X-linked Recessive Nephrolithiasis Research Articles

Recent advances in understanding the clinical and genetic heterogeneity of Dent's disease

Dent’s disease 1 (OMIM 300009) is an X-linkedproximal tubulopathy [1] first described in 1964 [2],with Fanconi syndrome, a consistent renal abnor-mality, and low-molecular-weight proteinuria (LMWP)being almost always present. Nephrocalcinosisand renal stone formation occur more frequentlyin Dent’s disease 1 than in other forms of Fanconisyndrome.Various features of Dent’s disease 1 predominatein different ethnic groups, and have been noted inearlier reports, resulting in several syndrome names ofphenotypically similar disorders. These were referredto as X-linked recessive hypophosphataemic rickets(XLRH), X-linked recessive nephrolithiasis (XRN)and familial idiopathic LMWP in Japanese patients(JILMWP), often referred to as Dent’s Japan disease[3,4]. All of these are now considered phenotypicvariants of one unique entity, namely Dent’s disease 1[5,6].

Identification of a novel splice site mutation of CLCN5 gene and characterization of a new alternative 5' UTR end of ClC-5 mRNA in human renal tissue and leukocytes.

Mutations in the CLCN5 gene have been detected in Dent's disease and its phenotypic variants (X-linked recessive nephrolithiasis, X-linked recessive hypophosphatemic rickets, and idiopathic low-molecular-weight proteinuria of Japanese children). Dent's disease is a tubular disorder characterized by low-molecular-weight proteinuria, and nephrolithiasis associated with nephrocalcinosis and hypercalciuria. ClC-5 is the first chloride channel for which a definitive role in the trafficking and acidification-dependent recycling of apical membrane proteins has been established. In the course of CLCN5 SSCP analysis in patients with hypercalciuric nephrolithiasis, we detected a novel mutation at intron 2 of the CLCN5 gene, a T-to-G substitution, located 17 bp upstream of the AG acceptor site. To determine the effect of IVS2-17 T>G mutation on the correct splicing of intron 2, we studied ClC-5 transcripts in a patient's peripheral blood leukocytes by means of quantitative comparative RT/PCR, and found a new ClC-5 5' UTR isoform characterized by the untranslated exon 1b and by retention of intron 1b. This new isoform--isoform B1--was not correlated with mutation since it was detected also in control leukocytes and in renal tissues of kidney donors, thus confirming its physiological role. By RACE analysis we determined the putative transcriptional start site which is located at intron 1a, 251 nt upstream of the first nucleotide of the untranslated exon 1b. ORF analysis revealed that intron 1b retention in isoform B1 stabilizes the initiation of translation to the AGT at position 297 of the ClC-5 cDNA coding region.

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

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

Voltage-gated ion channels and hereditary disease.

By the introduction of technological advancement in methods of structural analysis, electronics, and recombinant DNA techniques, research in physiology has become molecular. Additionally, focus of interest has been moving away from classical physiology to become increasingly centered on mechanisms of disease. A wonderful example for this development, as evident by this review, is the field of ion channel research which would not be nearly as advanced had it not been for human diseases to clarify. It is for this reason that structure-function relationships and ion channel electrophysiology cannot be separated from the genetic and clinical description of ion channelopathies. Unique among reviews of this topic is that all known human hereditary diseases of voltage-gated ion channels are described covering various fields of medicine such as neurology (nocturnal frontal lobe epilepsy, benign neonatal convulsions, episodic ataxia, hemiplegic migraine, deafness, stationary night blindness), nephrology (X-linked recessive nephrolithiasis, Bartter), myology (hypokalemic and hyperkalemic periodic paralysis, myotonia congenita, paramyotonia, malignant hyperthermia), cardiology (LQT syndrome), and interesting parallels in mechanisms of disease emphasized. Likewise, all types of voltage-gated ion channels for cations (sodium, calcium, and potassium channels) and anions (chloride channels) are described together with all knowledge about pharmacology, structure, expression, isoforms, and encoding genes.

Chloride channel CLCN5 mutations in Japanese children with familial idiopathic low molecular weight proteinuria

Familial idiopathic low molecular weight proteinuria (FILMWP) is a renal proximal tubulopathy characterized by mild proteinuria consisting of low molecular weight proteinuria and relatively conserved renal function in young patients, but without rickets. Mutations in the renal chloride channel CLCN5 gene have been reported in three disorders of hypercalciuric nephrolithiasis and in FILMWP. To assess the relationship between molecular defects and phenotypic variations, we analyzed the CLCN5 gene from three additional Japanese families with FILMWP using single-strand conformation polymorphism and sequencing. We identified three mutations: a single base insertion at codon 514; a single base deletion at codon 116; and a nonsense mutation, R704X. The R704X mutation is identical to that found in X-linked recessive nephrolithiasis, but there was no renal failure in our patient. The first two mutations caused a shift in the reading frame, and all introduced a premature stop codon, resulting in synthesis of truncated CLC-5 proteins that lacked 220 (29%), 610 (82%), and 43 (6%) amino acids, respectively. These mutations were demonstrated to cosegregate with the disease in each of the three families. We conclude that the CLCN5 gene is responsible for the renal proximal tubulopathy in many Japanese families and suggest that molecular defects, environmental factors, or other modifying genes may account for the different phenotypes.

X-linked recessive nephrolithiasis: Presentation and diagnosis in children

We report a new X-linked recessive nephrolithiasis kindred. X-linked recessive nephrolithiasis is a recently described disease characterized by recurrent nephrolithiasis, nephrocalcinosis, and progressive renal failure, associated with mutations in a renal chloride channel gene, chloride channel number 5. Screening individuals at risk with renal ultrasonography and measurement of urinary excretion of low molecular weight proteins and calcium will exclude boys without X-linked recessive nephrolithiasis kindred and identify boys likely to have the disease. (J Pediatr 1998:132:859-62)

Mutations in CLCN5 chloride channel in Japanese patients with low molecular weight proteinuria.

Mutations in the CLCN5 gene have been demonstrated in three disorders of hypercalciuric nephrolithiasis, i.e., Dent's disease, X-linked recessive nephrolithiasis, and X-linked recessive hypophosphatemic rickets. Recently, a number of Japanese children with low molecular weight proteinuria (LMWP) showing symptoms similar to those shown by patients with Dent's disease in British families have also been reported to have mutations in the CLCN5 gene. The present study examines five unrelated Japanese families with LMWP, two of which lacked any signs other than LMWP, and three of which had several signs other than LMWP, i.e., hypercalciuria, aminoaciduria, hypophosphatemia, and rickets. One nonsense (E118X) and one missense (W22G) mutation were found in three patients in the two families having only LMWP. One genomic deletion including exons 5 to 8 in the CLCN5 gene was found in a patient with hypophosphatemic rickets, and a nonsense mutation (R347X) was found in one patient with LMWP and slight hypercalciuria. No mutations of the exons and exon-intron boundaries in the CLCN5 gene were found in one patient with LMWP, aminoaciduria, and hypokalemia. In addition to the predicted loss of chloride channel function in these nonsense and deletion mutations, the loss of function in the missense mutation W22G was confirmed in the Xenopus oocyte expression system. These results clarified four novel mutations in the CLCN5 genes, and additionally suggested that the loss-of-function mutation of the CLCN5 does not necessarily lead to hypercalciuria and nephrocalcinosis in the early stage of the disease, and that LMWP is an early and essential manifestation of disorders of the CLC-5 chloride channel.

X-linked hypercalciuric nephrolithiasis: Clinical syndromes and chloride channel mutations

The recent discovery of a gene responsible for a particular form of hypercalciuric nephrolithiasis has created excitement because it promises to shed light on mechanisms involved in both calcium stone formation and renal epithelial function. The disease that I will refer to here as X-linked hypercalciuric nephrolithiasis (XLHN) has been the subject of some confusion owing to the fact that it has been described over the past five years by different groups using different names, all but one of them polysyllabic: “X-linked recessive nephrolithiasis with renal failure” in North America, “Dent’s disease” in the United Kingdom, “X-linked recessive hypophosphatemic rickets” in Italy, and “low-molecularweight proteinuria with hypercalciuria and nephrocalcinosis” in Japan. These syndromes differ in degree from each other, but common themes include proximal tubular reabsorptive failure, nephrolithiasis, nephrocalcinosis, progressive renal insufficiency, and in some cases rickets. The fact of mutations in the same gene in each of these syndromes has now established that they are phenotypic variants of a single disease and not separate entities. Clinical studies of these patients produced few clues as to the pathophysiology of the condition, and the gene responsible for this disease was identified through a positional cloning approach rather than through the study of logical candidate genes. The gene identified, CLCN5, was novel. Sequence homology suggested, and expression studies confirmed, that the gene product was a member of the CLC family of voltage-gated chloride channels. This was a surprise, since it is not immediately clear how mutations in such a chloride channel could explain the clinical findings in this disease. The physiology of the gene product, designated CLC-5, is at present only partly understood, and is the subject of active research. SYNDROMES OF X-LINKED HYPERCALCIURIC NEPHROLITHIASIS Four syndromes of X-linked hypercalciuric nephrolithiasis (XLHN) were reported independently, but mutations in the chloride channel gene CLCN5 have been identified in all four syndromes, justifying the view that these together represent a single disease. Table 1 summarizes the features of these syndromes as originally described. An understanding of these reports is valuable in that it emphasizes the range of phenotypes in this disease, and as an effort to clarify the relationships among what some might otherwise be tempted to consider as separate entities.

A common molecular basis for three inherited kidney stone diseases.

Kidney stones (nephrolithiasis), which affect 12% of males and 5% of females in the western world, are familial in 45% of patients and are most commonly associated with hypercalciuria. Three disorders of hypercalciuric nephrolithiasis (Dent's disease, X-linked recessive nephrolithiasis (XRN), and X-linked recessive hypophosphataemic rickets (XLRH)) have been mapped to Xp11.22 (refs 5-7). A microdeletion in one Dent's disease kindred allowed the identification of a candidate gene, CLCN5 (refs 8,9) which encodes a putative renal chloride channel. Here we report the investigation of 11 kindreds with these renal tubular disorders for CLCN5 abnormalities; this identified three nonsense, four missense and two donor splice site mutations, together with one intragenic deletion and one microdeletion encompassing the entire gene. Heterologous expression of wild-type CLCN5 in Xenopus oocytes yielded outwardly rectifying chloride currents, which were either abolished or markedly reduced by the mutations. The common aetiology for Dent's disease, XRN and XLRH indicates that CLCN5 may be involved in other renal tubular disorders associated with kidney stones.

Characterization of carrier females and affected males with X-linked recessive nephrolithiasis

X-linked recessive nephrolithiasis (XRN) was described in a large kindred in which nephrolithiasis; proximal tubular dysfunction, proteinuria, nephrocalcinosis, and renal failure occur only in males. Carrier females are asymptomatic, but formal studies of them have not been done. The gene for XRN has been mapped to the pericentromeric region of the X chromosome, close to the loci for several eye disease genes. We studied six affected males, 13 carrier females, and 25 normal members of this family including 7 females whose genetic haplotype predicted them to be carriers. Studies were done in the Clinical Research Unit on a diet containing 400 mg of calcium and 2 g of sodium, and by an additional outpatient urine collection was obtained on a 1-g calcium intake. Hypercalciuria occurred in five of six affected males, 4 of 12 carrier females, and three of seven predicted carriers. Significant proteinuria was present in all affected males and in no other subjects. Low-molecular-weight proteinuria was present in all affected males: the excretion of alpha 1-microglobulin exceeded normal by 3- to 14-fold, of beta 2-microglobulin exceeded normal by 100- to 400-fold, and of retinol-binding protein exceeded normal by 1,000- to 3,000-fold. The excretion of these proteins was less strikingly elevated in carrier females, but the excretion of alpha 1-microglobulin was abnormal in 9 of 15 carriers, beta 2-microglobulin was abnormal in 12 of 15, and retinolbinding protein in was abnormal 12 of 13, and this pattern was similar in predicted carriers. The urinary concentrating ability was abnormal in four affected males with renal insufficiency but normal in all other subjects. Urinary wasting of potassium, phosphorous, and glucose occurred infrequently, and no subject was hypouricemic. Formal ophthalmologic studies were normal in five affected males. Thus, the most consistent urinary abnormalities in XRN are hypercalciuria and low-molecular-weight proteinuria, the latter of which appears to be a marker for the carrier state.

Characterization of carrier females and affected males with X-linked recessive nephrolithiasis.

X-linked recessive nephrolithiasis (XRN) was described in a large kindred in which nephrolithiasis; proximal tubular dysfunction, proteinuria, nephrocalcinosis, and renal failure occur only in males. Carrier females are asymptomatic, but formal studies of them have not been done. The gene for XRN has been mapped to the pericentromeric region of the X chromosome, close to the loci for several eye disease genes. We studied six affected males, 13 carrier females, and 25 normal members of this family including 7 females whose genetic haplotype predicted them to be carriers. Studies were done in the Clinical Research Unit on a diet containing 400 mg of calcium and 2 g of sodium, and by an additional outpatient urine collection was obtained on a 1-g calcium intake. Hypercalciuria occurred in five of six affected males, 4 of 12 carrier females, and three of seven predicted carriers. Significant proteinuria was present in all affected males and in no other subjects. Low-molecular-weight proteinuria was present in all affected males: the excretion of alpha 1-microglobulin exceeded normal by 3- to 14-fold, of beta 2-microglobulin exceeded normal by 100- to 400-fold, and of retinol-binding protein exceeded normal by 1,000- to 3,000-fold. The excretion of these proteins was less strikingly elevated in carrier females, but the excretion of alpha 1-microglobulin was abnormal in 9 of 15 carriers, beta 2-microglobulin was abnormal in 12 of 15, and retinolbinding protein in was abnormal 12 of 13, and this pattern was similar in predicted carriers. The urinary concentrating ability was abnormal in four affected males with renal insufficiency but normal in all other subjects. Urinary wasting of potassium, phosphorous, and glucose occurred infrequently, and no subject was hypouricemic. Formal ophthalmologic studies were normal in five affected males. Thus, the most consistent urinary abnormalities in XRN are hypercalciuria and low-molecular-weight proteinuria, the latter of which appears to be a marker for the carrier state.

Mapping the gene causing X-linked recessive nephrolithiasis to Xp11.22 by linkage studies.

X-linked recessive nephrolithiasis is associated with kidney stones and renal tubular dysfunction in childhood progressing to renal failure in adulthood. The primary defect causing this renal tubular disorder is unknown and determining the chromosomal location of the mutant gene would represent an important step toward defining the biochemical basis. We have performed linkage studies in 102 members (10 affected males, 47 unaffected males, 15 obligate heterozygote females, and 30 unaffected females) from five generations of one family. As genetic markers we used 10 cloned human X chromosome fragments identifying restriction fragment length polymorphisms and seven pairs of oligonucleotide primers identifying microsatellite polymorphisms. Linkage with the locus DXS255 was established with a peak LOD score = 5.91 at 3.6% recombination, thereby localizing the X-linked recessive nephrolithiasis gene to the pericentromeric region of the short arm of the X chromosome (Xp11.22). Multilocus analysis indicated that the mutant gene was distal to DXS255 but proximal to the Duchenne muscular dystrophy locus on Xp. Thus, the gene that causes X-linked recessive nephrolithiasis maps to the pericentromeric region of the short arm of the X chromosome (Xp11.22), and further characterization of this gene will help to elucidate the factors controlling renal tubular function and mineral homeostasis.

X-Linked Recessive Nephrolithiasis with Renal Failure

Nephrolithiasis may occur as a consequence of a number of hereditary disorders. We describe a large kindred from northern New York with hereditary nephrolithiasis accompanied by urinary concentrating defects, nephrocalcinosis, renal insufficiency, and renal wasting of potassium, phosphate, calcium, and uric acid. The pattern of inheritance was established by examining the patients and their records and interviewing family members. Selected members of the family were evaluated in detail, with measurements of erythrocyte cation fluxes and carbonic anhydrase (carbonate dehydratase) activity. The kindred consisted of 162 family members from six generations. All nine affected persons were male and appeared to have inherited the disease from their mothers. No affected man transmitted the gene to a son, but the daughters of affected men were carriers. The patients presented in childhood with calcium nephrolithiasis and proteinuria, with progression to nephrocalcinosis, urinary concentrating defects, and renal insufficiency. Renal biopsies revealed tubular atrophy, interstitial fibrosis, and glomerulosclerosis; the characteristic features of other forms of hereditary nephritis were absent. Abnormalities in the renal excretion of calcium, phosphate, potassium, and uric acid were found only in the adult members of the kindred, although renal biopsies were abnormal even in younger members. In one patient who has had a renal transplant for seven years, the disease has not recurred. This kindred manifested an X-linked recessive nephrolithiasis with renal failure, a new form of hereditary renal disease. Most of the identifiable physiologic abnormalities occurred after the development of nephrolithiasis and renal insufficiency and may not be of pathogenetic importance.