OCRL Research Articles

Species-specific difference in expression and splice-site choice in Inpp5b, an inositol polyphosphate 5-phosphatase paralogous to the enzyme deficient in Lowe Syndrome

The oculocerebrorenal syndrome of Lowe (OCRL; MIM #309000) is an X-linked human disorder characterized by congenital cataracts, mental retardation, and renal proximal tubular dysfunction caused by loss-of-function mutations in the OCRL gene that encodes Ocrl, a type II phosphatidylinositol bisphosphate (PtdIns4,5P2) 5-phosphatase. In contrast, mice with complete loss-of-function of the highly homologous ortholog Ocrl have no detectable renal, ophthalmological, or central nervous system abnormalities. We inferred that the disparate phenotype between Ocrl-deficient humans and mice was likely due to differences in how the two species compensate for loss of the Ocrl enzyme. We therefore turned our attention to Inpp5b, another type II PtdIns4,5P2 5-phosphatase encoded by Inpp5b in mice and INPP5B in humans, as potential compensating genes in the two species, because Inpp5b/INPP5B are the most highly conserved paralogs to Ocrl/OCRL in the respective genomes of both species and Inpp5b demonstrates functional overlap with Ocrl in mice in vivo. We used in silico sequence analysis, reverse-transcription PCR, quantitative PCR, and transient transfection assays of promoter function to define splice-site usage and the function of an internal promoter in mouse Inpp5b versus human INPP5B. We found mouse Inpp5b and human INPP5B differ in their transcription, splicing, and primary amino acid sequence. These observations form the foundation for analyzing the functional basis for the difference in how Inpp5b and INPP5B compensate for loss of Ocrl function and, by providing insight into the cellular roles of Ocrl and Inpp5b, aid in the development of a model system in which to study Lowe syndrome.Electronic supplementary materialThe online version of this article (doi:10.1007/s00335-010-9281-7) contains supplementary material, which is available to authorized users.

X-inactivation analysis of embryonic lethality in Ocrl wt/−;Inpp5b −/− mice

Mutations in the human OCRL gene, which encodes a phosphatidylinositol(4,5)bisphosphate 5-phosphatase, result in the X-linked oculocerebrorenal syndrome of Lowe. Mice with a targeted disruption of Ocrl have no phenotypic abnormalities. Targeted disruption of its closest paralog, Inpp5b, causes male infertility in the 129S6 background. Mice with disruptions of both genes are lost in utero prior to 9.5-10.5 dpc, indicating that there is a functional overlap between the two paralogs early in development. We analyzed the pattern of X-inactivation in four tissues of distinct embryonic origin from Ocrl wt/−;Inpp5b −/− females to explore the timing and tissue distribution of the functional overlap. X-inactivation was strongly skewed against the disrupted Ocrl − allele being on the active X chromosome in all four tissues tested, indicating that there is early selection against cell lineages lacking both Ocrl and Inpp5b. Extraembryonic tissue was also involved in the lethality because there were never any live-born Ocrl wt/−;Inpp5b −/− females when the functional Ocrl wt allele was on the paternal X chromosome, which is preferentially inactivated in trophoblast-derived extraembryonic tissues. Live-born Ocrl wt/−;Inpp5b −/− females were found when the functional Ocrl wt allele was maternal, although in fewer numbers than expected. The importance of the extraembryonic tissues in the early embryonic lethality of embryos lacking both Ocrl and Inpp5b is reinforced by the successful isolation of a viable 40,XX Ocrl −/−;Inpp5b −/− embryonic stem cell from the inner cell mass of a 3.5-dpc blastocyst prior to implantation. These results indicate a functional overlap of Ocrl and Inpp5b in most cell lineages, especially in extraembryonic tissues.

Development of a multiplex ligation-dependent probe amplification (MLPA) assay for quantification of the OCRL1 gene

Objectives To develop and evaluate the efficacy of Multiplex Ligation-dependent Probe Amplification (MLPA) technique in detection of genomic rearrangements of the OCRL1 gene associated with Oculocerebrorenal syndrome of Lowe (OCRL). Design and methods Four synthetic MLPA probe sets have been designed to measure exons copy number in OCRL1 gene. After OCRL1 MLPA probe sets validation in 7 OCRL1 deleted patients, we screened 5 female patients to asses their carrier status and 15 patients with suspected OCRL, previously diagnosed as sequence-negative. Results MLPA was able to detect all the known deletions. Two of five females were detected as carrier for the family mutation. Neither mosaic deletion nor duplication was found in the 15 patients suspected of having Lowe syndrome. Conclusions Our MLPA allows rapid and precise OCRL1 gene quantification. Moreover this study provides no further evidence for the hypothesis that duplications and deletion somatic mosaic deletions account for the fraction of patients who have no detectible mutation after the usual screening procedures.

Dent's disease

Dent's disease is a renal tubular disorder characterized by manifestations of proximal tubule dysfunction, including low-molecular-weight proteinuria, hypercalciuria, nephrolithiasis, nephrocalcinosis, and progressive renal failure. These features are generally found in males only, and may be present in early childhood, whereas female carriers may show a milder phenotype. Prevalence is unknown; the disorder has been reported in around 250 families to date. Complications such as rickets or osteomalacia may occur. The disease is caused by mutations in either the CLCN5 (Dent disease 1) or OCRL1 (Dent disease 2) genes that are located on chromosome Xp11.22 and Xq25, respectively. CLCN5 encodes the electrogenic Cl-/H+ exchanger ClC-5, which belongs to the CLC family of Cl- channels/transporters. OCRL1 encodes a phosphatidylinositol bisphosphate (PIP2) 5-phosphatase and mutations are also associated with Lowe Syndrome. The phenotype of Dent's disease is explained by the predominant expression of ClC-5 in the proximal tubule segments of the kidney. No genotype-phenotype correlation has been described thus far, and there is considerable intra-familial variability in disease severity. A few patients with Dent's disease do not harbour mutations in CLCN5 and OCRL1, pointing to the involvement of other genes. Diagnosis is based on the presence of all three of the following criteria: low-molecular-weight proteinuria, hypercalciuria and at least one of the following: nephrocalcinosis, kidney stones, hematuria, hypophosphatemia or renal insufficiency. Molecular genetic testing confirms the diagnosis. The differential diagnosis includes other causes of generalized dysfunction of the proximal tubules (renal Fanconi syndrome), hereditary, acquired, or caused by exogenous substances. Antenatal diagnosis and pre-implantation genetic testing is not advised. The care of patients with Dent's disease is supportive, focusing on the treatment of hypercalciuria and the prevention of nephrolithiasis. The vital prognosis is good in the majority of patients. Progression to end-stage renal failure occurs between the 3rd and 5th decades of life in 30-80% of affected males.

Multiple Epidermal Cysts in Lowe Syndrome

Lowe syndrome is a rare genetic disease that appears to cause various clinical symptoms involving the eye, nervous system, and kidney. While a mutation of the OCRL1 gene is known to be responsible for this syndrome, the exact pathophysiology remains unclear. Various multi-organ symptoms are characteristic of Lowe syndrome, but skin lesions have rarely been described. Recently, mechanisms for the association of Lowe syndrome and skin lesions have been proposed. We report this case of Lowe syndrome involving multiple epidermal cysts on the scalp in a 6-year-old male child.

Locus heterogeneity of Dent’s disease: OCRL1 and TMEM27 genes in patients with no CLCN5 mutations

Dent's disease is an X-linked renal tubulopathy caused by mutations mainly affecting the CLCN5 gene. Defects in the OCRL1 gene, which is usually mutated in patients with Lowe syndrome, have recently been shown to lead to a Dent-like phenotype, called Dent's disease 2. About 25% of Dent's disease patients do not carry CLCN5/OCRL1 mutations. The CLCN4 and SLC9A6 genes have been investigated, but no mutations have been identified. The recent discovery of a novel mediator of renal amino acid transport, collectrin (the TMEM27 gene), may provide new insight on the pathogenesis of Dent's disease. We studied 31 patients showing a phenotype resembling Dent's disease but lacking any CLCN5 mutations by direct sequencing of the OCRL1 and TMEM27 genes. Five novel mutations, L88X, P161HfsX167, F270S, D506N and E720D, in the OCRL1 gene, which have not previously been reported in patients with Dent's or Lowe disease, were identified among 11 patients with the classical Dent's disease phenotype. No TMEM27 gene mutations were discovered among 26 patients, 20 of whom had an incomplete Dent's disease phenotype. Our findings confirm that OCRL1 is involved in the functional defects characteristic of Dent's disease and suggest that patients carrying missense mutations in exons where many Lowe mutations are mapped may represent a phenotypic variant of Lowe syndrome.

Inherited cerebrorenal syndromes

Abnormalities in the central nervous system and renal function are seen together in a variety of congenital syndromes. This Review examines the clinical presentation and the genetic basis of several such syndromes. The X-linked oculocerebrorenal syndrome of Lowe is characterized by developmental delay, blindness, renal tubular dysfunction, and progressive renal failure. This syndrome results from mutations in the OCRL gene, which encodes a phosphatase involved in endosomal trafficking. Mutations in OCRL also occur in Dent disease, which has a milder disease phenotype than Lowe syndrome. Patients with Joubert syndrome have cerebellar ataxia, pigmentary retinopathy, and nephronophthisis. Joubert syndrome is a genetically heterogeneous condition associated with mutations in at least five genes that encode ciliary proteins. Bardet-Biedl syndrome is a clinically variable condition associated with learning disabilities, progressive visual loss, obesity, polydactyly, hypogonadism, and cystic and fibrotic renal changes that can lead to renal failure. Most of the 12 genes mutated in Bardet-Biedl syndrome are also involved in ciliary function, as are the genes implicated in other 'ciliopathies' with similar phenotypes, including Meckel syndrome.

Amelioration of Hypophosphatemic Rickets and Osteoporosis With Pamidronate and Growth Hormone in Lowe Syndrome

The oculocerebrorenal syndrome of Lowe, an X-linked multisystem disorder, was diagnosed in a male patient who presented with typical abnormalities of the eyes, kidneys and nervous system. Besides congenital cataracts, renal tubular dysfunction and psychomotor retardation, the patient had also suffered from profound failure to thrive, growth hormone deficiency, severe osteoporosis with hypophosphatemic rickets, and progressive renal dysfunction since early childhood, which were attributed to the metabolic derangements following Fanconi syndrome. Direct sequencing of the OCRL1 gene (responsible for the oculocerebrorenal syndrome of Lowe) revealed a de novo c.2282_2283insT in exon 20, which resulted in premature termination of translation (D762X). After monthly intravenous administration of pamidronate since the age of 17.8 years, his urine creatinine clearance and tubular resorption of phosphate increased slightly and bone mineral density was much improved (Z score increased from -7.3 to -3.3) without deterioration of renal function. Simultaneous growth hormone therapy enhanced the positive response. The beneficial osseous and renal effects of the bisphosphonate, along with growth hormone treatment in Lowe syndrome with hypophosphatemia, may be related to reduced renal calcium and phosphate excretion.

A PH domain within OCRL bridges clathrin-mediated membrane trafficking to phosphoinositide metabolism

OCRL, whose mutations are responsible for Lowe syndrome and Dent disease, and INPP5B are two similar proteins comprising a central inositol 5-phosphatase domain followed by an ASH and a RhoGAP-like domain. Their divergent NH2-terminal portions remain uncharacterized. We show that the NH2-terminal region of OCRL, but not of INPP5B, binds clathrin heavy chain. OCRL, which in contrast to INPP5B visits late stage endocytic clathrin-coated pits, was earlier shown to contain another binding site for clathrin in its COOH-terminal region. NMR structure determination further reveals that despite their primary sequence dissimilarity, the NH2-terminal portions of both OCRL and INPP5B contain a PH domain. The novel clathrin-binding site in OCRL maps to an unusual clathrin-box motif located in a loop of the PH domain, whose mutations reduce recruitment efficiency of OCRL to coated pits. These findings suggest an evolutionary pressure for a specialized function of OCRL in bridging phosphoinositide metabolism to clathrin-dependent membrane trafficking.

Truncating Mutations in the Chloride/Proton ClC-5 Antiporter Gene in Seven Jewish Israeli Families with Dent’s 1 Disease

Dent’s disease is an X-linked hereditary renal tubular disorder characterized by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets and progressive renal failure. About 60% of patients have mutations in the CLCN5 gene (Dent 1), which encodes a kidney-specific chloride/proton antiporter, and 15% of patients have mutations in the OCRL1 gene (Dent 2). The aim of the study was to identify CLCN5 mutations in Jewish Israeli families with Dent‘s disease and to characterize the associated clinical syndromes. We studied 17 patients from 14 unrelated Israeli families with a clinical diagnosis of Dent’s disease. LMWP was detected in all patients. Most of the affected individuals had hypercalciuria and nephrocalcinosis. Renal stones were found in 1 patient, and renal insufficiency developed in 2 patients. We identified six different truncating CLCN5 mutations that were segregated with the disease in 7 families: three nonsense mutations (Arg28stop, Arg467stop and Arg637stop), one deletion mutation (505delA) and two novel mutations, consisted of one deletion mutation (1493delG) and one insertion mutation (409insC). All the mutations cause premature termination of protein translation and result in a non-functional truncated protein. The clinical characteristics of patients with different mutations were, in general, similar.

A case of Lowe syndrome (oculocerebrorenal syndrome): Clinical implications and anaesthetic management

Cataract surgery in neonates and infants can be quite challenging, as many of these children may be having congenital anomalies like Downs, infections like rubella etc. LOWE syndrome is one of the few conditions where the child is born with cataract. LOWE syndrome is a rare X- linked disorder characterised by congenital cataract, mental retardation and Fanconies syndrome. The disease is caused by the mutations of OCRL gene which encodes phospatydyl inositol (4, 5) biphosphatase (Ptdlns (4, 5) P2 phosphatase), protein. We report here the perioperative management of a child with LOWE syndrome who was operated for congenital cataract.

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

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. 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. 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. 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.

Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, and Facial Dysmorphism in a Case of Lowe Syndrome with Novel OCRL1 Gene Mutation

Lowe syndrome is a multisystem disorder characterized by anomalies of the eye, the nervous system, and the kidney. It is an uncommon, X-linked disease. Bilateral cataract and severe hypotonia are present at birth. Psychomotor retardation is evident in childhood, while renal complications arise in adolescence. The mutation of the gene OCRL1 localized at Xq26.1 is responsible for the disease. The authors report on a 12-year-old male with mental retardation, facial dysmorphism as prominent forehead, long and slender-shaped face, prominent eyebrows, epicanthus, microphthalmia, low-posterior set ears with prominent helix and antihelix, long philtrum, and mild prognathia. He also had history of neonatal hypotonia and congenital cataracts. His cranial magnetic resonance imaging showed increased signal intensity in white matter on T2-weighted images, and magnetic resonance spectroscopy revealed elevation of the myoinositol peak at 3.56 ppm. Molecular analysis of OCRL1 gene revealed novel N574K mutation on 17th exon.

Mutations in OCRL1 gene in Indian children with Lowe syndrome

Lowe syndrome is an X-linked disorder secondary to mutations involving the OCRL1 gene. There are no data on the spectrum of the disease in the Asian population. Detailed clinical assessment, a laboratory assessment which included both glomerular and tubular function tests and genomic DNA analysis, was carried out in six unrelated patients with Lowe syndrome. Analysis of this gene in six unrelated patients with Lowe syndrome showed novel mutations in four and previously described mutations in two. These included a missense mutation (exon 10), two nonsense mutations (exons 10 and 21), two frameshift mutations (exons 12 and 21) and a mutation at the acceptor site of intron 22. The mothers were found to be heterozygote carriers in four cases. This is the first report of mutations involving the OCRL1 gene in patients with Lowe syndrome of Indian origin. These observations have implications for genetic counseling and prenatal diagnosis for families with Lowe syndrome.

Novel OCRL1 Mutations in Patients With the Phenotype of Dent Disease

Dent disease is an X-linked tubulopathy frequently caused by mutations affecting the voltage-gated chloride channel and chloride/proton antiporter ClC-5. A recent study showed that defects in OCRL1, encoding a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ocrl) and usually found mutated in patients with Lowe syndrome, also can provoke a Dent-like phenotype (Dent 2 disease). We investigated 20 CLCN5-negative males from 17 families with a phenotype resembling Dent disease for defects in OCRL1. In our complete series of 35 families with a phenotype of Dent disease, a mutation in the OCRL1 gene was detected in 6 kindreds. All were novel frameshift (Q70RfsX88 and T121NfsX122, detected twice) or missense mutations (I257T and R476W). None of our patients had cognitive or behavioral impairment or cataracts, 2 classic hallmarks of Lowe syndrome. All patients had mild increases in lactate dehydrogenase and/or creatine kinase levels, which rarely is observed in CLCN5-positive patients, but frequently found in patients with Lowe syndrome. To explain the phenotypic heterogeneity caused by OCRL1 mutations, we performed extensive data-bank mining and extended reverse-transcriptase polymerase chain reaction analysis, which provided no evidence for yet unknown (tissue-specific) alternative OCRL1 transcripts. Mutations in the OCRL1 gene are found in approximately 23% of kindreds with a Dent phenotype. Defective protein sorting/targeting of Ocrl might be the reason for mildly elevated creatine kinase and lactate dehydrogenase serum concentrations in these patients and a clue to suspect Dent disease unrelated to CLCN5 mutations. It remains to be elucidated why the various OCRL1 mutations found in patients with Dent 2 disease do not cause cataracts.

A novel interstitial deletion in Xq25, identified by array-CGH in a patient with Lowe syndrome

The oculocerebrorenal syndrome of Lowe (OCRL) (MIM:309000) is an X-linked multisystemic disorder affecting the eyes, nervous system and kidneys due to mutations in OCRL1 gene. The gene contains 24 exons, and encodes a 105 kDa phosphatydylinositol 4,5-biphosphate [PtdIns(4,5)P 2] 5-phosphatase localized primarily in the trans-Golgi network and the lysosomes. The large majority of the OCRL1 mutations producing Lowe syndrome are either missense mutations localized mainly in the catalytic domain or non-sense/frameshift mutations resulting in truncated proteins. Rarely, in about 6% of the cases, the disease results from large gene deletions occurring in the 5′ part of the gene. Here we report a new case of a patient with Lowe syndrome due to a deletion of about 4 Mb, encompassing the OCRL1 gene, detected by PCR and CGH array. The mother was carrier of the same deletion.

The effect of missense mutations in the RhoGAP-homology domain on ocrl1 function

Lowe syndrome is a rare X-linked disease characterized by congenital cataracts, defects in renal tubule cell function, and mental retardation. Mutations in the OCRL1 gene, which encodes ocrl1, a phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P 2) 5-phosphatase, are the cause of Lowe syndrome. PtdIns(4,5)P 2, a substrate of ocrl1, is an important signaling molecule within the cell. OCRL1 is ubiquitously expressed and co-localizes with the trans-Golgi network (TGN) and endosomal proteins. The ocrl1 protein contains two recognizable domains, one a conserved Ptd(4,5)P 2 5-phosphatase domain and the other with homology to Rho GTPase activating proteins (RhoGAPs). The objective of our study was to further characterize the ocrl1 RhoGAP-homology domain by analyzing the effect of two missense mutations in this domain, I751N and A780P, which were previously reported in Lowe syndrome patients. Both mutant proteins were expressed at levels similar to wild-type but their enzyme activity was reduced by 85–90%, indicating that the RhoGAP-homology domain is important for the enzymatic function of ocrl1. Study of a C-terminal region of wild-type ocrl1 containing this domain detected no GAP activity, eliminating the possibility of an effect by mutations in this domain on GTPase activation. Because members of the Arf family of small G-proteins are directly involved in (Ptd(4,5)P 2) signaling and localize to the TGN like ocrl1, we analyzed by immunoprecipitation the interaction of ocrl1 with Arf1 and Arf6 via its RhoGAP-homology domain. Wild-type ocrl1, but not the I751N mutant protein, co-immunoprecipitated with these two Arf proteins. These results indicate that wild-type ocrl1 and Arf proteins can interact and that this interaction is disrupted by the mutation. It remains unknown whether a disrupted interaction between Arf and ocrl1 plays a role in the Lowe syndrome phenotype.

Self-assessment

A male infant was delivered, after an uneventful pregnancy, at term with no associated perinatal complications. At routine baby check the infant was noted to be hypotonic, had cryptorchidism and had the abnormality seen in Fig. 1 (present bilaterally). Examination was otherwise normal and paediatric follow-up during infancy revealed growth and development parameters to be within normal limits (accounting for visual difficulties). During the second year, however, weight and length began falling across centile lines on the growth chart despite close attention to nutrition. Generalised developmental delay also became apparent toward the end of the second year. Measurement of urinary amino acids at birth was essentially normal, but, at 20 months of age a generalised aminoaciduria, phosphaturia, calciuria and proteinuria was demonstrated, with urine pH being 6.5. 1.What is the abnormality seen in Fig. 1?(a)Cystine crystals(b)Retinoblastoma(c)Lenticular coloboma(d)Cataract(e)Retinal detachment2.What is the likely diagnosis?(a)Cystinosis(b)Down's syndrome(c)Oculo-cerebro-renal syndrome (Lowe's syndrome)(d)Cystinuria(e)Congenital rubella3.Which test in infancy would have been most helpful in establishing a diagnosis?(a)Renal biopsy(b)Corneal biopsy(c)Karyotype(d)Screening for congenital infection(e)OCRL1 gene mutation analysis

Identification of OCRL1 Mutations in Two Taiwanese Lowe Syndrome Patients

The oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked multisystem disorder characterized by congenital cataracts, mental retardation, and renal tubular dysfunction. The OCRL1 gene responsible for Lowe syndrome has been mapped to chromosome Xq24-q26. We analyzed two Taiwanese OCRL patients and their families. In Case 1, a splicing mutation (889-11 G --> A) was identified in intron 10 of the OCRL1 gene. The mother is a heterozygous carrier. The 889-11 G --> A mutation results in an abnormal splicing and predicts premature termination of translation. In Case 2, a novel de novo missense mutation (1373G --> A, P458H) was identified in exon 14 of the OCRL1 gene. The missense mutation predicts a substitution in a domain highly conserved among the inositol-5-phosphatase family.

Dent's disease

Dent's disease is a renal tubular disorder characterized by manifestations of proximal tubule dysfunction, including low-molecular-weight proteinuria, hypercalciuria, nephrolithiasis, nephrocalcinosis, and progressive renal failure. These features are generally found in males only, and may be present in early childhood, whereas female carriers may show a milder phenotype. Prevalence is unknown; the disorder has been reported in around 250 families to date. Complications such as rickets or osteomalacia may occur. The disease is caused by mutations in either the CLCN5 (Dent disease 1) or OCRL1 (Dent disease 2) genes that are located on chromosome Xp11.22 and Xq25, respectively. CLCN5 encodes the electrogenic Cl-/H+ exchanger ClC-5, which belongs to the CLC family of Cl- channels/transporters. OCRL1 encodes a phosphatidylinositol bisphosphate (PIP2) 5-phosphatase and mutations are also associated with Lowe Syndrome. The phenotype of Dent's disease is explained by the predominant expression of ClC-5 in the proximal tubule segments of the kidney. No genotype-phenotype correlation has been described thus far, and there is considerable intra-familial variability in disease severity. A few patients with Dent's disease do not harbour mutations in CLCN5 and OCRL1, pointing to the involvement of other genes. Diagnosis is based on the presence of all three of the following criteria: low-molecular-weight proteinuria, hypercalciuria and at least one of the following: nephrocalcinosis, kidney stones, hematuria, hypophosphatemia or renal insufficiency. Molecular genetic testing confirms the diagnosis. The differential diagnosis includes other causes of generalized dysfunction of the proximal tubules (renal Fanconi syndrome), hereditary, acquired, or caused by exogenous substances. Antenatal diagnosis and pre-implantation genetic testing is not advised. The care of patients with Dent's disease is supportive, focusing on the treatment of hypercalciuria and the prevention of nephrolithiasis. The vital prognosis is good in the majority of patients. Progression to end-stage renal failure occurs between the 3rd and 5th decades of life in 30-80% of affected males.