Calcium oxalate urolithiasis in mice lacking anion transporter Slc26a6

Urolithiasis is one of the most common urologic diseases in industrialized societies. Calcium oxalate is the predominant component in 70-80% of kidney stones, and small changes in urinary oxalate concentration affect the risk of stone formation. SLC26A6 is an anion exchanger expressed on the apical membrane in many epithelial tissues, including kidney and intestine. Among its transport activities, SLC26A6 mediates Cl(-)-oxalate exchange. Here we show that mutant mice lacking Slc26a6 develop a high incidence of calcium oxalate urolithiasis. Slc26a6-null mice have significant hyperoxaluria and elevation in plasma oxalate concentration that is greatly attenuated by dietary oxalate restriction. In vitro flux studies indicated that mice lacking Slc26a6 have a defect in intestinal oxalate secretion resulting in enhanced net absorption of oxalate. We conclude that the anion exchanger SLC26A6 has a major constitutive role in limiting net intestinal absorption of oxalate, thereby preventing hyperoxaluria and calcium oxalate urolithiasis.

Disruption of the caveolin-1 gene impairs renal calcium reabsorption and leads to hypercalciuria and urolithiasis

Using LoxP/Cre technology, we generated a knockout mouse homozygous for a null mutation in exon 2 of Cav1. In male Cav1-/- animals, we observed a dramatic increase in the incidence of urinary calcium stone formation. In 5-month-old male mice, the incidence of early urinary calculi was 67% in Cav1-/- mice compared to 19% in Cav1+/+ animals. Frank stone formation was observed in 13% of Cav1-/- males but was not seen in Cav1+/+ mice. Urine calcium concentration was significantly higher in Cav1-/- male mice compared to Cav1+/+ mice. In Cav1-/- mice, distal convoluted tubule cells were completely devoid of Cav1 and the localization of plasma membrane calcium ATPase was disrupted. Functional studies confirmed that active calcium absorption was significantly reduced in Cav1-/- compared to Cav1+/+ male mice. These results demonstrate that disruption of the Cav1 gene promotes the progressive steps required for urinary calcium stone formation and establish a new mouse model for urinary stone disease.

Regulation of renal calcium receptor gene expression by 1,25-dihydroxyvitamin D3 in genetic hypercalciuric stone-forming rats

Hypercalciuria in inbred genetic hypercalciuric stone-forming (GHS) rats is due, in part, to a decrease in renal tubule Ca reabsorption. Activation of the renal Ca receptor (CaR) may decrease renal tubule Ca reabsorption and cause hypercalciuria through suppression of Ca-sensitive potassium channel activity. Because the rat renal CaR gene is regulated by extracellular calcium and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and GHS rats have increased renal vitamin D receptor content, the current study was undertaken to determine the level of CaR gene expression in GHS rat kidney and whether CaR gene expression is regulated by 1,25(OH)2D3. Male GHS and normal control (NC) rats were fed a Ca-sufficient diet (0.6% Ca). Western blotting revealed a four-fold increase in CaR protein in GHS rat renal tissue, and 1,25(OH)2D3 administration increased renal CaR in both GHS and NC rats. Northern blot analysis of extracts of renal cortical tissue from GHS and NC rats revealed a major 7-kb transcript of CaR and a more modest 4-kb transcript, both of which were readily detectable. Both Northern blotting and real-time reverse transcription-PCR revealed increased basal CaR mRNA expression levels in GHS rat kidney. 1,25(OH)2D3 administration increased renal CaR mRNA levels 2.0- and 3.3-fold in GHS and NC rats, respectively. Despite the greater incremental increase by 1,25(OH)2D3 in NC rats, CaR mRNA levels remained higher in GHS rat kidney, and the elevation was more sustained. 1,25(OH)2D3 increased CaR mRNA through both elevated CaR gene expression and prolonged tissue half-life. These results demonstrate that GHS rats have high levels of CaR gene expression and CaR protein that may contribute to the hypercalciuria and calcium nephrolithiasis.

Treatment of cystinuria

Cystine urolithiasis is the only clinical expression of cystinuria, an autosomal recessive genetic defect of the transepithelial transport of cystine and other dibasic amino acids in the kidney. Stones form due to the increased excretion of cystine, which is poorly soluble at normal urine pH. Cystine stones are often resistant to extracorporeal shock wave lithotripsy, so that percutaneous surgery or ureteroscopy are the preferred techniques of stone extraction. Medical preventative treatment is based on high diuresis (>/=1.5 l/m(2) per day) well distributed throughout the day and night, and urine alkalinization up to pH 7.5 by means of sodium bicarbonate and/or potassium citrate. When these basal measures are ineffective at preventing stone recurrence or dissolving pre-existing stones, sulfhydryl agents such as D-penicillamine or tiopronin, which form highly soluble mixed disulfides with cystine moieties, are to be added to urine dilution and alkalinization, especially when cystine excretion is in excess of 750 mg/day (3 mmol/day). Frequent clinical and ultrasound follow-up is needed to encourage patient compliance and assess efficacy and tolerance of treatment.

Slc7a9-deficient mice develop cystinuria non-I and cystine urolithiasis

Cystinuria is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids that results in urolithiasis of cystine. Cystinuria is caused by defects in the amino acid transport system b0,+ (i.e. the rBAT/b0,+AT heteromeric complex). Mutations in SLC3A1, encoding rBAT, cause cystinuria type A, characterized by a silent phenotype in heterozygotes (phenotype I). Mutations in SLC7A9, encoding b0,+AT, cause cystinuria type B, in which heterozygotes in most cases hyperexcrete cystine and dibasic amino acids (phenotype non-I). To facilitate in vivo investigation of b0,+AT in cystinuria, Slc7a9 knockout mice have been generated. Expression of b0,+AT protein is completely abolished in the kidney of Slc7a9-/- mice ('Stones'). In contrast, Stones expressed significant amounts of rBAT protein, which is covalently linked to unidentified light subunit(s). Stones mice present a dramatic hyperexcretion of cystine and dibasic amino acids, while Slc7a9+/- mice show moderate but significant hyperexcretion of these amino acids (phenotype non-I). Forty-two per cent of Stones mice develop cystine calculi in the urinary system. Calculi develop during the first month of life and grow throughout the life span of the animals. Histopathology in kidney reveals typical changes for urolithiasis (tubular and pelvic dilatation, tubular necrosis, tubular hyaline droplets and chronic interstitial nephritis). The fact that some Stones mice, generated in a mixed genetic background, develop cystine calculi from an early age, while others do not develop them in their first year of life, suggests the involvement of modifier genes in the lithiasis phenotype. Thus, Stones provide a valid model of cystinuria which can be used in the study of genetic, pharmacological and environmental factors involved in cystine urolithiasis.

Pediatric urolithiasis--evaluation of risk factors in 95 children

OBJECTIVE

Pediatric urolithiasis is a rarely encountered pathology, except in endemic areas such as Turkey. As a recurrent pathology which may reveal functional as well and morphologic changes in the urinary tract, metabolic and environmental factors, in addition to urogenital abnormalities, should be evaluated thoroughly in each patient. In this prospective study, the patient and family histories of 95 children with stone disease were evaluated, together with serum and urine risk factors.

MATERIAL AND METHODS

Between 1996 and 2001, 95 children (25 females, 70 males; mean age 7.3 years; age range 0.6-15 years) referred to our department with urolithiasis were evaluated. All patients were investigated with respect to stone localization, associated abnormalities, urinary tract infection (UTI), positive family history and serum and urine risk factors. In addition to standard risk factors (hypocitraturia, hypercalciuria, hyperoxaluria, hyperuricosuria, hypomagnesuria), diet and 24-h urine volume were also assessed in all children. Children with cystinuria were excluded from the study.

RESULTS

Stone size ranged from 0.3 to 3.3 cm, with an average value of 2.0 cm. The localization of the stones was classified as unilateral single stone in 37 patients, multiple unilateral stones in six and bilateral multiple stones in 27. Hypocitraturia was the commonest risk factor detected in our patients. A positive family history was present in 51 cases (54%). In addition, UTI was present in 59 cases (62%) and 67 cases had a previous history of recurrent UTI. Associated urogenital abnormality was detected in nine cases (9.4%). There were significant correlations between stone size and urinary citrate excretion (p < 0.05) and between the presence of UTI and urinary phosphate excretion (r = 0.59, p = 0.047). Treatments used were open surgery in seven (7.3%) cases, extracorporeal shock-wave lithotripsy in 39 (41%) and endoscopic surgery in 20 (21%). Following these procedures, 39 (41%) patients were completely stone-free, 11 (11%) had residual stones (<5 mm in diameter) and 12 (14.8%) passed the stone(s) spontaneously. During follow-up, regrowth was seen in four (4.2%) patients and stone recurrence was noted in a further four (4.2%).

CONCLUSIONS

In addition to stone removal, treatment of pediatric urolithiasis requires a thorough metabolic and environmental evaluation of all patients on an individual basis. Obstructive pathologies have to be corrected immediately and apparent metabolic abnormalities should also be treated. Children with a positive family history should be followed carefully with respect to stone recurrence. Urine volume increases in parallel with body mass index and medical therapeutic agents which increase urine citrate levels should be encouraged.

The association of idiopathic hypercalciuria and asymptomatic gross hematuria in children

Seven children with asymptomatic gross hematuria are described. Six had recurrent hematuria; one had a single episode. Occasional global glomerulosclerosis and/or mesangial electron dense deposits were present in the three patients in whom renal biopsy was performed; the changes were felt to be insufficient to account for the hematuria. None of the patients had urolithiasis or any significant urinary tract abnormality. One was an adopted child; a family history of urolithiasis was obtained in the other six. Idiopathic hypercalciuria was documented in six patients; the seventh subsequently passed a calcium oxalate calculus. One patient is 10 weeks of age at the time of this submission. Of the remainder, three patients received no specific therapy; renal calculi developed six months, six years, and eight years later. Three patients were treated with a thiazide diuretic soon after onset of hematuria and confirmation of idiopathic hypercalciuria; there was complete cessation of hematuria within five days with no recurrence as long as therapy was continued. We suggested that measurement of urinary calcium excretion as part of the initial evaluation of a child with gross hematuria may, in some cases, obviate invasive investigations and allow for effective therapy.

Genetic and clinical studies on 19 families with adenine phosphoribosyltransferase deficiencies

Adenine phosphoribosyltransferase (APRT) deficiency leading to 2,8-dihydroxyadenine (DHA) urolithiasis has been considered a rare cause of urolithiasis and renal insufficiency. We have examined samples from 19 Japanese families with DHA lithiasis. In 79% of the families, patients only partially lacked hemolysate APRT activities, clearly contrasting with the complete deficiency in all the patients from non-Japanese families so far reported. All patients with DHA lithiasis were homozygotes for defective APRT genes, whether the deficiency was complete or partial. In family studies we found two symptomatic and four asymptomatic homozygous family members. The segregation figures are compatible with the hypothesis of a simple autosomal recessive mode of inheritance. By analyzing the data stored by a large clinical laboratory in Japan, we estimated that 0.00368% of the general population has DHA lithiasis. These data indicate that more than 1% of the general population possess mutant alleles of the APRT gene as heterozygotes. Our present studies indicate that most of the patients with this disease are undiagnosed in Japan, and probably in other countries also.

Studies on the prevalence and epidemiology of urinary stone disease in men in Leeds

A postal survey among 2% of men in Leeds showed that the prevalence of urinary stone disease is 3.8%. The prevalence of upper urinary tract and spontaneously passed stones increases progressively from 0.7% in social class 5 to 5.0% in social class 1 but that of bladder stones (0.7% in the group as a whole) is independent of social class. There is an initial peak of upper urinary tract and spontaneously passed stones commencing at age 20 and having a projected prevalence at age 90 of 5.7% and a second peak of bladder stones, commencing about age 50, with a projected prevalence of 1.9%. The prevalence of stone disease increases according to the order: single less than divorced/separated less than married less than widowed men. A family history of stones tends to be higher amongst relatives of stone-formers than amongst the corresponding relatives of control subjects, the male/female ratio being 2:1. The occurrence of urinary stones is significantly associated with that of gallstones, high blood pressure, backache, arthritis and gout but not with that of peptic ulcer, diabetes, thyroid disease or bronchitis.

Potential mechanisms of marked hyperoxaluria not due to primary hyperoxaluria I or II

BACKGROUND

Hyperoxaluria may be idiopathic, secondary, or due to primary hyperoxaluria (PH). Hepatic alanine:glyoxylate aminotransferase (AGT) or glyoxylate/hydroxypyruvate reductase (GR/HPR) deficiency causes PHI or PHII, respectively. Hepatic glycolate oxidase (GO) is a candidate enzyme for a third form of inherited hyperoxaluria.

METHODS

Six children were identified with marked hyperoxaluria, urolithiasis, and normal hepatic AGT (N = 5) and GR/HPR (N = 4). HPR was below normal and GR not measured in one. Of an affected sibling pair, only one underwent biopsy. GO mutation screening was performed, and dietary oxalate (Diet(ox)), enteric oxalate absorption (EOA) measured using [13C2] oxalate, renal clearance (GFR), fractional oxalate excretion (FE(ox)) in the children, and urine oxalate in first-degree relatives (FDR) to understand the etiology of the hyperoxaluria.

RESULTS

Mean presenting age was 19.2 months and urine oxalate 1.3 +/- 0.5 mmol/1.73 m2/24 h (mean +/- SD). Two GO sequence changes (T754C, IVS3 - 49 C>G) were detected which were not linked to the hyperoxaluria. Diet(ox) was 42 +/- 31 mg/day. EOA was 9.4 +/- 3.6%, compared with 7.6 +/- 1.2% in age-matched controls (P = 0.33). GFR was 90 +/- 19 mL/min/1.73 m2 and FE(ox) 4.2 +/- 1.4. Aside from the two brothers, hyperoxaluria was not found in FDR.

CONCLUSIONS

These patients illustrate a novel form of hyperoxaluria and urolithiasis, without excess Diet(ox), enteric hyper-absorption, or hepatic AGT, GR/HPR deficiency. Alterations in pathways of oxalate synthesis, in liver or kidney, or in renal tubular oxalate handling are possible explanations. The affected sibling pair suggests an inherited basis.

A mouse model for cystinuria type I

Cystinuria, one of the most common inborn errors of metabolism in humans, accounts for 1-2% of all cases of renal lithiasis. It is caused by defects in the heterodimeric transporter system rBAT/b0,+AT, which lead to reduced reabsorption of cystine and dibasic amino acids through the epithelial cells of the renal tubules and the intestine. In an N-ethyl-N-nitrosourea mutagenesis screen for recessive mutations we identified a mutant mouse with elevated concentrations of lysine, arginine and ornithine in urine, displaying the clinical syndrome of urolithiasis and its complications. Positional cloning of the causative mutation identified a missense mutation in the solute carrier family 3 member 1 gene (Slc3a1) leading to an amino acid exchange D140G in the extracellular domain of the rBAT protein. The mouse model mimics the aetiology and clinical manifestations of human cystinuria type I, and is suitable for the study of its pathophysiology as well as the evaluation of therapeutic and metaphylactic approaches.

Familial calcium stone disease: TaqI polymorphism and the vitamin D receptor

BACKGROUND AND OBJECTIVE

Calcium nephrolithiasis has a strong familial component. However, to date, no specific genetic abnormality has been identified. Allelic variation in the vitamin D receptor (VDR) gene has been suggested as a partial explanation of differential calcium absorption or excretion in these patients. Polymorphism of this gene has been associated with altered vitamin D activity and has been implicated in osteoporosis and prostate cancer. We propose that a similar association may be found between familial hypercalciuric stone disease and the VDR.

SUBJECTS AND METHODS

Genomic DNA was isolated from 37 controls and 19 patients with hypercalciuria (> 250 mg/24 hours) and a family history of nephrolithiasis. A 740-basepair segment of the VDR gene was amplified by polymerase chain reaction, digested with TaqI endonuclease, and resolved by gel electrophoresis. Alleles were classified as "T" if only one TaqI site was present and "t" if two were present. A simplified strength of family history score (FHS) was computed by adding 2 and 1 points, respectively, for each first- and second-degree relative affected by stone disease.

RESULTS

No difference in allelic or genotypic frequencies between the study and control groups was present. In the stone group, a significant association was found between the strength of the family history and the TT genotype. Patients with this genotype had an average FHS of 4.0, whereas the mean FHS for the Tt and tt genotypes was 2.0 and 1.8, respectively (P < 0.05). Nonsignificant trends of the TT genotype toward a higher number of stone episodes (19 v 13 and 3) and higher 24-hour urine calcium excretion (408 v 297 and 353 mg) were also noted in the study group.

CONCLUSION

The results suggest that the TT genotype is associated with more aggressive stone disease, both within families and with respect to recurrence. Quantifying the risk of calcium stone disease through DNA markers has potential application in determining the risk of a patient's family members for nephrolithiasis or a patient's risk of recurrence. This information may have therapeutic implications with regard to the rigor of medical therapy and frequency of follow-up.

Clinical and functional characterization of URAT1 variants

Idiopathic renal hypouricaemia is an inherited form of hypouricaemia, associated with abnormal renal handling of uric acid. There is excessive urinary wasting of uric acid resulting in hypouricaemia. Patients may be asymptomatic, but the persistent urinary abnormalities may manifest as renal stone disease, and hypouricaemia may manifest as exercise induced acute kidney injury. Here we have identified Macedonian and British patients with hypouricaemia, who presented with a variety of renal symptoms and signs including renal stone disease, hematuria, pyelonephritis and nephrocalcinosis. We have identified heterozygous missense mutations in SLC22A12 encoding the urate transporter protein URAT1 and correlate these genetic findings with functional characterization. Urate handling was determined using uptake experiments in HEK293 cells. This data highlights the importance of the URAT1 renal urate transporter in determining serum urate concentrations and the clinical phenotypes, including nephrolithiasis, that should prompt the clinician to suspect an inherited form of renal hypouricaemia.

Acute kidney injury in two children caused by renal hypouricaemia type 2

BACKGROUND

Renal hypouricaemia is a heterogeneous inherited disorder characterized by impaired tubular uric acid transport with severe complications, such as acute kidney injury and nephrolithiasis. Type 1 is caused by a loss-of-function mutation in the SLC22A12 gene (OMIM #220150), while type 2 is caused by defects in the SLC2A9 gene (OMIM #612076).

CASE-DIAGNOSIS/TREATMENT

The cases of two children, a 12- and a 14-year-old boy with acute kidney injury (proband 1: urea 9.4 mmol/l, creatinine 226 μmol/l; proband 2: urea 11.7 mmol/l, creatinine 202 μmol/l) are described. Both are offspring of nonconsanguineous couples in the UK. The concentrations of serum uric acid were consistently below the normal range (0.03 and 0.04 mmol/l) and expressed as an increase in the fractional excretion of uric acid (46 and 93 %).

CONCLUSIONS

A sequencing analysis of the coding region of uric acid transporters SLC22A12 and SLC2A9 was performed. Analysis of genomic DNA revealed two unpublished missense transitions, p.G216R and p.N333S in the SLC2A9 gene. No sequence variants in SLC22A12 were found. Our findings suggest that homozygous and/or compound heterozygous loss-of-function mutations p.G216R and p.N333S cause renal hypouricaemia via loss of uric acid absorption and do lead to acute kidney injury.

Novel homozygous insertion in SLC2A9 gene caused renal hypouricemia

Renal hypouricemia is a heterogeneous inherited disorder characterized by impaired uric acid handling in the renal tubules. Patients are usually asymptomatic; however, some may experience urolithiasis and/or acute kidney injury. Most of the described patients (compound heterozygous and/or homozygous) are Japanese with mutations in the SLC22A12 gene (OMIM #220150). Four patients with renal hypouricemia caused by heterozygous defects and two families with homozygous mutations in the SLC2A9 gene have been recently described (OMIM #612076). We describe the clinical history, biochemical and molecular genetics findings of a Czech family with renal hypouricemia. The concentration of serum uric acid in the proband (16-year-old Czech girl with unrelated parents) was 0.17 ± 0.05 mg/dl and expressed as an increase in the fractional excretion of uric acid (194 ± 99%). The sequencing analysis of the coding region of uric acid transporters SLC22A12, SLC2A9, SLC17A3, ABCC4 and ABCG2, was performed. Analysis of genomic DNA revealed novel one nucleotide homozygote insertion in exon 3 in the SLC2A9 gene in proband and her brother resulting in a truncated protein (p.Ile118HisfsX27). No sequence variants in other candidate uric acid transporter were found. Homozygous loss-of-function mutations cause massive renal hypouricemia via total loss of uric acid absorption; however, they do not necessarily lead to nephrolithiasis and acute kidney injury. In contrast to previously reported heterozygous patients with renal hypouricemia type 2, we did not find even slight hypouricemia and found no decrease in the FE-UA of the heterozygous parents of the reported siblings.

Severe impairment in adenine metabolism with a partial deficiency of adenine phosphoribosyltransferase

Among three unrelated patients with recurrent 2,8-dihydroxyadenine urolithiasis, two completely lacked adenine phosphoribosyltransferase (APRT) in both erythrocytes and proliferative T cells. The third patient possessed significant enzyme activities in both hemolysates and T-cell extracts at levels comparable to heterozygotes for complete APRT deficiency. Despite significant APRT activities in cell extracts, cultured T cells from the third patient were at least 100-fold more resistant than normal T cells to an adenine analog, 6-methylpurine, whose cytotoxicity is dependent on APRT. These data indicate that APRT activity in T cells from the third patient is positive in cell extracts, but apparently not operating in viable cells. Although the cells from the patients with complete APRT deficiency were as resistant to 6-methylpurine as the cells from the third patient, the cells from the heterozygotes for complete APRT deficiency were almost as sensitive as normal T cells. Therefore, adenine metabolism in the third patient but not in the heterozygotes seems to be as severely impaired as in the patients with complete APRT deficiency, which is quite consistent with the clinical manifestations in these individuals.

Association of the vitamin D receptor gene start codon Fok I polymorphism with calcium oxalate stone disease

OBJECTIVE

To assess the use of Fok I polymorphism (the most frequent polymorphism, at the start codon of the vitamin D receptor gene, VDR) as a convenient genetic marker in identifying the cause of urolithiasis.

PATIENTS, SUBJECTS AND METHODS

A normal control group of 90 healthy subjects and 146 patients with calcium oxalate stones were examined. Using polymerase chain reaction (PCR)-based restriction analysis, the relationship between Fok I polymorphism and urolithiasis was evaluated. An unexcisable length of 265 bp was identified (allele CC) and two fragments (169 bp and 96 bp) identified as excisable lengths (allele TT).

RESULTS

There was a statistically significant difference between the groups (chi-square test, P < 0.05) for the genotype of the VDR Fok I start codon polymorphism. The odds ratio (95% confidence interval) for the C allele in those at risk of stone disease was 1.672 (1.149-2.432).

CONCLUSIONS

These results suggest that the VDR Fok I start codon polymorphism may be a good candidate for a genetic marker in calcium oxalate stone disease.

Pediatric urolithiasis in the 1970s

We studied retrospectively 38 children who presented with urolithiasis between 1970 and 1977. The sex ratio was 1:1 and the mean age was 9.4 years. A positive family history was found in 36 per cent. Urinary tract abnormalities predisposing to infective urolithiasis was found in 7 children (18 per cent) but required voiding cystography for detection in 5. Hypercalcemia was found in 3 of 32 (8 per cent), while 28 of the 38 patients (74 per cent) had idiopathic urolithiasis. Idiopathic hypercalciuria was found in 5 of 13 patients (38 per cent) with idiopathic urolithiasis. Investigation of urolithiasis in children should include voiding cystography and measurement of urine calcium, as well as oxalate and uric acid, under home diet conditions.

Long-term outcome of paediatric patients with hereditary tubular disorders

BACKGROUND

An increasing number of children with hereditary tubular disorders (HTD) reach adult life due to diagnostic and therapeutic advances which results in growing need to manage these patients by adult centres. Data on the prevalence and the late clinical problems of these patients are limited.

METHODS

We observed 177 paediatric patients with isolated or complex HTD between 1969 and 1994. The median age at the time of diagnosis was 3 (range 0-18) years and the median observation period 10 (range 1-43) years. The long-term outcomes with respect to renal function, bone disease, and body growth were analyzed.

RESULTS

The prevalence of HTD was 3.2% of all patients observed in our renal unit and 14% of those patients with chronic renal failure and/ or end-stage renal disease. The three most frequent disorders observed were nephropathic cystinosis (n = 34), X-linked hypophosphataemic rickets (n = 26), and idiopathic hypercalciuria (n = 17). At the last observation, 12% of the patients with isolated HTD and 30% of those with complex HTD had developed preterminal chronic renal failure; end-stage renal disease was observed in 5 and 25%, respectively (p < 0.001). Progressive disease occurred mainly in patients having cystinosis, primary hyperoxaluria, the syndrome of hypomagnesaemia/hypercalciuria, primary Fanconi syndrome, Fanconi-Bickel syndrome, and methylmalonic aciduria. Nephrocalcinosis was found in 42%, urolithiasis in 14%, bone deformities and/or fractures in 28%, and other extrarenal alterations in 29% of all patients. The median body height at last observation was 2.0 SD below the normal mean (range from -10.4 to +2. 6), and the adult height was subnormal in 48% of 67 grown-up patients. Growth retardation was more severe in complex than in isolated HTD. The mortality decreased from 17% in 1969-1981 to 12% in 1982-1994.

CONCLUSION

Although HTD are rare nephropathies, their frequently progressive course associated with extrarenal complications requires the attention of nephrologists beyond the paediatric age.

Idiopathic hypercalciuria in children. Classification, clinical manifestations and outcome

Between 1981 and 1983, 49 children aged 2 to 15 years were diagnosed as having idiopathic hypercalciuria (IH). They were divided into 3 groups based on their response to dietary manipulation: group I (32/49) had absorptive hypercalciuria; group II (8/49) had renal hypercalciuria and group III (6/49) had sodium-dependent hypercalciuria. Response to diet was more reliable than Pak's test in differentiating between the three groups. A control group (CG) of 45 healthy, age matched children determined baseline levels for all metabolic parameters. At the time of presentation IH children did not differ from the CG in height or weight. Fifty percent of IH children had first degree relatives with urolithiasis. Yet, only 16% of the IH children had urolithiasis, the majority presenting with gross hematuria and urinary tract infections (UTI). With few exceptions the clinical symptoms resolved when urine calcium excretion was controlled. Severe calcium restriction in a few patients produced osteoporosis and delayed bone age although growth velocity was unaffected. Thiazide therapy in a few patients produced some metabolic derangements. The authors conclude that IH in childhood is a benign disease which may present with UTI or hematuria. They further propose a new classification method based on response to dietary manipulation.

Heterozygous cystinuria and calcium oxalate urolithiasis

Many variables are known to be associated with the formation of calcium oxalate urolithiasis but none is essential for the initiation or growth of stones. It is likely that the predisposition to stone formation is related to multiple factors. We herein describe still another metabolic state that seems to predispose to calcium oxalate stone disease, namely heterozygosity for cystinuria. Cystine screening tests were done on 24-hour urine specimens obtained from 126 patients in whom recurrent calcium oxalate stones form and 84 controls and quantitative amino acid determinations were done on all positive specimens. Of those studied 17 of 126 stone patients and 1 of 84 controls were heterozygous cystinurics. A test of the differences between the relative frequencies of cystinuria heterozygotes in the 2 groups with Fisher's exact test revealed them to be highly significant (p less than 0.001). Our study indicates that carrier status for 1 of the cystinuria genes predisposes to calcium oxalate stone formation but, like other factors related to urolithiasis, it is not a necessary cause of stone disease.