Isolated hypercalciuria with mutation in CLCN5: relevance to idiopathic hypercalciuria

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

儿童特发性高钙尿症52例临床分析

目的探讨特发性高钙尿症（IH）的临床特点及与泌尿系结石的关系。方法分析52例确诊为IH患儿的临床资料特点,并结合文献讨论其与泌尿系结石发生的关系。结果52例患儿均有不同程度血尿。其中41例患儿行腹部B超和X线平片检查及静脉肾盂造影检查,发现肾结石5例。调查52例患儿家族史发现15例家族中有泌尿系结石患者,6例同胞中有类似血尿患者,较正常对照组家族的尿结石发病率明显增高（P〈0．05）。52例患儿进行钙负荷试验,其中肠道吸收亢进型29例．肾脏漏出型23例。结论除血尿外,泌尿系结石也是IH的常见临床表现,尤其见于高钙尿状态持续时间较长者。IH与家族泌尿系结石的发病有密切关系,有遗传倾向。     

New insights into the pathogenesis of idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) is the most common metabolic abnormality in patients with calcium kidney stones. It is characterized by normocalcemia, absence of diseases that cause increased urine calcium, and calcium excretion that is greater than 250 mg/d in women and 300 mg/d in men. Subjects with IH have a generalized increase in calcium turnover, which includes increased gut calcium absorption, decreased renal calcium reabsorption, and a tendency to lose calcium from bone. Despite the increase in intestinal calcium absorption, a negative calcium balance is seen commonly in balance studies, especially on a low-calcium diet. The mediator of decreased renal calcium reabsorption is not clear; it is not associated with either an increase in filtered load of calcium or altered parathyroid hormone levels. There is an increased incidence of hypercalciuria in first-degree relatives of those with IH, but IH appears to be a complex polygenic trait with a large contribution from diet to expression of increased calcium excretion. Increased tissue vitamin D response may be responsible for the manifestations of IH in at least some patients.     

Clinical presentation and metabolic features of overt and occult urolithiasis

Although pediatricians are frequently confronted with patients presenting urolithiasis symptoms without obvious stones, the syndrome of occult urolithiasis may be still viewed with some skepticism. We have compared the clinical and metabolic features of 197 children with obvious calculi, 189 with microcalculi (diameter ≤3 mm based on renal sonography), and 114 with symptoms of urolithiasis and normal renal sonography findings. Only microcalculi and normal sonography subjects with a urinary abnormality potentially leading to urolithiasis were included in the study. Age at presentation increased significantly (p = 0.0001) in the groups in the order normal sonography to microcalculi to calculi groups. There was no significant difference among the three groups in terms of family history of urolithiasis, gender distribution, and degree of hypercalciuria, hyperuricosuria, hyperoxaluria, or hypocitraturia. The average frequency of pain attacks of patients with recurrent abdominal pain (RAP) ranged from 3.6 to 4.6 days of pain per month among the three groups, which is four to ninefold lower than that reported for children with functional or organic gastrointestinal RAP. The consistency of many clinical and urinary metabolic characteristics indicates a common underlying disorder in overt and occult urolithiasis. The increase of age at presentation from the normal sonography to microcalculi and calculi groups may reflect progressive crystal accretion leading ultimately to overt stone formation.     

Metabolic disturbance as a cause of recurrent hematuria in children

Metabolic disturbance as a cause of recurrent hematuria in children. To evaluate metabolic disturbance as a cause of hematuria, 250 children, aged eight months to fourteen years, with recurrent hematuria were studied. In the present series, metabolic disturbance was mainly due to idiopathic hypercalciuria (IH), the most common etiology of hematuria without proteinuria in childhood. Sixty-seven (27%) of the children had IH, ten children (4%) had hyperuricosuria, and 27 (11%) had nephrolithiasis. To better characterize the IH into renal (RH) or absorptive hypercalciuria (AH) subtypes, 45 of the 67 children (ranging age from six to twelve years) were further submitted to an oral calcium load test. Eighteen patients (40%) had AH, 7 (15.5%) RH and 20 (44.4%) could not be classified as having AH or RH [indeterminant (ID) idiopathic hypercalciuria group]. Intravenous pyelography or ultrasound were normal in all children. The oral calcium load test may be useful in characterizing the subtype of IH in some children; however, a great number of the IH children were characterized as indeterminant. Also hyperuricosuria, recently described as another metabolic disturbance associated with hematuria, may be an important cause of recurrent hematuria in children.     

Clinical presentation and natural course of idiopathic hypercalciuria in children

Idiopathic hypercalciuria (IHC) has been reported mainly in children with hematuria in the 1980s and early 1990s, when renal sonography was just becoming routine. The presence of microcalculi, i.e., of hyperechogenic spots <3 mm in diameter in renal calyces, was not taken into account in those studies. We attempted to outline clinical presentation and natural course of IHC not only in children with hematuria, but also in those with dysuria and/or recurrent abdominal/flank pain and a family history of nephrolithiasis, taking into account the finding of microcalculi. We analyzed retrospectively the data at diagnosis from 74 consecutive children aged 2.4–18 years (mean 8.6) with IHC (calciuria 4.1–15.1 mg kg^–1 24 h^–1, mean 6.1) and the outcome of 30 of them who were followed ≥1 years (mean 3.2) with no specific therapy. At diagnosis, 38 patients (51%) had no hematuria, 42 (57%) had microcalculi and four (5%) had calculi. Of the patients with normal urinalysis, 71% had microcalculi or stones. The subjects with microcalculi and those with stones were significantly older than those without microcalculi and stones (P=0.004 and 0.007). A normal urinalysis at our evaluation and a history of abdominal/flank pain were significantly more frequent in patients with microcalculi than in those without (P=0.02 and 0.0001, respectively). During the follow-up, four of 30 patients formed stones 1–3 years after first diagnosis of IHC. More than half of children with IHC have microcalculi. The risk of formation of microcalculi or stones increases with age. The lack of hematuria does not exclude the presence of microcalculi or calculi. Hypercalciuria has to be suspected in children with dysuria and/or recurrent abdominal/ flank pain and a family history of nephrolithiasis, even when they have no hematuria. Received: 13 December 1999 / Revised: 26 April 2000 / Accepted: 19 May 2000     

BMP2及Msx2在特发性高钙尿肾结石患者肾乳头组织表达的研究

目的：研究骨形态发生蛋白2（BMP2）及成骨样细胞转录因子Msx2在特发性高钙尿（IH）肾结石患者肾乳头组织中表达以及探讨其在IH患者结石形成中作用机制。方法：筛选特发性高钙尿肾结石患者8例（IH组）,排除各种已知可能影响血清钙或者尿钙的继发疾病;选择同期因肾肿瘤或非结石所致的无功能肾需行肾切除术的患者8例（NC组）。分别取16例患者肾乳头组织若干,各标本应用实时荧光定量PCR检测BMP2和Msx2mRNA的表达,并应用Westernblot测定两组蛋白质表达水平。结果：IH组BMP2的mRNA表达量为（1．491±0．121）,而NC组BMP2的tuRNA为（1．032±0．034）,两组间表达量差异有统计学意义（P〈0．05）;而1H组与NC组Msx2的mRNA表达量分别为（1．432±0．091）和（1．015±0．017）,两组数据差异有统计学意义（P〈0．05）。Westernblotting检测BMP2蛋白提示NC组和IH组蛋白质表达量分别为（1．475±0．042）和（1．681±0．153）,两组数据差异有统计学意义（P〈0．05）;测定Msx2蛋白水平表达显示NC组为（1．531±0．134）,而IH组（1．603±0．156）,两者差异无统计学意义（P〉0．05）。结论：特发性高钙尿（IH）肾结石患者肾乳头BMP2和Msx2mRNA表达增强为间质异位钙化特征,BMP2信号通路在特发性高钙尿结石患者Randall钙斑形成中具有一定作用。     

Evidence for altered renal tubule function in idiopathic calcium stone formers

Patients who form calcium kidney stones often have metabolic disorders such as idiopathic hypercalciuria (IH) that reflect abnormalities in mineral handling in the kidney. Renal handling of calcium is altered by ingestion of nutrients such as carbohydrates, protein, and sodium, and patients with IH appear to be more sensitive to these stimuli. Studies using probes such as diuretics or lithium clearance have the ability to clarify which nephron segments are involved in the altered renal calcium transport with nutrient seen in IH. Studies in the genetic hypercalciuric rat demonstrate alterations in both proximal tubule and thick ascending limb calcium reabsorption. Similar studies in humans have begun to provide evidence about the corresponding abnormalities in stone formers with IH. A pattern of altered renal tubule transport in calcium stone formers is suggested by the frequency of such findings as decreased tubular maximal reabsorption of phosphate and abnormal urine acidification as well as hypercalciuria in such patients, not explained by monogenic transport abnormalities.     

Irritability and dysuria in infants with idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) is being diagnosed with increasing frequency in the pediatric population and occurs in approximately 2.9–6.2% of normal children. The majority of children with IH are asymptomatic; however, the most common clinical presentation is that of isolated hematuria (gross or microscopic). The prevalence, presentation and clinical course of IH is less well established in infants. We have recently seen two young infants with IH who had dysuria on presentation. Their hypercalciuria was difficult to manage and required frequent manipulations of drug therapy and diet restrictions. These cases emphasize the importance of evaluating infants with dysuria and irritability for IH, even in the absence of hematuria. Further studies are needed to establish the prevalence and classical presentation of IH in this population, and to determine the necessary duration of therapy.     

Urolithiasis associated with hypercalciuria

Fifty male patients with urolithiasis (UL), associated with idiopathic hypercalciuria (IH), were studied in comparison to a group of 18 male normocalcemic patients with inactive calcium stone disease of unknown etiology. In the group of IH-UL, in addition to hypercalciuria, statistically significant hyperphosphaturia with decreased tubular reabsorption of phosphate and hyperuricemia were observed; there was a tendency to hypophosphatemia although non-significant. In 36% of the IH-UL patients the first episode of renal colic appeared at age 40 to 50. Thirty-eight per cent of the IH-UL patients had recurrent stone formation. Twenty per cent of the IH-UL patients had a family history of urolithiasis. Forty-six per cent of all stones contained oxalate in addition to calcium, and 25% of the stones contained oxalate and phosphate.     

No evidence for point mutations of the calcium-sensing receptor in familial idiopathic hypercalciuria.

BACKGROUND: Idiopathic hypercalciuria (IH) is frequently associated with nephrolithiasis. As 40% of patients have a positive familial history of IH, an autosomal dominant mode of inheritance has been suggested. Numerous genes have been studied in this regard but none have been found to be linked to IH. Mutation of the calcium-sensing receptor (CaR) has never been studied. Therefore, we conducted a study to detect such mutations. METHODS: Seven families with IH and nephrolithiasis were recruited in a prospective study. Forty-two family members underwent 24-h urine calcium measurement. Twenty-five of them with 24-h hypercalciuria also underwent extensive metabolic evaluation. Blood samples were collected in one or two affected family members in each family and exons 2-7 of the CaR gene were sequenced. RESULTS: In the seven families, at least one parent and more than half of the children had hypercalciuria (21/30), consistent with autosomal dominant inheritance. Among the nine affected family members whose CaR gene has been studied, all nine had absorptive hypercalciuria, three also had fasting hypercalciuria, and one had renal phosphorous leak. No mutation of the CaR gene was detected in these seven families. Two previously reported polymorphisms were detected, each of them in five families: A986S and C-to-T change at -60 in intron 5. CONCLUSION: In these seven families, IH is not related to the CaR gene mutation. Although we cannot exclude that point mutations can be found in other families, familial IH does not seem to be generally associated with CaR mutation.     

Novel NaPi-IIc mutations causing HHRH and idiopathic hypercalciuria in several unrelated families: long-term follow-up in one kindred

Homozygous and compound heterozygous mutations in SLC34A3, the gene encoding the sodium-dependent co-transporter NaPi-IIc, cause hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a disorder characterized by renal phosphate-wasting resulting in hypophosphatemia, elevated 1,25(OH)(2) vitamin D levels, hypercalciuria, rickets/osteomalacia, and frequently kidney stones or nephrocalcinosis. Similar albeit less severe biochemical changes are also observed in heterozygous carriers, which are furthermore indistinguishable from those encountered in idiopathic hypercalciuria (IH). We now searched for SLC34A3 mutations (exons and introns) in two previously not reported HHRH kindreds, which resulted in the identification of three novel mutations. The affected members of kindred A were compound heterozygous for two different mutations, c.1046_47del and the intronic mutation c.560+23_561-42del, while the index case in kindred B was homozygous for the nonsense SLC34A3 mutation c.1764C>G (p.Y588X). The patient in kindred C was diagnosed with IH because of bilateral medullary nephrocalcinosis, suppressed PTH levels, and hypercalciuria; she was found to have a novel heterozygous c.1571_1880del mutation. The HHRH patients in kindred A were treated for up to 7years with oral phosphate, which led to reversal of hypophosphatemia, hypercalciuria, and prevention or healing of the mild bone abnormalities. PTH levels were normal throughout the observation period, while 1,25(OH)(2) vitamin D levels remained elevated and may thus be helpful for assessing treatment efficacy and patient compliance in HHRH.     

Caliceal diverticular calculi: is there a role for metabolic evaluation?

PURPOSE: We report our experience with the treatment and incidence of metabolic abnormalities in patients presenting with caliceal diverticular stones. MATERIALS AND METHODS: We retrospectively evaluated 49 patients with caliceal diverticular stones (group 1) and 44 with simple renal stones (group 2). Each group successfully underwent percutaneous treatment. Mean stone size was 1.7 and 2.5 cm. in groups 1 and 2, respectively. Metabolic evaluation was available in 25 group 1 and 22 group 2 patients. Mean followup was 73.2 and 70. 8 months, respectively. RESULTS: We achieved a stone-free rate of 95. 9% in group 1 and 100% in group 2. There was no metabolic abnormality in 75% of the group 1 patients, while 12% had type II absorptive hypercalciuria, 8% hyperuricosuric hypercalciuria and 4% hyperoxaluria. There were no metabolic abnormalities in 22.7% of the group 2 patients, while 9%, 18% and 9% had types I to III absorptive hypercalciuria, respectively, 13.6% hyperuricosuric hypercalciuria, 13.6% hyperoxaluria, 4.5% hypocitruria and 9% type II absorptive hypercalciuria associated with hypocitruria. CONCLUSIONS: Our results reveal a low incidence of associated metabolic abnormalities in patients with caliceal diverticular stones. Thus, we believe that metabolic abnormalities do not promote caliceal diverticular calculous formation.     

Metabolic risk factors in children with kidney stone disease

The evaluation of metabolic risk factor in children with renal stone disease is the basis of medical treatment aimed at preventing recurrent stone events and the growth of preexisting calculi. In this retrospective study, we evaluated the metabolic risk factors and clinical and family histories of 90 children with kidney stone disease who had been referred to our institution and subjected to clinical tests using a standardized protocol. The mean age of our pediatric patients was 10.7 years, and the male:female ratio was 1.14:1.0. Biochemical abnormalities were found in 84.4% of all cases. A single urine metabolic risk factor was present in 52.2% (n = 47) of the patients, and multiple risk factors were present in the remaining 31.1% (n = 28). Idiopathic hypercalciuria (alone or in combination) and hypocitraturia (alone or in combination) were the most frequent risk factors identified in 40 and 37.8% of these patients, respectively. Renal colic or unspecified abdominal pain were the most frequent forms of presentation (76.9%), with 97.5% of stones located in the upper urinary tract. In most patients, stone disease was confirmed by renal ultrasonography (77%). A positive family history in first-degree and second-degree relatives was found in 46.2 and 32.5% of the cases, respectively. We conclude that specific urine metabolic risk factors are found in most children with kidney stones and that hypocitraturia is as frequent as hypercalciuria. Very often there is a positive family history of renal stone disease in first- and second-degree relatives.     

Metabolic and demographic characteristics of children with urolithiasis in Western Turkey

Pediatric urolithiasis is an endemic disease in Turkey. We evaluated the clinical, radiological and metabolic features of children with urolithiasis in Western Turkey. We retrospectively reviewed the records of 85 children with urolithiasis who were followed-up between 2004 and 2010 in Pediatric Nephrology Department of Celal Bayar University, Manisa. The male/female ratio was 1.23/1. The mean age at diagnosis was 66.1 months (range 3–210 months). Family history of urolithiasis was found in 58 (68.2%) patients. 23 (27%) patients were born from consanguineous marriages. Stones were located in the upper urinary tract in 79 (92.9%) patients. In 66 (77.6%) patients, stones were single-sided and 41 (48.2%) patients had multiple stones. Calcium oxalate stones were the most common one among patients in whom stone analysis was performed (78.5%). Hypocitraturia was the most commonly detected urinary metabolic risk factor. In patients who were under 12 months of age at diagnosis, hypercalciuria was the most commonly seen urinary metabolic risk factor. At the end of follow-up period, 24 patients became free of stone disease and 4 patients had recurrence. In conclusion, metabolic abnormalities are common in pediatric stone patients and are strongly associated with recurrence. Considering that urolithiasis in children is an important risk factor for renal failure, early diagnosis, detailed metabolic evaluation and implementing appropriate treatment and follow-up protocols may prevent recurrence and renal damage.     

特发性高钙尿与骨质疏松的研究进展

特发性高钙尿症(idiopathic hypercalciuria,IH)主要有两大危害,一则影响骨代谢,容易引起骨量减少、骨质疏松,增加骨折风险;二则影响泌尿系统,主要表现为增加患肾结石风险。高钙尿引起骨质疏松及肾结石的具体机制尚不明确。现有的研究表明核因子κB受体活化因子配体(RANKL)/核因子κB受体活化因子(RANK)/护骨素(OPG)通路激活可能是IH患者引起骨质疏松的主要机制之一。雌激素缺乏会引起尿钙升高、骨量减少,是高钙尿及骨质疏松的重要病因。高钙尿症还可能通过单核细胞趋化因子-1(MCP-1)等细胞因子的增加从而引起骨量减少。对遗传因素的研究中发现了许多与高钙尿及骨量减少相关联的基因,主要包括降钙素受体基因、瞬时感受器电位阳离子通道香草精受体5基因、维生素D受体基因。但对上述一些基因型与骨质疏松的研究存在不同的结论,而雌激素缺乏还可通过影响瞬时感受器电位阳离子通道香草精受体5基因的表达起作用,因此遗传因素可能成为未来研究的热点。     

The use of a test for the differential diagnosis of hypercalciuria.

28 renal stone formers (18 men and 10 women) with idiopathic hypercalciuria (IH) and 27 controls have been subjected to a test proposed for the diagnosis of absorptive, resorptive and renal hypercalciurias. Fasting serum calcium concentration, urinary calcium and cyclic AMP excretion were measured after overnight fasting and an oral load of calcium. Absorptive hypercalciuria was demonstrated in 14 patients. High fasting urinary calcium first suggested resorptive or renal hypercalciurias in 5 other patients, but since fasting urinary calcium was normalized following cellulose phosphate therapy, absorptive hypercalciuria was more likely. Renal hypercalciuria was a possibility in 1 single case. Both fasting and post-load urinary calcium were normal in 7 men and 1 woman. The test did not appear as useful as expected since it was of no diagnostic value in about 30% of the cases and erroneously suggested resorptive or renal hypercalciuria in about 15% of the cases. On the other hand it indicated that absorptive IH is common and renal IH exceptional.     

The Relation Between Bone and Stone Formation

Hypercalciuria is the most common metabolic abnormality found in patients with calcium-containing kidney stones. Patients with hypercalciuria often excrete more calcium than they absorb, indicating a net loss of total-body calcium. The source of this additional urinary calcium is almost certainly the skeleton, the largest repository of calcium in the body. Hypercalciuric stone formers exhibit decreased bone mineral density (BMD), which is correlated with the increase in urine calcium excretion. The decreased BMD also correlates with an increase in markers of bone turnover as well as increased fractures. In humans, it is difficult to determine the cause of the decreased BMD in hypercalciuric stone formers. To study the effect of hypercalciuria on bone, we utilized our genetic hypercalciuric stone-forming (GHS) rats, which were developed through successive inbreeding of the most hypercalciuric Sprague-Dawley rats. GHS rats excrete significantly more urinary calcium than similarly fed controls, and all the GHS rats form kidney stones while control rats do not. The hypercalciuria is due to a systemic dysregulation of calcium homeostasis, with increased intestinal calcium absorption, enhanced bone mineral resorption, and decreased renal tubule calcium reabsorption associated with an increase in vitamin D receptors in all these target tissues. We recently found that GHS rats fed an ample calcium diet have reduced BMD and that their bones are more fracture-prone, indicating an intrinsic disorder of bone not secondary to diet. Using this model, we should better understand the pathogenesis of hypercalciuria and stone formation in humans to ultimately improve the bone health of patients with kidney stones.     

Nephrocalcinosis in three siblings with idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) associated with nephrocalcinosis was found in three of six siblings. After the three affected children were maintained on a low-calcium diet, they demonstrated increasing hypercalciuria, parathyroid hormone, and vitamin D₃ levels. An oral calcium loading test was not necessary to diagnose renal IH. During treatment with hydrochlorothiazide, the calcium excretion was normalized. These patients are remarkable because nephrocalcinosis is generally regarded as a rare complication of renal IH. Moreover, the fact that three of six siblings are affected raises the question of whether the renal form of IH is genetically distinct from other forms of IH. Received January 3, 1997; received in revised form July 23, 1997; accepted July 30, 1997     

Evaluation of serum osteocalcin in patients with urolithiasis

Serum osteocalcin, also called bone gla protein, is one of sensitive and specific markers for metabolic bone diseases. Current evidence suggests that the protein may be involved in the regulation of calcium homeostasis in bone. We measured serum osteocalsin levels by radioimmunoassay in 100 patients with urolothiasis, especially in calcium containing stone formers and evaluated the influence of bone metabolism on the formation of calcium-containing stones. Although serum osteocalcin levels in most patients were normal, those of two male and four female patients were high. We considered that they were patients with renal hypercalciuria and secondary hyperparathyroidism and in them the formation of calcium containing stones were influenced by disorder of bone metabolism. In addition, we suggest that serum osteocalcin levels may be available index for the effect of treatment in stone formers with renal hypercalciuria and bone disease.