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.     

Molecular and clinical studies of Dent's disease in Japan: biochemical examination and renal ultrasonography do not predict carrier state

BACKGROUND: Dent's disease is an X-linked renal tubular disorder characterized by low-molecular-weight-proteinuria, hypercalciuria, nephrolithiasis and renal failure. The disease is due to inactivation of a renal chloride channel gene, CLCN5. We have investigated 3 unrelated Japanese families for CLCN5 mutations and assessed the carrier mothers biochemically and ultrasonogaraphically to ascertain whether these clinical examinations can predict the carrier state of the disease. MATERIAL AND METHODS: Twelve members from these families were studied biochemically and ultrasonographically. Leukocyte DNA from probands was used with CLCN5-specific primers for PCR amplification of the coding region and exon-intron boundaries, and the DNA sequences of the products determined to identify abnormalities in the gene. RESULTS: Three novel CLCN5 mutations consisting of a single base "A" insertion between nucleotides 590 and 591, a nonsense mutation (R28X) and a missense mutation (G506R) were exhibited. Hypophosphatemia was detected in 2 patients, beta2-microglobulinuria, alpha1-microglobulinuria, and hyperretinol binding proteinuria in 6 patients, hypercalciuria in 5 patients, decreased urine osmolality in 3 patients, and nephrocalcinosis or nephrolithiasis in 4 patients. Biochemical analysis of the urine and the renal ultrasonography in each carrier mother were completely normal. CONCLUSIONS: Neither urinary low-molecular-weight-proteins, urinary calcium to creatinine ratio, nor renal ultrasonography was predictive of carrier state in the 3 families with this disease, although each carrier mother had CLCN5 mutation. Hypophosphatemia and decreased urine osmolality might be a hint to suspect the carrier state of Dent's disease, although these findings are not found frequently.     

Hypercalciuria in patients with CLCN5 mutations

Hypercalciuria is regarded as a characteristic symptom of Dent disease, an X-linked recessive tubulopathy characterized by low molecular weight (LMW) proteinuria, nephrocalcinosis/nephrolithiasis, and progressive renal failure due to mutations in the CLCN5 gene. As the presence of hypercalciuria may affect the decision to consider a CLCN5 mutation in the differential diagnosis, the phenotypic spectrum and the relative frequency of hypercalciuria in patients with CLCN5 mutations was determined. We assessed renal calcium excretion in 34 male patients with proven CLCN5 mutations, who had been referred because of LMW proteinuria and at least one additional symptom of Dent disease. Hypercalciuria was defined as renal calcium excretion exceeding 0.1 mmol/kg per day. Data obtained were compared with all series of CLCN5-positive patients identified by a systematic literature survey. In 7 of our 19 families, at least 1 affected male had normal calcium excretion. Hypercalciuria was observed in 22 of 31 patients tested (71%) compared to 85 of 90 (94.4%) in series from Europe and North America and 74.4% from Japan. LMW proteinuria was present in all CLCN5-positive patients; 25% of the patients in European and North American series, 45% of the Japanese, and 41% in the present series had only two of the four principal symptoms of Dent disease. Therefore, a CLCN5 mutation should be considered irrespective of the presence of hypercalciuria in a patient with LMW proteinuria and one additional symptom of Dent disease.     

Expanding the phenotype of proteinuria in Dent disease. A case series

Background

Dent disease is an X-linked recessive renal tubular disorder characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure (MIM 300009). A recent case series identified four patients with CLCN5 mutations who presented with nephrotic-range proteinuria, histologic evidence of focal segmental and/or global sclerosis, and low molecular weight proteinuria.

Case-Diagnosis/Treatment

We characterize the clinical, genetic, and histopathological features of seven unrelated adolescent males with nephrotic-range proteinuria and CLCN5 mutations. Six patients underwent renal biopsy prior to assessing tubular proteinuria. All biopsied patients had either segmental sclerosis (3/6) or segmental increase in mesangial matrix (3/6). Five patients revealed some degree of foot process effacement, but only one patient biopsy revealed >50 % foot process effacement. The attenuated foot process effacement suggests the glomerulosclerosis is not due to a primary podocytopathy.

Conclusions

These data suggest that clinicians should consider a diagnostic evaluation for Dent disease in young males presenting with high-grade proteinuria.     

Chloride channel mutations in hypercalciuric kidney stone disease

Recent advances in molecular biology have characterized a new class of chloride channels that are referred to as voltage-gated chloride channels. To date, 9 such voltage-gated chloride channels have been identified in mammals. These are CLC-1 to CLC-7, CLC-Ka, and CLC-Kb, which are encoded by the genesCLCN1 toCLCN7, CLCNKA, andCLCNKB, respectively. Mutations in 2 of these genes, referred to asCLCN5 andCLCNKB, have been defined in the hypercalciuric nephrolithiasis disorders of Dent's disease and a form of Bartter's syndrome, respectively. In addition, other forms of Bartter's syndrome have been defined, with mutations involving the bumetanide-sensitive sodium-potassium-chloride cotransporter (NKCC2) and the potassium channel, ROMK. Finally, mutations of the thiazide-sensitive sodium chloride cotransporter (NCCT) are associated with Gitelman's syndrome, in which hypocalciuria and hypomagnesemia are notable features. These molecular genetic studies have increased our understanding of the renal tubular mechanisms that regulate mineral homeostasis. This paper was presented at the 2nd International Forum “The Frontiers of Nephrology,” Tokyo, May 10, 1998.     

Screening for CLCN5 mutation in renal calcium stone formers patients

Thirty-five patients (23 males and 12 females), age 35 +/- 13 years old, presenting either idiopathic calcium nephrolithiasis, nephrocalcinosis or mild renal failure with idiopathic calcium nephrolithiasis were selected for the analysis of low molecular weight proteinuria and the possible mutations occurrence in the chloride channel gene CLCN5. The urinary ratio of beta2-microglobulin and creatinine (beta2M/Cr) was very high in a transplanted woman with nephrocalcinosis (> 3.23 mg/mmol) and slightly high in five patients (> 0.052 or < 1.0 mg/mmol) with multiple urological manipulations. Other studied patients showed beta2M/Cr ratio at normal range (0.003-0.052 mg/mmol) without gender difference (p > 0.05). Mutation analysis of CLCN5 gene was performed in 26 patients of 35 selected (11 with idiopathic hypercalciuria; 6 men with normal calciuria; 3 with mild renal insufficiency and 6 with nephrocalcinosis) and was normal in all subjects even in those with abnormal molecular weight proteinuria. Conclusion: CLCN5 gene mutation is not a common cause of kidney stone disease or nephrocalcinosis in a group of Brazilian patients studied.     

Molecular analysis of the CLCN5 gene in Dent's disease: first mutation identified in a patient from South America

BACKGROUND: Dent's disease is a rare renal tubular disorder characterized by low-molecular weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and eventual renal failure. The selective loss of low-molecular weight proteins points to a defect of the proximal tubule, where filtered proteins are normally reabsorbed by endocytosis. The disease tends to present in childhood or early adult life, and males are more severely affected than females. The disease is caused by mutations in CLCN5 or OCRL1, both on the X chromosome, which code for the chloride/proton exchange transporter ClC-5 and the phosphatidylinositol-4,5-biphosphate-5-phosphatase, respectively. METHODS: Mutational analysis of CLCN5 gene from 4 unrelated patients diagnosed with Dent's disease and their relatives, 3 from Spain and 1 from Bolivia, was performed by PCR and automatic DNA sequencing. RESULTS: In the current study, we report the identification of 4 mutations in CLCN5 of 1 family from Bolivia and 3 families from Spain. Two of the mutations are novel and consist of 1 nonsense mutation, Y502X, and 1 missense mutation, L225P, affecting ClC-5alpha-helix F, one of the helices involved in formation of the chloride selectivity filter. CONCLUSIONS: Our results add to the expanding spectrum of mutations in CLCN5. This is the first report of a CLCN5 mutation in a Dent's disease patient of South American origin.     

Renal chloride channel, CLCN5, mutations in Dent's disease.

Dent's disease is an X-linked renal tubular disorder characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and renal failure. Patients with Dent's disease may also suffer from rickets and other features of the renal Fanconi Syndrome. Patients may have mutations in the X-linked renal chloride channel gene, CLCN5, which encodes a 746-amino-acid protein with 12-13 transmembrane domains. We have investigated the 11 coding exons of CLCN5 for mutations in eight unrelated patients with Dent's disease. Leukocyte DNA was used for the polymerase chain reaction amplification of CLCN5 and the products analyzed for single-stranded conformational polymorphisms (SSCPs). Abnormal SSCPs were sequenced and revealed eight mutations. These consisted of three nonsense mutations (Arg34Stop, Arg648Stop, Arg704Stop), four deletions involving codons 40, 86, 157, and 241, and one acceptor splice consensus sequence mutation tgcag --> tgaag. The mutations were confirmed either by restriction endonuclease or sequence-specific oligonucleotide hybridization analysis. In addition, an analysis of 110 alleles from 74 unrelated normal individuals demonstrated that the DNA sequence changes were not common polymorphisms. All of the mutations predict truncated chloride channels that are likely to result in a functional loss. Thus, our findings expand the spectrum of CLCN5 mutations associated with Dent's disease and the results will help to elucidate further the functional domains of this novel chloride channel.     

Phenotypic and genetic heterogeneity in Dent's disease--the results of an Italian collaborative study.

BACKGROUND: Dent's disease is an inherited tubulopathy caused by CLCN5 gene mutations. While a typical phenotype characterized by low-molecular-weight (LMW) proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and progressive renal failure in various combinations often enables a clinical diagnosis, less severe sub-clinical cases may go under-diagnosed. METHODS: By single-strand conformation polymorphism analysis and direct sequencing, we screened 40 male patients from 40 unrelated families for CLCN5 gene mutations. Twenty-four of these patients had the prominent features of Dent's disease, including LMW proteinuria, hypercalciuria and nephrocalcinosis. RESULTS: We identified 24 mutations in the CLCN5 gene in 21/24 patients with a typical phenotype and in 3/16 patients with a partial clinical picture of Dent's disease. Overall, 10 novel CLCN5 mutations were identified (E6fsX11, W58fsX97, 267 del E, Y272C, N340K, F444fsX448, W547X, Q600X, IVS3 +2 G>C and IVS3 -1 G>A), extending the number of mutations identified so far from 75 to 85. The CLCN5 coding sequence was normal in three patients. In the group with an incomplete Dent's disease phenotype, we detected two intronic mutations and one silent substitution leading to the up regulation of an alternatively spliced isoform. CONCLUSIONS: Our data confirm the genetic heterogeneity of Dent's disease. In most classic cases, the clinical diagnosis is confirmed by genetic tests.     

Novel truncating mutations in the ClC-5 chloride channel gene in patients with Dent's disease.

BACKGROUND: Dent's disease is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and eventual renal failure. The disease is caused by mutations in the X-linked chloride channel CLCN5 gene, which encodes a 746-amino-acid protein expressed in renal tubules. These mutations have been reported in unrelated families from the UK, USA, Japan and other countries. We were interested in identifying additional mutations in the CLCN5 coding region of Spanish patients with Dent's disease. METHODS: Five patients from three unrelated Spanish families were studied. Leukocyte genomic DNA from patients and their relatives was used with CLCN5-specific primers for polymerase chain reaction amplification of the coding region and exon-intron boundaries. Amplified products were analysed by single-strand conformational polymorphism analysis, DNA sequencing and restriction enzyme analysis. RESULTS: Low-molecular-weight proteinuria and hypercalciuria were detected in all the patients, nephrocalcinosis in two patients, and rickets or osteopenia in three patients. We identified three new CLCN5 mutations consisting of two nonsense mutations, Leu433Stop and Arg718Stop, and an insertional frameshift mutation, 65insT, which results in a stop at codon 98. These three mutations predict truncated ClC-5 proteins that, respectively, lack 314, 649 and 28 amino acids at the carboxy terminus, and are likely to result in loss of function. These mutations were shown to co-segregate with the disease in each of the three families. CONCLUSIONS: Our study is the first to characterize mutations in the CLCN5 gene in Spanish patients with Dent's disease and expands the spectrum of CLCN5 mutations associated with this disease.     

Dent's disease: identification of a novel mutation in the renal chloride channel CLCN5

Dent's disease is an inherited tubulopathy caused by a mutation in the CLCN5 chloride channel gene. It is characterized by low-molecular weight proteinuria, hypercalciuria, nephrolithiasis or nephrocalcinosis, rickets and eventual-progressive renal failure. Onset of clinical symptoms show a great variability, making a diagnosis at an early stage of the disease often difficult. Given the variably clinical picture, genetic analysis can provide a reliable method to confirm the diagnosis. Here, we report on the case of a patient with progressive renal failure showing signs of a tubular lesion and symptoms of Dent's disease. Although this rare disease was suspected by means of the clinical features, it was genetic analysis that confirmed the diagnosis and revealed a novel mutation in the CLCN5 gene.     

Clinical and laboratory features of Macedonian children with OCRL mutations

OCRL mutations, which are a hallmark of Lowe syndrome, have recently been found in patients with isolated renal phenotype (Dent-2 disease). In this report, we describe clinical and laboratory features in five Macedonian children with mutations in the OCRL gene. Children with a clinical diagnosis of Lowe syndrome or Dent disease underwent complete neurological and ophthalmological examination, imaging of the kidney and urinary tract, assessment of renal tubular function, and mutation analysis of the OCRL gene. Two children (18 months and 11 years, respectively) were diagnosed with Lowe syndrome on the basis of congenital cataracts, severe psychomotor retardation, and renal dysfunction. Both children had low molecular weight proteinuria (LMWP) and hypercalciuria, but not Fanconi syndrome. The older one had bilateral nephrolithiasis due to associated hypocitraturia and mild hyperoxaluria. Three children with asymptomatic proteinuria were diagnosed with Dent-2 disease; none had cataracts or neurological deficit. One child showed mild mental retardation. All had LMWP, hypercalciuria, and elevated enzymes (creatine phosphokinase, lactic dehydrogenase). All three children had an abnormal Tc-99m DMSA scan revealing poor visualization of the kidneys with a high radionuclide content in the bladder; none had nephrolithiasis or nephrocalcinosis. In conclusion, children with OCRL mutations may present with very mild phenotype (asymptomatic proteinuria with/without mild mental retardation) or severe classic oculocerebrorenal syndrome of Lowe. Elevated enzymes and abnormal results on the Tc-99m DMSA scan may be useful indicators for Dent-2 disease.     

Phenotype and genotype of Dent’s disease in three Korean boys

Dents disease is a hereditary renal tubular disorder caused by mutations of the CLCN5 gene and is clinically characterized by low molecular weight proteinuria, hypercalciuria and nephrocalcinosis. This disease has been reported in several countries. However, there are some phenotypic differences between countries, such as hypophosphatemic rickets, progressive renal failure and hematuria. In this study, phenotypes were analyzed in three Korean boys with Dents disease, and genetic diagnoses were performed using a new convenient method using peripheral blood RNA. Gene studies revealed two nonsense mutations, R637X in two patients and E609X in one patient. The phenotypes of the two patients with R637X were very similar to those of Japanese patients, i.e., they presented with asymptomatic proteinuria without rickets, renal failure or hematuria. The E609X patient was diagnosed genetically at 3 months of age before the onset of clinical symptoms because of superimposed furosemide-induced nephrolithiasis. This is the first report to characterize mutations in the CLCN5 gene in Korean patients with Dents disease, and expands the spectrum of CLCN5 mutations by reporting a novel mutation, E609X. In addition, the mutational analysis using peripheral blood RNA can be easily applied in the clinical diagnosis.     

Phenotype and genotype of Dent's disease in three Chinese boys

Aim:   Dent's disease represents a group of hereditary renal tubular disorders mainly characterized by hypercalciuria, nephrocalcinosis and low molecular weight proteinuria. The majority of patients with Dent's disease were found to carry CLCN5 gene mutations, whereas a small fraction of patients carry OCRL1 gene mutations. Up to date, over 100 patients with Dent's disease have been reported to carry CLCN5 gene mutations, but none in Chinese patients. The purpose of this study was to investigate the phenotypes and genotypes of three Chinese boys with Dent's disease.
Methods:   Three patients from three unrelated families were studied. Genomic DNA was extracted from peripheral white blood cells using a simple salting out procedure after informed consent. Thirteen pairs of primers were used to amplify all coding exons and exon–intron boundaries of the CLCN5 gene by polymerase chain reaction (PCR). All PCR products were sequenced directly on an autosequencer.
Results:   Low molecular weight proteinuria and hypercalciuria were found in all patients, nephrocalcinosis in two patients and hypophosphataemia in two patients. Three mutations of the CLCN5 gene were revealed, including R467X, L594fsX595 and R637X. Each mutation was inherited from maternal DNA, respectively. The mutation L594fsX595 was never reported before.
Conclusion:   Low molecular weight proteinuria and hypercalciuria were the main clinical features of the three Chinese boys with Dent's disease. Our study was the first to demonstrate CLCN5 gene mutations in Chinese patients with Dent's disease and we reported a novel mutation.     

Examination of megalin in renal tubular epithelium from patients with Dent disease

Dent disease is characteristic for the urinary loss of low-molecular-weight proteins and calcium, leading to renal calcification and, in some patients, chronic renal failure. This disorder is caused by loss-of-function mutations in the renal chloride channel gene, CLCN5. The animal model of this disease has demonstrated the possible role of disturbed megalin expression, which is a member of the low-density lipoprotein receptor family and is associated with renal reabsorption of a variety of proteins, in Dent disease. We examined the expression of megalin in the renal tubular epithelium of two unrelated patients with Dent disease. One patient, whose CLCN5 gene was completely deleted, showed significantly decreased staining of megalin compared with controls, while there was no change in another patient with partial deletion of the gene. These results demonstrated that mutation of CLCN5 in some patients with Dent disease may impair the expression of megalin, resulting in abnormal calcium metabolism, manifested as hypercalciuria and nephrocalcinosis.     

A novel CLCN5 mutation in a boy with Bartter-like syndrome and partial growth hormone deficiency

Dent disease is an X-linked recessive disorder affecting the proximal tubule and is characterized by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis/nephrolithiasis with a variable number of features of Fanconi syndrome. It is most often associated with mutations in CLCN5, which encodes the endosomal electrogenic chloride/proton exchanger ClC-5. Renal acidification abnormalities are only rarely seen in Dent disease, whereas the hypokalemic metabolic alkalosis associated with hyperreninemic hyperaldosteronism (Bartter-like syndrome) has been reported in only one patient so far. We report on a 5-year-old boy with Dent disease caused by mutation in CLCN5 gene, c.1073G>A, who presented with hypokalemic metabolic alkalosis and hyperreninemic hyperaldosteronism persisting over the entire follow-up. No mutations were found in NKCC2, ROMK, NCCT, or ClC-Kb genes. In addition, the patient exhibited growth failure associated with partial growth hormone (GH) deficiency. Coexistence of Bartter-like syndrome features with LMWP should prompt a clinician to search for Dent disease. The Bartter syndrome phenotype seen in Dent disease patients may represent a distinct form of Bartter syndrome, the exact mechanism of which has yet to be fully elucidated. Growth delay that persists in spite of appropriate therapy should raise suspicion of other causes, such as GH deficiency.