts, resulting from 51-bp, 100-bp, and 170-bp insertions, all of which would lead to missense peptides and premature termination codons. The origin of these transcripts was a mutation (g to t) at position +1268 of intron 7, which resulted in the occurrence of a high quality novel donor splice site (ggaagg to gtaagg). Splicing between this novel donor splice site and 3 preexisting, but normally silent, acceptor splice sites within intron 7 resulted in the occurrences of the 3 pseudoexons. This represents the first report of PHEX pseudoexons and reveals further the diversity of genetic abnormalities causing X-linked hypophosphatemia.

Cells, Cultured↗
PubMed2001

Somatic mutations in MEN type 1 tumors, consistent with the Knudson "two-hit" hypothesis.

MEN type 1 is an autosomal dominant disorder characterized by the combined occurrence of tumors of the parathyroids, anterior pituitary, and pancreatic islet cells. The MEN1 gene, which is located on chromosome 11q13, consists of 10 exons and encodes a 610-amino acid protein named MENIN. The observation of LOH involving 11q13 in MEN type 1 tumors and the inactivating germline mutations found in patients suggest that the MEN1 gene acts as a tumor suppressor, in keeping with the "two-hit" model of hereditary cancer. The second hit in MEN type 1 tumors typically involves large chromosomal deletions that include 11q13. However, this only represents one mechanism by which the second hit may occur, and the other mechanisms, such as intragenic deletions or point mutations that inactivate the gene, have not been reported in MEN type 1 tumors. We have therefore undertaken studies to search for such mutations in six MEN type 1 tumors (four parathyroid tumors, one insulinoma, and one lipoma) that did not have LOH at 11q13 as assessed using the flanking markers D11S480, D11S1883 and PYGM centromerically and D11S449 and D11S913 telomerically. This revealed four somatic mutations, which consisted of two missense mutations and two frameshift mutations in two parathyroid tumors, one insulinoma, and one lipoma. Thus, our results, which represent the first small intragenic somatic mutations reported in MEN type 1 tumors, provide further evidence that the role of the MEN1 gene is consistent with that of a tumor suppressor gene, as postulated by Knudson's "two-hit" hypothesis.

Adult↗
PubMed2001

Genetic contribution to bone metabolism, calcium excretion, and vitamin D and parathyroid hormone regulation.

A classical twin study was performed to assess the relative contribution of genetic and environmental factors to bone metabolism, calcium homeostasis, and the hormones regulating them. It was examined further whether the genetic effect is menopause dependent. The subjects were 2136 adult twins (98.3% female): 384 monozygotic (MZ) and 684 dizygotic (DZ) twin pairs. The intraclass correlations were calculated, and maximum likelihood model fitting was used to estimate genetic and environmental variance components. The intraclass correlations for all of the variables assessed were higher in MZ twin pairs. The heritabilities (95% CIs) obtained from model fitting for hormones regulating bone metabolism and calcium homeostasis were parathyroid hormone (PTH), 60% (54-65%); 25-hydroxyvitamin D [25(OH)D]; 43% (28-57%), 1,25-hydroxyvitamin D [1,25(OH)], 65% (53-74%); and vitamin D binding protein 62% (56-66%). The heritabilities (95% CIs) for markers of bone formation also were assessed; bone-specific alkaline phosphatase (BSAP), 74% (67-80%), and osteocalcin, 29% (14-44%); marker of bone resorption deoxypyridinoline (DPD), 58% (52-64%); and measure of calcium homeostasis 24 h urine calcium, creatinine (Cr), 52% (41-61%). The magnitude of genetic influence differed with menopause for most variables. This study provides evidence for the importance of genetic factors in determining bone resorption and formation, calcium excretion, and the hormones regulating these processes. It shows for the first time a clear genetic effect on bone resorption in premenopausal women and the regulation of PTH, vitamin D metabolism, and calcium excretion. The genes controlling bone hormones and markers are likely to be useful therapeutic and diagnostic targets.

Adolescent↗
PubMed2000

Mice lacking renal chloride channel, CLC-5, are a model for Dent's disease, a nephrolithiasis disorder associated with defective receptor-mediated endocytosis.

Nephrolithiasis (kidney stones) affects 5-10% of adults and is most commonly associated with hypercalciuria, which may be due to monogenic renal tubular disorders. One such hypercalciuric disorder is Dent's disease, which is characterized by renal proximal tubular defects that include low molecular weight proteinuria, aminoaciduria and glycosuria, together with rickets in some patients. Dent's disease is due to inactivating mutations of the renal-specific voltage-gated chloride channel, CLC-5, which is expressed in the proximal tubule, thick ascending limb and collecting duct. The subcellular localization of CLC-5 to the proximal tubular endosomes has suggested a role in endocytosis, and to facilitate in vivo investigations of CLC-5 in Dent's disease we generated mice lacking CLC-5 by targeted gene disruption. CLC-5-deficient mice developed renal tubular defects which included low molecular weight (<70 kDa) proteinuria, generalized aminoaciduria that was more pronounced for neutral and polar amino acids, and glycosuria. They also developed hypercalciuria and renal calcium deposits and some had deformities of the spine. Furthermore, endocytosis as assessed by horseradish peroxidase uptake in the proximal tubule was severely impaired in CLC-5-deficient mice, thereby demonstrating a role for CLC-5 in endosomal uptake of low molecular weight proteins. Thus, CLC-5-deficient mice provide a model for Dent's disease and this will help in elucidating the function of this chloride channel in endocytosis and renal calcium homeostasis.

Animals↗
PubMed2000

Evidence for the role of megalin in renal uptake of transthyretin.

The kidney is a major organ for uptake of the thyroid hormone thyroxine (T(4)) and its conversion to the active form, triiodothyronine. In the plasma, one of the T(4) carriers is transthyretin (TTR). In the present study we observed that TTR, the transporter of both T(4) and retinol-binding protein, binds to megalin, the multiligand receptor expressed on the luminal surface of various epithelia including the renal proximal tubules. In the kidney, megalin plays an important role in tubular uptake of macromolecules filtered through the glomerulus. To evaluate the importance of megalin for renal uptake of TTR, we performed binding/uptake assays using immortalized rat yolk sac cells with high expression levels of megalin. Radiolabeled TTR, free as well as in complex with thyroxine or retinol-binding protein, was rapidly taken up by the cells, and the uptake was strongly inhibited by a polyclonal megalin antibody and by the receptor-associated protein, a chaperone-like protein inhibiting ligand binding to megalin. In cell culture, different TTR mutations presented different levels of cell association and degradation, suggesting that the structure of TTR is important for megalin recognition. Both the apo form and the T(4)-bound form were taken up by the cells. Analysis of urine from patients with Dent's disease, a renal tubular disorder that alters receptor-mediated endocytic reabsorption of proteins, identified TTR as an abundant excreted protein. Furthermore, analysis of kidney sections of megalin-deficient mice revealed no immunohistochemical TTR labeling in intracellular vesicles in the proximal tubule cells when compared with wild type control littermates. Taken together, the present data indicate that TTR represents a novel megalin ligand of importance in the thyroid hormone homeostasis.

Animals↗
PubMed2000

GATA3 haplo-insufficiency causes human HDR syndrome.

Terminal deletions of chromosome 10p result in a DiGeorge-like phenotype that includes hypoparathyroidism, heart defects, immune deficiency, deafness and renal malformations. Studies in patients with 10p deletions have defined two non-overlapping regions that contribute to this complex phenotype. These are the DiGeorge critical region II (refs 1, 2), which is located on 10p13-14, and the region for the hypoparathyroidism, sensorineural deafness, renal anomaly (HDR) syndrome (Mendelian Inheritance in Man number 146255), which is located more telomeric (10p14-10pter). We have performed deletion-mapping studies in two HDR patients, and here we define a critical 200-kilobase region which contains the GATA3 gene. This gene belongs to a family of zinc-finger transcription factors that are involved in vertebrate embryonic development. Investigation for GATA3 mutations in three other HDR probands identified one nonsense mutation and two intragenic deletions that predicted a loss of function, as confirmed by absence of DNA binding by the mutant GATA3 protein. These results show that GATA3 is essential in the embryonic development of the parathyroids, auditory system and kidneys, and indicate that other GATA family members may be involved in the aetiology of human malformations.

Amino Acid Sequence↗
PubMed2000

Multiple endocrine neoplasia type 1.

Combined clinical and laboratory investigations of MEN-1 have resulted in an increased understanding of this disorder, which may be inherited as an autosomal dominant condition. Defining the features of each disease manifestation in MEN-1 has improved patient management and treatment and has facilitated a screening protocol. Application of the techniques of molecular biology has enabled the identification of the gene causing MEN-1 and the detection of mutations in patients. The protein encoded by the MEN1 gene has been shown to be involved in the regulation of JunD-mediated transcription, but much still remains to be elucidated. Recent advances permit the identification of mutant MEN1 gene carriers who are at a high risk for this disorder and who require regular and biochemical screening to detect the development of endocrine tumors.

Adult↗
PubMed2000

Clinical and genetic studies of CLCN5 mutations in Japanese families with Dent's disease.

BACKGROUND: Dent's disease is an X-linked renal tubular disorder that is characterized by low molecular weight proteinuria, hypercalciuria, nephrolithiasis, and renal failure. The disease is caused by inactivation of a renal chloride channel gene, CLCN5, that encodes a 746-amino acid protein with 12 to 13 transmembrane domains. The Japanese variant of Dent's disease has been observed to be less severe, and we have investigated two unrelated Japanese families for CLCN5 mutations. METHODS: Six patients from two unrelated families were studied. Leukocyte DNA from probands was used with CLCN5-specific primers for polymerase chain reaction (PCR) amplification of the coding region and exon-intron boundaries, and the DNA sequences of the products were determined to identify abnormalities in the gene. RNA extracted from the kidney, leukocytes, or urine sediments was used to characterize further the effects of the identified mutations. RESULTS: beta2-microglobulinuria was detected in five patients, hypercalciuria in two patients, nephrolithiasis in three patients (2 of whom were females), and one 51-year-old man had renal failure. Two novel CLCN5 mutations consisting of an a to g transition at the invariant ag acceptor splice site of intron 5 and an intragenic deletion that encompassed the region between intron 3 and intron 6 were identified. The acceptor splice site mutation led to the utilization of two alternative cryptic splice sites in exon 6 that resulted in a frameshift or skipping of the exon 6. The deletional mutation, which resulted in a loss of exons 4, 5, and 6, is predicted to lead to a loss of domains 1 through 4. Both mutations predict truncated chloride channels that are likely to result in a functional loss. CONCLUSIONS: The observations of renal failure in one male and nephrolithiasis in two females represent important new findings in this Japanese variant of Dent's disease that is associated with CLCN5 mutations. In addition, our study is the first to demonstrate the use of urinary sediment cells and renal tissue for the detection of CLCN5 transcript abnormalities. These results help to expand the spectrum of CLCN5 mutations associated with Dent's disease.

Adult↗
PubMed2000

Isolated hypercalciuria with mutation in CLCN5: relevance to idiopathic hypercalciuria.

UNLABELLED: Isolated hypercalciuria with mutation in CLCN5: Relevance to idiopathic hypercalciuria. BACKGROUND: Idiopathic hypercalciuria (IH) is the most common risk factor for kidney stones and often has a genetic component. Dent's disease (X-linked nephrolithiasis) is associated with mutations in the CLCN5 chloride channel gene, and low molecular weight (LMW) proteinuria was universally observed in affected males. We sought to identify mutations in CLCN5 or abnormalities in LMW protein excretion in a large group of patients with IH and in a rat model of genetic hypercalciuria. METHODS: One hundred and seven patients with IH (82 adults and 25 children) and one asymptomatic hypercalciuric man with a known inactivating mutation in CLCN5 were studied. Secondary causes of hypercalciuria were excluded in all. The excretion of retinol-binding protein and beta2-microglobulin was measured by immunoassay in 101 patients with IH. Mutation analysis of the CLCN5 gene was performed in 32 patients with IH and in the genetic hypercalciuric stone-forming (GHS) rat strain. RESULTS: LMW protein excretion was normal in 92 patients with IH, and only slight abnormalities were found in the other nine, none of whom had a mutation in CLCN5. One 27-year-old man who had a CLCN5 mutation was found to have isolated hypercalciuria without LMW proteinuria, renal failure, or other evidence of renal disease. Mutation analysis was normal in 32 patients with IH. The CLCN5 sequence was normal in the GHS rat. CONCLUSIONS: Inactivation of CLCN5 can be found in the setting of hypercalciuria without other features of X-linked nephrolithiasis. However, mutations in CLCN5 do not represent a common cause of IH.

Adolescent↗
PubMed2000

Tubular proteinuria defined by a study of Dent's (CLCN5 mutation) and other tubular diseases.

UNLABELLED: Tubular proteinuria defined by a study of Dent's ( CLCN5 mutation) and other tubular diseases. BACKGROUND: The term "tubular proteinuria" is often used interchangeably with "low molecular weight proteinuria" (LMWP), although the former implies a definite etiology. A specific quantitative definition of tubular proteinuria is needed, and we address this by studying five different renal disorders. METHODS: Tubular proteinuria was assessed by measuring urinary retinol-binding protein (RBP), beta2-microglobulin (beta2M), alpha1-microglobulin (alpha1M), and albumin in 138 patients: 26 affected males and 24 female carriers of the X-linked syndrome "Dent's disease," 6 patients with other Fanconi syndromes, 17 with distal renal tubular acidosis (dRTA), 39 with glomerulonephritis (GN), and 26 with Chinese herbs nephropathy (CHN). RESULTS: RBP was better than beta2M or alpha1M in identifying the tubular proteinuria of Dent's disease. Median urinary RBP levels in mg/mmol creatinine were: affected male Dent's, 18.2, N = 26; carrier female Dent's, 0. 30, N = 24; dRTA, 0.027, N = 17; GN, 0.077, N = 39; and normal adults, 0.0079, N = 61. Elevated urinary RBP (>0.017) and albumin < (10 x RBP) + 2 identified all patients with the LMWP of Dent's disease and clearly distinguished their LMWP from that of dRTA and GN. This is a quantitative definition of tubular proteinuria. Consistent with this definition, 80% of those patients with CHN who had an elevated RBP had tubular proteinuria. Urinary RBP and albumin in carriers of Dent's disease were strikingly correlated over a 100-fold range (R = 0.933). CONCLUSION: The combination of elevated urinary RBP (>0.017) and albumin < (10 x RBP) + 2 (mg protein/mmol creatinine) is a quantitative definition of tubular proteinuria. Furthermore, our findings suggest that a shared defect in tubular RBP and albumin reuptake causes this form of proteinuria.

Adolescent↗
PubMed2000

Pathogenesis of Dent's disease and related syndromes of X-linked nephrolithiasis.

Renal stone disease, which affects 12% of males and 5% of females by the seventh decade, occurs as an inherited disorder in 45% of patients and is most commonly associated with hypercalciuria. The biochemical basis for hereditary nephrolithiasis and hypercalciuria is unknown, and this has therefore been investigated by a "positional cloning" approach. As a first step in this approach, the chromosomal locations of two disorders referred to as Dent's disease and X-linked recessive nephrolithiasis (XRN) were determined. These two disorders, which represent unusual forms of the renal Fanconi syndrome, are characterized by a low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis and renal failure. An X-linked inheritance for XRN was established by studies of a North American kindred, and a similar inheritance for Dent's disease was indicated by the observation of a greater disease severity in males and an absence of male-to-male transmission in five British families. X-linked polymorphic genetic markers were used in linkage studies of these families, and the genes causing Dent's disease and XRN were mapped to Xp11. In addition, in one family with Dent's disease, a microdeletion involving the DNA probe M27 beta was identified. This microdeletion was further characterized by using yeast artificial chromosomes (YACs) and its size was estimated to be 515 Kb. A search for renal-expressed genes from this region identified a novel gene encoding a chloride channel (CLCN5) with similarities to a family of voltage-gated chloride channels. Molecular genetic studies of CLCN5 demonstrated that mutations, which resulted in a functional loss, were associated with Dent's disease and XRN. In addition, such CLCN5 mutations that would result in a functional loss have also been demonstrated in Japanese children with idiopathic low molecular weight proteinuria, hypercalciuria and nephrocalcinosis, and an Italian kindred with X-linked recessive hypophosphatemic rickets (XLRH) and hypercalciuria. Thus, four hereditary disorders of nephrolithiasis are due to mutations of the novel chloride channel, CLCN5.

Amino Acid Sequence↗