Search

TRPV6, a Ca-selective channel, is abundantly expressed in the placenta, intestine, kidney and bone marrow. TRPV6 is vital to Ca homeostasis and its defective expression or function is linked to transient neonatal hyperparathyroidism, Lowe syndrome/Dent disease, renal stone, osteoporosis and cancers. The fact that the molecular mechanism underlying the function and regulation of TRPV6 is still not well understood hampers, in particular, the understanding of how TRPV6 contributes to breast cancer development. By electrophysiology and Ca imaging in Xenopus oocytes and cancer cells, molecular biology and numerical simulation, here we reveal an intramolecular S5/S6 helix interaction in TRPV6 that is functionally autoinhibitory and is mediated by the R532:D620 bonding. Predicted pathogenic mutation R532Q within S5 disrupts the S5/S6 interaction leading to gain-of-function of the channel, which promotes breast cancer cell progression through strengthening of the TRPV6/PI3K interaction, activation of a PI3K/Akt/GSK-3β cascade, and up-regulation of epithelial-mesenchymal transition and anti-apoptosis., Cai et al discover an auto-inhibitory interaction between the S5 and S6 helices in the calcium-selective channel TRPV6. Molecular dynamics simulations predict that pathogenic mutation R532Q in S5 results in channel gain-of-function, which is confirmed in breast cancer migration, invasion and apoptosis assays.

Dent disease 1; Cellular models Enfermedad de Dent 1; Modelos celulares Malaltia de Dent 1; Models cel·lulars Dent disease 1 (DD1) is a rare X-linked renal proximal tubulopathy characterized by low molecular weight proteinuria and variable degree of hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressing to chronic kidney disease. Although mutations in the electrogenic Cl−/H+ antiporter ClC-5, which impair endocytic uptake in proximal tubule cells, cause the disease, there is poor genotype–phenotype correlation and their contribution to proximal tubule dysfunction remains unclear. To further discover the mechanisms linking ClC-5 loss-of-function to proximal tubule dysfunction, we have generated novel DD1 cellular models depleted of ClC-5 and carrying ClC-5 mutants p.(Val523del), p.(Glu527Asp) and p.(Ile524Lys) using the human proximal tubule-derived RPTEC/TERT1 cell line. Our DD1 cellular models exhibit impaired albumin endocytosis, increased substrate adhesion and decreased collective migration, correlating with a less differentiated epithelial phenotype. Despite sharing functional features, these DD1 cell models exhibit different gene expression profiles, being p.(Val523del) ClC-5 the mutation showing the largest differences. Gene set enrichment analysis pointed to kidney development, anion homeostasis, organic acid transport, extracellular matrix organization and cell-migration biological processes as the most likely involved in DD1 pathophysiology. In conclusion, our results revealed the pathways linking ClC-5 mutations with tubular dysfunction and, importantly, provide new cellular models to further study DD1 pathophysiology. This work was supported in part by Asdent Patients Association and grants from Ministerio de Ciencia e Innovación (SAF201459945-R and SAF201789989-R to A.M.), the Fundación Senefro (SEN2019 to A.M.) and Red de Investigación Renal REDinREN (12/0021/0013). A.M. group holds the Quality Mention from the Generalitat de Catalunya (2017 SGR).

Dent disease type 1 is caused by mutations in the CLCN5 gene that encodes CLC5, a 2Cl−/H+ exchanger. The CLC5 mutants that have been functionally analysed constitute three major classes based on protein expression, cellular localization and channel function. We tested two small molecules, 4‐phenylbutyrate (4PBA) and its analogue 2‐naphthoxyacetic acid (2‐NOAA), for their effect on mutant CLC5 function and expression by whole‐cell patch‐clamp and Western blot, respectively. The expression and function of non‐Class I CLC5 mutants that have reduced function could be restored by either treatment. Cell viability was reduced in cells treated with 2‐NOAA. 4PBA is a FDA‐approved drug for the treatment of urea cycle disorders and offers a potential therapy for Dent disease.

Dent disease is a rare genetic proximal tubulopathy which is under-recognized. Its phenotypic heterogeneity has led to several different classifications of the same disorder, but it is now widely accepted that the triad of symptoms low-molecular-weight proteinuria, hypercalciuria and nephrocalcinosis/nephrolithiasis are pathognomonic of Dent disease. Although mutations on the CLCN5 and OCRL genes are known to cause Dent disease, no such mutations are found in about 25–35% of cases, making diagnosis more challenging. This review outlines current knowledge regarding Dent disease from another perspective. Starting from the history of Dent disease, and reviewing the clinical details of patients with and without a genetic characterization, we discuss the phenotypic and genetic heterogeneity that typifies this disease. We focus particularly on all those confounding clinical signs and symptoms that can lead to a misdiagnosis. We also try to shed light on a concealed aspect of Dent disease. Although it is a proximal tubulopathy, its misdiagnosis may lead to patients undergoing kidney biopsy. In fact, some individuals with Dent disease have high-grade proteinuria, with or without hematuria, as in the clinical setting of glomerulopathy, or chronic kidney disease of uncertain origin. Although glomerular damage is frequently documented in Dent disease patients’ biopsies, there is currently no reliable evidence of renal biopsy being of either diagnostic or prognostic value. We review published histopathology reports of tubular and glomerular damage in these patients, and discuss current knowledge regarding the role of CLCN5 and OCRL genes in glomerular function.

Background Dent disease is associated with low molecular weight proteinuria and hypercalciuria and caused by pathogenic variants in either of two genes: CLCN5(Dent disease 1) and OCRL(Dent disease 2). It is generally not accompanied by extrarenal manifestations and it is difficult to distinguish Dent disease 1 from Dent disease 2 without gene testing. We retrospectively compared the characteristics of these two diseases using one of the largest cohorts to date. Methods We performed gene testing for clinically suspected Dent disease, leading to the genetic diagnosis of 85 males: 72 with Dent disease 1 and 13 with Dent disease 2. A retrospective review of the clinical findings and laboratory data obtained from questionnaires submitted in association with the gene testing was conducted for these cases. Results The following variables had significantly higher levels in Dent disease 2 than in Dent disease 1: height standard deviation score (height SDS), serum creatinine-based estimated GFR (Cr-eGFR) (median: 84 vs. 127 mL/min/1.73 m2, p < 0.01), serum aspartate aminotransferase (AST), serum alanine aminotransferase (ALT), serum lactate dehydrogenase (LDH), serum creatine phosphokinase (CK), serum potassium, serum inorganic phosphorus, serum uric acid, urine protein/creatinine ratio (median: 3.5 vs. 1.6 mg/mg, p < 0.01), and urine calcium/creatinine ratio. There were no significant differences in serum sodium, serum calcium, alkaline phosphatase (ALP), urine β2-microglobulin, incidence of nephrocalcinosis, and prevalence of intellectual disability or autism spectrum disorder. Conclusions The clinical and laboratory features of Dent disease 1 and Dent disease 2 were shown in this study. Notably, patients with Dent disease 2 showed kidney dysfunction at a younger age, which should provide a clue for the differential diagnosis of these diseases.

Background Female Dent disease 1 patients with low-molecular-weight proteinuria (LMWP) due to CLCN5 gene mutation were rarely reported, and these cases that the people were also with Turner syndrome (TS) were even hardly documented before. Case presentation Here we report a 3-year and 11-month old Chinese girl with short stature who had a karyotype of 46,X,i(X)(q10) and a de novo pathogenic variant in the CLCN5 gene on the short arm of X chromosome. Laboratory examinations showed that the patient had LMWP, hypercalciuria, hypophosphatemia, delayed bone age, and genital dysplasia. Conclusion The combination of i(X)(q10) and CLCN5 mutation causes the deletion of the wild-type CLCN5 allele that results in Dent-1 and TS. To the best of our knowledge, this is the first case that a female CLCN5 mutation hemizygote is diagnosed with Dent-1 and Turner syndrome due to isochromosome X. Also, our case has indicated that the prevalence of the situation may be largely underestimated because of the mild signs of females with Dent-1.

Dent disease is an inherited proximal renal tubulopathy leading to low molecular weight proteinuria, hypercalciuria with nephrocalcinosis and nephrolithiasis, and progressive renal failure. Two genetic mutations have been identified. The disease usually presents in childhood or early adult life and may be associated with other proximal tubular defects, which can lead to significant morbidity, especially in children. The disorder can extend to interstitial and glomerular cells, which contributes to progression to end-stage kidney disease. The pathophysiologic process remains incompletely understood, and no specific treatment is available. Dent disease is likely under-recognized. It needs to be included in the differential, especially in young males, presenting with recurrent kidney stones, proteinuria, and impaired renal function.

Dent disease is a rare X-linked renal tubulopathy due to CLCN5 and OCRL (DD2) mutations. OCRL mutations also cause Lowe syndrome (LS) involving the eyes, brain and kidney. DD2 is frequently described as a mild form of LS because some patients may present with extra-renal symptoms (ESs). Since DD2 is a rare disease and there are a low number of reported cases, it is still unclear whether it has a clinical picture distinct from LS. We retrospectively analyzed the phenotype and genotype of our cohort of 35 DD2 males and reviewed all published DD2 cases. We analyzed the distribution of mutations along the OCRL gene and evaluated the type and frequency of ES according to the type of mutation and localization in OCRL protein domains. The frequency of patients with at least one ES was 39%. Muscle findings are the most common ES (52%), while ocular findings are less common (11%). Analysis of the distribution of mutations revealed (1) truncating mutations map in the PH and linker domain, while missense mutations map in the 5-phosphatase domain, and only occasionally in the ASH-RhoGAP module; (2) five OCRL mutations cause both DD2 and LS phenotypes; (3) codon 318 is a DD2 mutational hot spot; (4) a correlation was found between the presence of ES and the position of the mutations along OCRL domains. DD2 is distinct from LS. The mutation site and the mutation type largely determine the DD2 phenotype.

Dent disease (DD) is a rare X-linked proximal tubulopathy associated with low molecular weight proteinuria (LMWP), hypercalciuria, nephrolithiasis and phosphoruria, which may progress to chronic kidney disease (CKD). About 60% of cases are caused by the mutation in CLCN5 gene. Recently, we identified a mutation in the sequence of homodimer of CLCN5 gene in a patient with DD. The Peripheral Blood Mononuclear Cells (PBMCs) of the patient were obtained and a line of induced pluripotent stem cells (iPSCs) was successfully generated. The iPSC line will be useful for further study of the pathogenesis and drug screening for DD.

Dent disease is a rare X-linked renal proximal tubulopathy presenting with low-molecular-weight proteinuria (LMWP), hypercalciuria, and nephrocalcinosis, other signs of incomplete renal Fanconi syndrome, and renal failure. Early identification of patients who harbor disease-associated mutations is important for effective medical care and avoidance of unnecessary interventions. We report the case of an asymptomatic 9-year-old boy who presented with proteinuria in routine examination. Further investigation revealed the presence of nephrotic range proteinuria, mostly LMWP and mild hypercalciuria without nephrocalcinosis, or other features of tubular dysfunction. Renal function, growth, and bone mineral density were within regular limits. The male gender and the presence of LMWP and hypercalciuria even in the absence of other findings prompted us to genetic investigation for Dent disease. A novel splice site mutation (c.416–2A > G) of the chloride voltage-gated channel 5 (CLCN5) gene, responsible for Dent disease type 1 was identified. In silico analysis revealed that this mutation interferes with the mating of exons 4 and 5. Due to early molecular diagnosis, our patient did not undergo a renal biopsy, neither required aggressive pharmacological interventions. This case underscores the diversity and complexity of CLCN5 mutations and highlights the importance of early molecular testing in male patients with incomplete phenotype of Dent disease.

Background Two interstitial microdeletions Xp11.22 including the CLCN5 and SHROOM4 genes were recently reported in a male individual affected with Dent disease, short stature, psychomotor delay and minor facial anomalies. Dent disease, characterized by a specific renal phenotype, is caused by truncating mutations of CLCN5 in the majority of affected cases. Case presentation Here, we present clinical and molecular findings in a male patient with clinical signs of Dent disease, developmental delay, short stature, microcephaly, and facial dysmorphism. Using molecular karyotyping we identified a hemizygous interstitial microdeletion Xp11.23p.11.22 of about 700 kb, which was inherited from his asymptomatic mother. Among the six deleted genes is CLCN5, which explains the renal phenotype in our patient. SHROOM4, which is partially deleted in this patient, is involved in neuronal development and was shown to be associated with X-linked intellectual disability. This is a candidate gene, the loss of which is thought to be associated with his further clinical manifestations. To rule out mutations in other genes related to intellectual disability, whole exome sequencing was performed. No other pathogenic variants that could explain the phenotypic features, were found. Conclusion We compared the clinical findings of the patient presented here with the reported case with an Xp11.22 microdeletion including CLCN5 and SHROOM4 and re-defined the phenotypic spectrum associated with this microdeletion. Electronic supplementary material The online version of this article (10.1186/s12920-018-0471-6) contains supplementary material, which is available to authorized users.

Background and Aims Hemizygous variants in chloride voltage-gated channel 5 (CLCN5) on chromosome Xp11.22 cause Dent disease type 1, characterised by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure. We describe a truncating pathogenic variant in two brothers presenting with end-stage kidney disease (ESKD) and no evidence of nephrolithiasis or nephrocalcinosis. Method Two white British brothers presented to a different regional centre over 20 years ago with ESKD of unknown aetiology. The UK 100,000 Genomes Project provided a unique opportunity to make a molecular diagnosis using whole-genome sequencing linked to clinical records. Results The older brother presented with ESKD aged 23 with bilateral small kidneys and no evidence of nephrolithiasis or nephrocalcinosis on ultrasound. He had various musculoskeletal pains, 'cutaneous ectopic calcification' and secondary hyperparathyroidism, all of which improved post parathyroidectomy. Investigation of his 17-year-old brother for consideration of kidney transplant donation revealed progressive chronic kidney disease (CKD), microscopic haematuria, proteinuria (3g/24hours) and hypokalaemia. There was no nephrocalcinosis or renal calculi on ultrasound or cystoscopy. Renal biopsy showed tubulointerstitial changes with patchy fibrosis and marked chronic inflammatory cell infiltrates. He had a history of enuresis, polydipsia, delayed bone age and general developmental delay. ESKD by the age of 22 was complicated by hypertension and hyperparathyroidism requiring parathyroidectomy. Right knee pain with 'unusual osteochondral abnormality' on MRI resulted in a supracondylar femoral osteotomy. Early serum and urine biochemistry results were not available. A hemizygous nonsense variant p.Arg417Ter in CLCN5 was identified by whole-genome sequencing via the 100,000 Genomes Project. Sanger sequencing at the Wessex Regional Genetics Laboratory confirmed this. This variant was predicted to be protein-truncating, was absent in the genome aggregation database (gnomAD) and equivalent to a variant associated with Dent disease in other patients therefore classified as a class 5 pathogenic variant according to ACMG guidelines. Three male children with Dent disease have previously been reported with the pathogenic variant p.Arg347Ter. A seven and a twelve year old from two different families in Japan had microscopic haematuria, proteinuria, elevated β2-microglobulin and normal renal function. The twelve-year-old had mild hypercalciuria, but neither had a history of nephrolithiasis or nephrocalcinosis. A four-year-old Turkish boy manifested hypophosphataemia, nephrolithiasis and nephrocalcinosis. Unusually for Dent disease, he also had hypokalaemic hypochloraemic metabolic alkalosis and hyper-reninaemic hyperaldosteronism more characteristic of Bartter syndrome, but with elevated β2-microglobulin more typical of Dent disease. None of these cases had CKD but were all reported at a very young age. Conclusion Approximately 15% of patients with ESKD in Europe have an unknown aetiology. Dent disease has a variable phenotype and screening of patients for low molecular weight proteinuria such as β2-microglobulin is not routinely performed. Dent disease type 1 should be considered in patients presenting with unexplained renal failure even without typical clinical features.

International audience; Mutations in the CLCN5 gene encoding the 2Cl- /1H+ exchanger ClC-5 are associated with Dent disease 1, an inherited renal disorder characterized by low molecular weight (LMW) proteinuria and hypercalciuria. In the kidney, ClC-5 is mostly localized in proximal tubule cells where it is thought to play a key role in the endocytosis of LMW proteins. Here, we investigated the consequences of eight previously reported pathogenic missense mutations of ClC-5 surrounding the "proton glutamate" that serves as a crucial H+ -binding site for the exchanger. A complete loss of function was observed for a group of mutants that were either retained in the endoplasmic reticulum of HEK293T cells or unstainable at plasma membrane due to proteasomal degradation. In contrast, the currents measured for a second group of mutations in X. laevis oocytes were reduced. Molecular Dynamics simulations performed on a ClC-5 homology model demonstrated that such mutations may alter ClC-5 protonation by interfering with the water pathway. Analysis of clinical data from patients harboring these mutations demonstrated no phenotype/genotype correlation. This study reveals that mutations clustered in a crucial region of ClC-5 have diverse molecular consequences in patients with Dent disease 1, ranging from altered expression to defects in transport. This article is protected by copyright. All rights reserved.

Background Dent disease is an X-linked form of progressive renal disease. This rare disorder was characterized by hypercalciuria, low molecular weight (LMW) proteinuria and proximal tubular dysfunction, caused by pathogenic variants in CLCN5 (Dent disease 1) or OCRL (Dent disease 2) genes. Fanconi syndrome is a consequence of decreased water and solute resorption in the proximal tubule of the kidney. Fanconi syndrome caused by proximal tubular dysfunction such as Dent disease might occur in early stage of the disease. Case presentation Three cases reported in this study were 3-, 10- and 14-year-old boys, and proteinuria was the first impression in all the cases. All the boys presented with LMW proteinuria and elevated urine albumin-to-creatinine ratio (ACR). Case 1 revealed a pathogenic variant in exon 11 of CLCN5 gene [NM_001127899; c.1444delG] and a nonsense mutation at nucleotide 1509 [p.L503*], and he was diagnosed as Dent disease 1. Case 2 carried a deletion of exon 3 and 4 of OCRL1 gene [NM_000276.4; c.120-238delG…A] and a nonsense mutation at nucleotide 171 in exon 5 [p.E57*], and this boy was diagnosed as Dent disease 2. Genetic analysis of Case 3 showed a missense mutation located in exon 2 of HNF4A gene [EF591040.1; c.253C > T; p.R85W] which is responsible for Fanconi syndrome. All of three pathogenic variants were not registered in GenBank. Conclusions Urine protein electrophoresis should be performed for patients with proteinuria. When patients have LMW proteinuria and/or hypercalciuria, definite diagnosis and identification of Dent disease and Fanconi syndrome requires further genetic analyses.

The various forms of Fanconi renotubular syndromes (FRTS) offer significant challenges for clinicians and present unique opportunities for scientists who study proximal tubule physiology. This review will describe the clinical characteristics, genetic underpinnings, and underlying pathophysiology of the major forms of FRST. Although the classic forms of FRTS will be presented (e.g., Dent disease or Lowe syndrome), particular attention will be paid to five of the most recently discovered FRTS subtypes caused by mutations in the genes encoding for L-arginine:glycine amidinotransferase ( GATM), solute carrier family 34 (type Ii sodium/phosphate cotransporter), member 1 ( SLC34A1), enoyl-CoAhydratase/3-hydroxyacyl CoA dehydrogenase ( EHHADH), hepatocyte nuclear factor 4A ( HNF4A), or NADH dehydrogenase complex I, assembly factor 6 ( NDUFAF6). We will explore how mutations in these genes revealed unexpected mechanisms that led to compromised proximal tubule functions. We will also describe the inherent challenges associated with gene discovery studies based on findings derived from small, single-family studies by focusing the story of FRTS type 2 ( SLC34A1). Finally, we will explain how extensive alternative splicing of HNF4A has resulted in confusion with mutation nomenclature for FRTS type 4.

The gene mutations of the chloride channel gene (CLCN5) can lead to the inherited X-linked Dent disease (X-Dent). The urine cells of a 4-year-old male X-Dent patient with the hemizygous CLCN5 gene mutation p.R718* (c.2152C > T) were reprogrammed into induced pluripotent stem cells (iPSCs) using integration free Sendai virus reprogramming system. The generated iPSCs stably expressed pluripotent stem cell markers and can be induced to differentiate into three germ layers in vitro. The karyotype of the generated iPSCs was normal (46, XY).

Lowe syndrome is a condition that primarily affects eyes, brain, and kidneys. This disorder follows X-linked recessive mode of inheritance and it occurs in males mainly. Mutations in OCRL (located at Xq25) gene can cause accumulation of phosphatidylinositol bisphosphate and disturbed actin cytoskeleton remodeling. There are 268 mutations in OCRL gene causing Lowe syndrome or Dent disease 2 in HGMD database, however 10 - 20% of Lowe syndrome suspects remain undiagnosed at molecular level. Here we present a male case of Lowe syndrome with characteristic features. Comprehensive clinical examination and genetic counseling were performed. Sanger sequencing was employed to investigate the possible OCRL mutations and we identified a donor splice site variant (NM-000276: c.2469 + 1G > A) in hemizygous state. This is a pathogenic variant according to the ACMG standards and guidelines and might explain the clinical features of the patient. This result is in accordance with the clinical diagnosis of Lowe syndrome and it is absent from ExAC, 1000 G, Iranome, GME, gnomAD Genome databases of healthy controls. In-silico analysis of this splicing variant revealed that the position is highly conserved between species. Splicing prediction tools predicted some changes in splicing pattern of the OCRL transcript, elimination of some protein features, and malfunctioning the OCRL protein as a consequence of this variant. Accordingly, we proposed the c.2469 + 1G > A variant might explain the clinical features in studied patient and be employed for prenatal diagnosis of Lowe syndrome in the family.

Background Psoriasis is a chronic inflammatory dermatosis with complex genetic basis supported by family investigation. Renal involvement in psoriasis is sparsely studied and its pathogenesis is still unclear. Methods and Results We describe the case of a 7‐year‐old boy presented new onset of nephropathy two weeks after a flare‐up of psoriasis. His mother had a long history of psoriasis without abnormal urinalysis records. The case showed non‐nephrotic range proteinuria, microscopic hematuria without any other abnormal results including renal function, complement cascade, and ultrasound. Renal pathological demonstrated the diagnosis of C3 glomerulonephritis (C3GN) showing mesangial proliferative glomerulonephritis with C3 staining only, effacement of podocyte process and intramembranous electron dense deposit by electric microscopy. Parent‐child trio WES performed to screening the common variants of psoriasis susceptibility locus and also the rare variants associated with C3GN. We identified a missense single nucleotide polymorphism of CARD14 (*607211, rs34367357, p.Val585Ile) carried by the proband and his mother. Meta‐analysis proved the association of rs34367357 and psoriasis (p = 0.006, OR = 1.23). A hemizygouse mutation of CLCN5 (*300008, c.1904A＞G,p.Asn635Ser) was identified for diagnosis of Dent disease (*300009). Conclusion The case highlights the genetic study is necessary to facilitate disease differentiation in new onset of nephropathy with psoriasis in children., A case of a 7‐year old boy presented new onset of nephropathy two weeks after a flare‐up of psoriasis. Pathological findings and genetic study identified the diagnosis of C3 glomerulonephritis with psoriasis accompanied by Dent disease.

Background Lowe syndrome (LS) is caused by loss-of-function mutations in the X-linked gene OCRL, which codes for an inositol polyphosphate 5-phosphatase that plays a key role in endosome recycling, clathrin-coated pit formation, and actin polymerization. It is characterized by congenital cataracts, intellectual and developmental disability, and renal proximal tubular dysfunction. Patients are also at high risk for developing glaucoma and seizures. We recently developed induced pluripotent stem cell (iPSC) lines from three patients with LS who have hypomorphic variants affecting the 3′ end of the gene, and their neurotypical brothers to serve as controls. Methods In this study, we used RNA sequencing (RNA-seq) to obtain transcriptome profiles in LS and control neural progenitor cells (NPCs). Results In a comparison of the patient and control NPCs (n = 3), we found 16 differentially expressed genes (DEGs) at the multiple test adjusted p value (padj) p value Conclusion Overall, the RNA-seq findings present several candidate genes that could help explain the underlying basis for the neurodevelopmental and eye problems seen in boys with LS.

Background To characterize the phenotypic spectrum and assess the antialbuminuric response to angiotensin converting enzyme (ACE) inhibitor and/or angiotensin receptor blocker (ARB) therapy in a cohort of children with Dent disease. Methods The patients’ clinical findings, renal biopsy results, genetic and follow‐up data were analyzed retrospectively. Mutations in CLCN5 or OCRL were detected by next‐generation sequencing or Sanger sequencing. Results Of 31 Dent disease boys, 24 carried CLCN5 and 7 carried OCRL mutations. Low molecular weight proteinuria and albuminuria were detected in all cases. Nephrotic‐range proteinuria and severe albuminuria were identified in 52% and 62% of cases, respectively; by 7 years of age, 6 patients had hematuria and nephrotic‐range proteinuria, and 7 patients had hematuria and moderate to severe albuminuria. In addition to disease‐related renal features, patients with Dent‐1 disease also presented with congenital cataract (1/9) and developmental delay (2/7). Seventeen of 31 patients underwent renal biopsy. Glomerular changes included mild glomerular lesions, mesangial proliferative glomerulonephritis and focal segmental glomerular sclerosis. Thirteen of the 31 patients had follow‐up records and received ACE inhibitor and/or ARB treatment for more than 3 months. After a median 1.7 (range 0.3–8.5) years of treatment, a reduction in the urinary microalbumin‐to‐creatinine ratio was observed in 54% of children. Conclusions Hematuria with nephrotic‐range proteinuria or moderate to severe albuminuria was common in Dent disease patients. Extrarenal manifestations were observed in Dent‐1 patients, which extends the phenotypic spectrum. In addition, ACE inhibitors and ARBs are well tolerated, and they are partially effective in controlling albuminuria., Hematuria with nephrotic‐range proteinuria or moderate to severe albuminuria was common in Dent disease patients.Patients with Dent‐1 disease may also present with congenital cataract and developmental delay.The percentage of urinary albumin in the total protein ranged from 24.2% to 47.6%; it was usually smaller than that of LMW proteinuria. ACE inhibitors and ARBs are partially effective in controlling albuminuria and they are well tolerated.

Proteinuria is a well-known risk factor, not only for renal disorders, but also for several other problems such as cardiovascular diseases and overall mortality. In the kidney, the chloride channel Cl(−)/H(+) exchanger C1C-5 encoded by the CLCN5 gene is actively involved in preventing protein loss. This action becomes evident in patients suffering from the rare proximal tubulopathy Dent disease because they carry a defective C1C-5 due to CLCN5 mutations. In fact, proteinuria is the distinctive clinical sign of Dent disease, and mainly involves the loss of low-molecular-weight proteins. The identification of CLCN5 disease-causing mutations has greatly improved our understanding of C1C-5 function and of the ClC-5-related physiological processes in the kidney. This review outlines current knowledge regarding the CLCN5 gene and its protein product, providing an update on C1C-5 function in tubular and glomerular cells, and focusing on its relationship with proteinuria and Dent disease.

Dent disease (DD), an X-linked renal tubulopathy, is mainly caused by loss-of-function mutations in CLCN5 (DD1) and OCRL genes. CLCN5 encodes the ClC-5 antiporter that in proximal tubules (PT) participates in the receptor-mediated endocytosis of low molecular weight proteins. Few studies have analyzed the PT expression of ClC-5 and of megalin and cubilin receptors in DD1 kidney biopsies. About 25% of DD cases lack mutations in either CLCN5 or OCRL genes (DD3), and no other disease genes have been discovered so far. Sanger sequencing was used for CLCN5 gene analysis in 158 unrelated males clinically suspected of having DD. The tubular expression of ClC-5, megalin, and cubilin was assessed by immunolabeling in 10 DD1 kidney biopsies. Whole exome sequencing (WES) was performed in eight DD3 patients. Twenty-three novel CLCN5 mutations were identified. ClC-5, megalin, and cubilin were significantly lower in DD1 than in control biopsies. The tubular expression of ClC-5 when detected was irrespective of the type of mutation. In four DD3 patients, WES revealed 12 potentially pathogenic variants in three novel genes (SLC17A1, SLC9A3, and PDZK1), and in three genes known to be associated with monogenic forms of renal proximal tubulopathies (SLC3A, LRP2, and CUBN). The supposed third Dent disease-causing gene was not discovered.

Loss-of-function mutations in the OCRL gene, which encodes the phosphatidylinositol [PI] 4,5-bisphosphate [PI(4,5)P2] 5-phosphatase OCRL, cause defective endocytosis and proximal tubule dysfunction in Lowe syndrome and Dent disease 2. The defect is due to increased levels of PI(4,5)P2 and aberrant actin polymerization, blocking endosomal trafficking. PI 3-phosphate [PI(3)P] has been recently identified as a coactivator with PI(4,5)P2 in the actin pathway. Here, we tested the hypothesis that phosphoinositide 3-kinase (PI3K) inhibitors may rescue the endocytic defect imparted by OCRL loss, by rebalancing phosphoinositide signals to the actin machinery. The broad-range PI3K inhibitor copanlisib and class IA p110α PI3K inhibitor alpelisib reduced aberrant actin polymerization in OCRL-deficient human kidney cells in vitro. Levels of PI 3,4,5-trisphosphate, PI(4,5)P2 and PI(3)P were all reduced with alpelisib treatment, and siRNA knockdown of the PI3K catalytic subunit p110α phenocopied the actin phenotype. In a humanized OcrlY/- mouse model, alpelisib reduced endosomal actin staining while restoring stress fiber architecture and levels of megalin at the plasma membrane of proximal tubule cells, reflected by improved endocytic uptake of low molecular weight proteins in vivo. Thus, our findings support the link between phosphoinositide lipids, actin polymerization and endocytic trafficking in the proximal tubule and represent a proof-of-concept for repurposing alpelisib in Lowe syndrome/Dent disease 2., Graphical abstract

We present a case of Dent disease caused by a novel intronic mutation, 1348-1G>A, of the chloride voltage-gated channel 5 (CLCN5) gene. Cultured proximal tubule cells obtained from the patient showed impaired acidification of the endosome and/or lysosome, indicating that the 1348-1G>A mutation was indeed the cause of Dent disease. Although the prevalence of osteomalacia in Dent disease is low in Japan, several factors-including poor medication adherence-caused severe osteomalacia in the current case. Oral supplementation with calcium and native/active vitamin D therapy, with careful attention to medication adherence, led to the improvement of the patient's bone status.

International audience; Dent disease is an X‐linked recessive renal tubular disorder characterized by low‐molecular‐weight proteinuria, hypercalciuria, nephrolithiasis, nephrocalcinosis, and progressive renal failure. Inactivating mutations of CLCN5, the gene encoding the 2Cl−/H+ exchanger ClC‐5, have been reported in patients with Dent disease 1. In vivo studies in mice harboring an artificial mutation in the “gating glutamate” of ClC‐5 (c.632A > C, p.Glu211Ala) and mathematical modeling suggest that endosomal chloride concentration could be an important parameter in endocytosis, rather than acidification as earlier hypothesized. Here, we described a novel pathogenic mutation affecting the “gating glutamate” of ClC‐5 (c.632A>G, p.Glu211Gly) and investigated its molecular consequences. In HEK293T cells, the p.Glu211Gly ClC‐5 mutant displayed unaltered N‐glycosylation and normal plasma membrane and early endosomes localizations. In Xenopus laevis oocytes and HEK293T cells, we found that contrasting with wild‐type ClC‐5, the mutation abolished the outward rectification, the sensitivity to extracellular H+ and converted ClC‐5 into a Cl− channel. Investigation of endosomal acidification in HEK293T cells using the pH‐sensitive pHluorin2 probe showed that the luminal pH of cells expressing a wild‐type or p.Glu211Gly ClC‐5 was not significantly different. Our study further confirms that impaired acidification of endosomes is not the only parameter leading to defective endocytosis in Dent disease 1.

The pattern of X-chromosome inactivation (XCI) can affect the clinical severity of X-linked disorders in females. XCI pattern analysis has been conducted mainly by HUMARA assay, a polymerase chain reaction-based assay using a methylation-sensitive restriction enzyme. However, this assay examines the XCI ratio of the androgen receptor gene at the genomic DNA level and does not reflect the ratio of either targeted gene directly or at the mRNA level. Here, we report four females with Dent disease, and we clarified the correlation between XCI and female cases of Dent disease using not only HUMARA assay but also a novel analytical method by RNA sequencing. We constructed genetic analysis for 4 female cases showing high level of urinary low-molecular-weight proteinuria and their parents. Their XCI pattern was analyzed by both HUMARA assay and an ultra-deep targeted RNA sequencing of the CLCN5 gene using genomic DNA and mRNA extracted from both leukocytes and urine sediment. All four cases possessed pathogenic variants of the CLCN5 gene. XCI analysis revealed skewed XCI in only two cases, while the other two showed random XCI. All assay results of HUMARA and targeted RNA sequencing in both leukocytes and urinary sediment were clearly identical in all four cases. We developed a novel XCI analytical assay of ultra-deep targeted RNA sequencing and revealed that skewed XCI explains the mechanism of onset of female Dent disease in only half of such cases.

Dent’s disease is an X-linked proximal tubulopathy characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, and progression to chronic kidney failure. The disease is caused by mutations in CLCN5 or OCRL genes and affects males, whereas female carriers are generally asymptomatic. THE AIM: to study phenotype and genotype of patients’ mothers with Dent’s disease to exclude asymptomatic carrier of CLCN5 or OCRL gene mutations responsible for X-linked tubulopathy development. PATIENTS AND METHODS . We conducted clinical and molecular-genetic study of 9 mothers of 10 boys with Dent’s disease from 8 unrelated families. Direct Sanger sequencing of CLCN5 and OCRL genes were carried out with genomic DNA of all patients and their mothers. RESULTS . Carrier status of Dent’s disease 1 (n=7) and 2 types (n=2) was confirmed in all patients’ mothers. The most prevalent features of Dent’s disease in probands’ mothers were decrease in phosphate reabsorption, hypophosphatemia, medullary nephrocalcinosis and progression to CKD 2 stage. Low molecular weight proteinuria and hypercalciuria were rare revealed in carrier females. Full phenotype of Dent’s disease discovered in 2 cousins females carrier for Dent’s disease 1 type. CONCLUSION . We found that all carrier females had phenotypic variation of Dent disease’ symptoms. We speculate that revealed phenotype in carrier females for Dent disease might be a consequence of autosome translocation or nonrandom X chromosome inactivation. These data suggest that clinicians should consider a diagnostic evaluation of mothers of boys with Dent’s disease to determine phenotype and early prevention of progression to chronic kidney disease.

Dent disease is a rare X-linked tubulopathy caused by mutations in the endosomal chloride-proton exchanger (ClC-5) resulting in defective receptor-mediated endocytosis and severe proximal tubule dysfunction. Bone marrow transplantation has recently been shown to preserve kidney function in cystinosis, a lysosomal storage disease causing proximal tubule dysfunction. Here we test the effects of bone marrow transplantation in Clcn5 Y/- mice, a faithful model for Dent disease. Transplantation of wild-type bone marrow in Clcn5 Y/- mice significantly improved proximal tubule dysfunction, with decreased low-molecular-weight proteinuria, glycosuria, calciuria, and polyuria four months after transplantation, compared to Clcn5 Y/- mice transplanted with ClC-5 knockout bone marrow. Bone marrow–derived cells engrafted in the interstitium, surrounding proximal tubule cells, which showed a rescue of the apical expression of ClC-5 and megalin receptors. The improvement of proximal tubule dysfunction correlated with Clcn5 gene expression in kidneys of mice transplanted with wild-type bone marrow cells. Coculture of Clcn5 Y/- proximal tubule cells with bone marrow–derived cells confirmed rescue of ClC-5 and megalin, resulting in improved endocytosis. Nanotubular extensions between the engrafted bone marrow–derived cells and proximal tubule cells were observed in vivo and in vitro . No rescue was found when the formation of the tunneling nanotubes was prevented by actin depolymerization or when cells were physically separated by transwell inserts. Thus, bone marrow transplantation may rescue the epithelial phenotype due to an inherited endosomal defect. Direct contacts between bone marrow–derived cells and diseased tubular cells play a key role in the rescue mechanism.

Dent disease is an X-linked recessive proximal tubular disorder that affects mostly male patients in childhood or early adult life, caused by mutations in CLCN5 (Dent disease 1) or OCRL (Dent disease 2) genes, respectively. It presents mainly with hypercalciuria, low-molecular-weight proteinuria, nephrocalcinosis and progressive renal failure. We report here the same CLCN5 mutation but different phenotypes in two Chinese brothers, and speculate on the possible reasons for the variability of the genotype-phenotype correlations.

Dent's disease-1 (CLCN5 gene) is a rare X-linked recessive tubulopathy characterized by low molecular weight proteinuria, hypercalciuria, nephrolcalcinosis or nephrolithiasis, proximal tubular dysfunction and renal failure in adulthood. Females are carriers and usually mildly affected. We present an 11-year-old child with nephrocalcinosis and nephrolithiasis with c.2010delG (or p.Asp671fs) mutation in CLCN5 gene which had not previously been reported in the Dent's disease-1. © 2018 National Academy of Pediatric Science and Innovation. All rights reserved.

Background Dent disease is an X-linked inherited renal disease that occurs almost exclusively in males. Abnormal CLC-5 function might play a role in the development of Dent disease, but the genetic interaction changes and biomarkers in Dent disease are not fully understood. The aim of this study was to explore the potential key gene biomarkers and pathways related to Dent disease in CLCN5 knockout mice model.Methods The gene expression profile GSE10162 was analyzed differentially expressed genes (DEGs), between 3 samples of CLC-5 transporter gene knockout mouse model of Dent disease and 3 samples from wild type mouse. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were applied for the enriched pathway by the online tool DAVID. A protein-protein interaction (PPI) network of DEGs was constructed to find the hub genes by STRING, and visualized with Cytoscape software.Results Three samples from were incorporated into this study. A total of 500 DEGs were filtered, consisting of 231 upregulated genes and 269 downregulated genes. GO analysis indicated that the up-regulated DEGs were significantly enriched in the regulation of transcription form RNA, regulation of cell proliferation, and ion transport, whereas down-regulated genes were mainly enriched in oxidation-reduction process, and metabolic process. KEGG analysis demonstrated that the DEGs were enriched in the metabolic pathways, neuroactive ligand-receptor interaction, nicotine addiction, morphine addiction, fatty acid elongation, TNF signaling pathway, calcium signaling pathway, and cAMP signaling pathway. PPI network analysis found 17 hub genes with greater than 10 degrees of connectivity. The hub genes might participate in TNF signaling pathway, fat digestion and absorption, and enrich in lipid metabolic process, regulation of blood pressure, cellular response to hypoxia, positive regulation of angiogenesis, positive regulation of developmental growth, and positive regulation of cytosolic calcium ion concentration.Conclusions Our study suggests that Apob, Lep, C3, Cxcl1, Acly and Mmp9 may play key roles in the progression of Dent disease. Blood lipid profiles and calcium levels might be potential prognostic biomarkers for Dent disease.

Dent disease is a rare X-linked recessive inherited tubular disease. In this multicenter study, the clinical presentation and genetic background of Chinese children with Dent disease are studied to improve the cognition and diagnostic ability of pediatricians. In this prospective cohort, we described the genotype and phenotype of a national cohort composed of 45 pediatric probands with Dent disease belonging to 45 families from 12 different regions of China recruited from 2014 to 2018 by building up the multicenter registration system. The CLCN5 gene from 32 affected families revealed 28 different mutations. The OCRL gene from 13 affected families revealed 13 different mutations. The incidence of low-molecular-weight proteinuria (LMWP) in both Dent disease type 1 populations and Dent disease type 2 populations was 100.0%; however, the incidence of other manifestations was not high, which was similar to previously reported data. Therefore, LMWP is a key clinical feature that should alert clinicians to the possibility of Dent disease. A high amount of LMWP combined with positive gene test results can be used as the diagnostic criteria for this disease. The diagnostic criteria are helpful in reducing the missed diagnosis of this disease and are beneficial for protecting the renal function of these patients through early diagnosis and early intervention.

Dent disease is a rare tubulopathy characterized by manifestations of proximal tubular dysfunction, which occurs almost exclusively in males. It mainly presents symptoms in early childhood and may progress to end-stage renal failure between the 3rd and 5th decades of human life. According to its various genetic basis and to clinical signs and symptoms, researchers define two forms of Dent disease (Dent diseases 1 and 2) and suggest that these forms are produced by mutations in the CLCN5 and OCRL genes, respectively. Dent diseases 1 and 2 account for 60% and 15% of all Dent disease cases, and their genetic cause is generally understood. However, the genetic cause of the remaining 25% of Dent disease cases remains unidentified. All relevant peer-reviewed original articles published thus far have been screened out from PubMed and have been referenced. Genetic testing has been used greatly to identify mutation types of CLCN5 and OCRL gene, and next-generation sequencing also has been used to identify an increasing number of unknown genotypes. Gene therapy may bring new hope to the treatment of Dent disease. The abuse of hormones and immunosuppressive agents for the treatment of Dent disease should be avoided to prevent unnecessary harm to children. The current research progress in classification, genetic heterogeneity, diagnosis, and treatment of Dent disease reviewed in this paper enables doctors and researchers to better understand Dent disease and provides a basis for improved prevention and treatment.

To describe the clinical and genotypic features of Dent disease in children diagnosed at our center over a period of 10 years. Case series. Pediatric Nephrology Clinic at a referral center in Northern India. The medical records of patients with Dent disease diagnosed and followed up at this hospital from June 2005 to April 2015 were reviewed. The diagnosis of Dent disease was based on presence of all three of the following: (i) low molecular weight proteinuria, (ii) hypercalciuria and (iii) one of the following: nephrolithiasis, hematuria, hypophosphatemia or renal insufficiency, with or without mutation in CLCN5 or OCRL1 genes. The phenotype in 18 patients diagnosed with Dent disease during this period was characterized by early age at onset (median 1.8 y), and polyuria, polydipsia, salt craving, hypophosphatemic rickets and night blindness. Rickets was associated with severe deformities, fractures or loss of ambulation in six patients. Nephrocalcinosis was present in three patients, while none had nephrolithiasis. Generalized aminoaciduria was seen in 13 patients, two had glucosuria alone, and one had features of Fanconi syndrome. Over a median follow up of 2.7 years, one patient developed renal failure. Genetic testing (n=15) revealed 5 missense mutations and 3 nonsense mutations in CLCN5 in 13 patients. Five of these variations (p.Met504Lys, p.Trp58Cys, p.Leu729X, p.Glu527Gln and p.Gly57Arg) have not been reported outside the Indian subcontinent. Our findings suggest a severe phenotype in a cohort of Indian patients with Dent disease.

Dent disease 1 is a rare cause of chronic kidney disease (CKD) in childhood secondary to mutations in the gene encoding the chloride–proton exchanger, CLC-5, which is found mainly in the proximal tubule. Clinical manifestations are variable and there are no known genotype–phenotype correlations. The proband was identified as having a mutation in CLCN5. The extended family of the proband was invited to participate in a study of Dent disease after several males were noted to have a history of CKD. Urine retinol binding protein, urine calcium, serum creatinine, and DNA samples were collected for analysis. Ten hemizygous males and 6 heterozygous females were identified. Advanced CKD was detected in 3 males (1 child). Renal biopsies in 4 children showed both glomerular and tubulo-interstitial changes. There was no correlation between age and disease severity. This is the first reported family from the southern hemisphere with this condition. A novel CLCN5 mutation is described, c.1618G>C (p.Ala540Pro). The severity of renal disease varies greatly among individuals.

Dent's disease is characterized by defective endocytosis in renal proximal tubules (PTs) and caused by mutations in the 2Cl(-)/H(+) exchanger, CLC-5. However, the pathological role of endosomal acidification in endocytosis has recently come into question. To clarify the mechanism of pathogenesis for Dent's disease, we examined the effects of a novel gating glutamate mutation, E211Q, on CLC-5 functions and endosomal acidification. In Xenopus oocytes, wild-type (WT) CLC-5 showed outward-rectifying currents that were inhibited by extracellular acidosis, but E211Q and an artificial pure Cl(-) channel mutant, E211A, showed linear currents that were insensitive to extracellular acidosis. Moreover, depolarizing pulse trains induced a robust reduction in the surface pH of oocytes expressing WT CLC-5 but not E211Q or E211A, indicating that the E211Q mutant functions as a pure Cl(-) channel similar to E211A. In HEK293 cells, E211A and E211Q stimulated endosomal acidification and hypotonicity-inducible vacuolar-type H(+)-ATPase (V-ATPase) activation at the plasma membrane. However, the stimulatory effects of these mutants were reduced compared with WT CLC-5. Furthermore, gene silencing experiments confirmed the functional coupling between V-ATPase and CLC-5 at the plasma membrane of isolated mouse PTs. These results reveal for the first time that the conversion of CLC-5 from a 2Cl(-)/H(+) exchanger into a Cl(-) channel induces Dent's disease in humans. In addition, defective endosomal acidification as a result of insufficient V-ATPase activation may still be important in the pathogenesis of Dent's disease.

Dent's disease is an X-linked recessive proximal tubular disorder that mostly affects male patients in childhood or early adult life. The condition is caused by mutations in the CLCN5 (Dent disease 1) or OCRL (Dent disease 2) genes located on chromosome Xp11.22 and Xq25, respectively. In most male patients, proteinuria is subnephrotic but may reach nephrotic levels. Here, we report the first case of Dent's disease complicated by nephrotic syndrome. Dent's disease should be considered in the differential diagnosis of nephrotic syndrome, and especially in male patients with early onset of nephrotic syndrome. A urinary α1-microglobulin/albumin ratio > 1 may provide the first clue to a tubulopathy.

Dent disease classically combines low-molecular-weight proteinuria, hypercalciuria with nephrocalcinosis, and renal failure. Nephrotic range proteinuria, normal calciuria, and hypokalemia have been rarely reported. It is unknown whether the changes in phenotype observed over time are explained by a decrease in glomerular filtration rate (GFR) or whether there is any phenotype-genotype relationship. To answer this we retrospectively analyzed data from 109 male patients with CLCN5 mutations (Dent-1) and 9 patients with mutation of the OCRL gene (Dent-2). In Dent-1 disease, the estimated GFR decreased with age, by 1.0 to 1.6 ml/min per 1.73 m(2)/yr in the absence and presence of nephrocalcinosis, respectively, with no significant difference. Median values of low-molecular-weight proteinuria were in the nephrotic range and remained at the same level even in late renal disease. End-stage renal disease occurred in 12 patients, at a median age of 40 years. Hypercalciuria decreased with glomerular filtration and was absent in 40% of the patients under 30 and 85% of those over the age of 30. Hypophosphatemia did not resolve with age and calcitriol concentrations were in the upper normal range. Kalemia decreased with age, with half of the patients over the age of 18 presenting with hypokalemia. Thus, no phenotype/genotype correlation was observed in this cohort of patients with Dent disease.

Mutations in OCRL encoding the inositol polyphosphate 5-phosphatase OCRL (Lowe oculocerebrorenal syndrome protein) disrupt phosphoinositide homeostasis along the endolysosomal pathway causing dysfunction of the cells lining the kidney proximal tubule (PT). The dysfunction can be isolated (Dent disease 2) or associated with congenital cataracts, central hypotonia and intellectual disability (Lowe syndrome). The mechanistic understanding of Dent disease 2/Lowe syndrome remains scarce due to limitations of animal models of OCRL deficiency. Here, we investigate the role of OCRL in Dent disease 2/Lowe syndrome by using OcrlY/− mice, where the lethal deletion of the paralogue Inpp5b was rescued by human INPP5B insertion, and primary culture of proximal tubule cells (mPTCs) derived from OcrlY/− kidneys. The OcrlY/− mice show muscular defects with dysfunctional locomotricity and present massive urinary losses of low-molecular-weight proteins and albumin, caused by selective impairment of receptor-mediated endocytosis in PT cells. The latter was due to accumulation of phosphatidylinositol 4,5–bisphosphate PI(4,5)P2 in endolysosomes, driving local hyper-polymerization of F-actin and impairing trafficking of the endocytic LRP2 receptor, as evidenced in OcrlY/− mPTCs. The OCRL deficiency was also associated with a disruption of the lysosomal dynamic and proteolytic activity. Partial convergence of disease-pathways and renal phenotypes observed in OcrlY/− and Clcn5Y/− mice suggest shared mechanisms in Dent diseases 1 and 2. These studies substantiate the first mouse model of Lowe syndrome and give insights into the role of OCRL in cellular trafficking of multiligand receptors. These insights open new avenues for therapeutic interventions in Lowe syndrome and Dent disease., Human Molecular Genetics, 28 (12), ISSN:0964-6906, ISSN:1460-2083

Dent disease 1 is a rare X-linked recessive inherited disease, caused by pathogenic variants in the chloride voltage-gated channel 5 (CLCN5) gene. Dent disease 1 is characterized by low molecular weight (LMW) proteinuria, hypercalciuria, nephrocalcinosis, and chronic kidney disease. Infants may manifest only asymptomatic LMW proteinuria, which increases the difficulty of early diagnosis. We describe two male infants presenting only with nephrotic-range LMW proteinuria observed on examination using urine protein electrophoresis. Hereditary renal tubular diseases were highly suspected based on early onset age and LMW proteinuria. Thus, next-generation sequencing (NGS) was performed and pathogenic mutations in CLCN5 were identified in both patients. A diagnosis of Dent disease 1 was established based on the above informations. The two patients developed hypercalciuria during late follow-up, which verified the diagnosis. These two cases highlight the importance of next-generation sequencing in the early diagnosis of Dent disease 1 with only LMW proteinuria.

Dent disease is an X-linked form of chronic kidney disease characterized by hypercalciuria, low molecular weight proteinuria, nephrocalcinosis, and proximal tubular dysfunction. Clinical presentation is highly variable. Male patients may present with early-onset rickets, recurrent nephrolithiasis, or insidiously with asymptomatic proteinuria or chronic kidney disease. Mutations in both the CLCN5 and OCRL1 genes have been associated with the Dent phenotype and are now classified as Dent-1 and Dent-2, respectively. This article describes the clinical presentation, laboratory evaluation, genetics, pathophysiology, management, and future therapies of Dent disease.

Phosphoinositides (PIs) play pivotal roles in the regulation of many biological processes. The quality and quantity of PIs is regulated in time and space by the activity of PI-kinases and PI-phosphatases. The number of PI metabolizing enzymes exceeds the number of PIs with, in many cases, more than one enzyme controlling the same biochemical step. This would suggest that the PI system has an intrinsic ability to buffer and compensate for the absence of a specific enzymatic activity. However, there are several examples of severe inherited human diseases caused by mutations in one of the PI-enzymes, although other enzymes with the same activity are fully functional. The kidney depends strictly on PIs for physiological processes such as cell polarization, filtration, solute reabsorption and extracellular signal transduction. Indeed, alteration of the PI system in the kidney very often results in pathological conditions, both inherited and acquired. Most of the knowledge of the roles that PIs play in the kidney comes from the study of knock-out animal models for genes encoding PI-enzymes and from the study of human genetic diseases such as Lowe syndrome/Dent disease 2 and Joubert syndrome caused by mutations in the genes encoding the PI-phosphatases OCRL and INPP5E, respectively.

Background Lowe syndrome (LS) is a rare genetic disorder caused by loss of function mutations in the X-linked gene, OCRL, which codes for inositol polyphosphate 5-phosphatase. LS is characterized by the triad of congenital cataracts, neurodevelopmental impairment (primarily intellectual and developmental disabilities [IDD]), and renal proximal tubular dysfunction. Studies carried out over the years have shown that hypomorphic mutations in OCRL adversely affect endosome recycling and actin polymerization in kidney cells and patient-derived fibroblasts. The renal problem has been traced to an impaired recycling of megalin, a multi-ligand receptor that plays a key role in the reuptake of lipoproteins, amino acids, vitamin-binding proteins, and hormones. However, the neurodevelopmental aspects of the disorder have been difficult to study because the mouse knockout (KO) model does not display LS-related phenotypes. Fortunately, the discovery of induced pluripotent stem (iPS) cells has provided an opportunity to grow patient-specific neurons, which can be used to model neurodevelopmental disorders in vitro, as demonstrated in the many studies that have been published in the past few years in autism spectrum disorders (ASD), schizophrenia (SZ), bipolar disorder (BD), and IDD. Methods We now report the first findings in neurons and neural progenitor cells (NPCs) generated from iPS cells derived from patients with LS and their typically developing male siblings, as well as an isogenic line in which the OCRL gene has been incapacitated by a null mutation generated using CRISPR-Cas9 gene editing. Results We show that neuronal cells derived from patient-specific iPS cells containing hypomorphic variants are deficient in their capacity to produce F-filamentous actin (F-actin) fibers. Abnormalities were also found in the expression of WAVE-1, a component of the WAVE regulatory complex (WRC) that regulates actin polymerization. Curiously, neuronal cells carrying the engineered OCRL null mutation, in which OCRL protein is not expressed, did not show similar defects in F-actin and WAVE-1 expression. This is similar to the apparent lack of a phenotype in the mouse Ocrl KO model, and suggests that in the complete absence of OCRL protein, as opposed to producing a dysfunctional protein, as seen with the hypomorphic variants, there is partial compensation for the F-actin/WAVE-1 regulating function of OCRL. Conclusions Alterations in F-actin polymerization and WRC have been found in a number of genetic subgroups of IDD and ASD. Thus, LS, a very rare genetic condition, is linked to a more expansive family of genes responsible for neurodevelopmental disorders that have shared pathogenic features. Electronic supplementary material The online version of this article (10.1186/s13229-018-0227-3) contains supplementary material, which is available to authorized users.

BACKGROUND: Dent disease type 1 (DD1) is a rare X-linked disorder caused mainly by CLCN5 mutations. Patients may present with nephrotic range proteinuria leading to erroneous diagnosis of focal segmental glomerulosclerosis (FSGS) and unnecessary immunosuppressive treatments. METHODS: The following cohorts were screened for CLCN5 mutations: Chronic Kidney Disease in Children (CKiD; n=112); Multicenter FSGS-Clinical Trial (FSGS-CT) (n=96) and Novel therapies for resistant FSGS Trial (FONT) (n=30). Urinary α(1)-microglobulin (α(1)-M), albumin (A), total protein (TP) and creatinine (Cr) were assessed from CKiD subjects (n=104); DD1 patients (n=14) and DD1 carriers (DC; n=8). TP/Cr, α1M/Cr, α1M/TP and A/TP from the CKiD cohort were compared with DD1 and DC. RESULTS: No CLCN5 mutations were detected. TP/Cr was lower in DC and CKiD with tubulointerstitial disease than DD1 and CKiD with glomerular disease (P < 0.002). α(1)M/Cr was higher in DD1 than CKiD and DC (P < 0.001). A/TP was lower in DD1, DC and CKiD with tubulointerstitial disease, higher in CKiD with glomerular disease (P < 0.001). Thresholds for A/TP of ≤ 0.21 and α(1)-M/Cr ≥ 120 mg/g (> 13.6 mg/mmol) creatinine were good screens for Dent disease. CONCLUSIONS: CLCN5 mutations were not seen in screened CKiD/FSGS cohorts. In our study, a cut off of TP/Cr > 600 mg/g (> 68 mg/mmol) and A/TP < 0.3 had a high sensitivity and specificity to distinguish DD1 from both CKiD glomerular and tubulointerstitial cohorts. α(1)-M/Cr ≥ 120 mg/g (> 13.6 mg/mmol) had the highest sensitivity and specificity when differentiating DD1 and studied CKiD populations.

Pseudo-Bartter/Gitelman syndrome (p-BS/GS) encompasses a clinically heterogeneous group of inherited or acquired disorders similar to Bartter syndrome (BS) or Gitelman syndrome (GS), both renal salt-losing tubulopathies. Phenotypic overlap frequently occurs between p-BS/GS and BS/GS, which are difficult to diagnose based on their clinical presentation and require genetic tests for accurate diagnosis. In addition, p-BS/GS can occur as a result of other inherited diseases such as cystic fibrosis, autosomal dominant hypocalcemia, Dent disease, or congenital chloride diarrhea (CCD). However, the detection of the variants in genes other than known BS/GS-causing genes by conventional Sanger sequencing requires substantial time and resources. We studied 27 cases clinically diagnosed with BS/GS, but with negative genetic tests for known BS/GS genes. We conducted targeted sequencing for 22 genes including genes responsible for tubulopathies and other inherited diseases manifesting with p-BS/GS symptoms. We detected the SLC26A3 gene variants responsible for CCD in two patients. In Patient 1, we found the SLC26A3 compound heterozygous variants: c.354delC and c.1008insT. In Patient 2, we identified the compound heterozygous variants: c.877G > A, p.(Glu293Lys), and c.1008insT. Our results suggest that a comprehensive genetic screening system using targeted sequencing is useful for the diagnosis of patients with p-BS/GS with alternative genetic origins.