Single-Cell Gene Expression Analysis in Patients with Medullary Sponge Kidney and a Retrospective Study.

Objective: To establish better diagnosis thinking and provide advanced understanding of MSK, the CT imaging features, clinical characteristics, and the expression of suspected genes in the kidney spatiotemporal immune zonation and fetal renal development were investigated. Methods: 17 patients with MSK hospitalized in our hospital were selected as our research subjects. Human Phenotype Ontology, MalaCards: The Human Disease Database, GeneCards: The Human Gene Database, Human Protein Atlas, and Single Cell Expression Atlas were used to analyze this disease. Results: In our 17 patients, the incidence of MSK tended to be the same in male and female, and the onset age of MSK was probably 31-50 years old. The top one related disease of MSK was nephrocalcinosis and the most frequent phenotype related to MSK was nephrolithiasis. In addition, the expression of HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 has been implicated in both human kidney immune zonation and fetal kidney development. Conclusions: HNF1B, CLCN5, GDNF, ATP6V0A4, ATP6V1B1, LAMA2, RET, ACAN, and ABCC8 could be independent indicators for the diagnosis and preventive intervention of MSK patients, and abnormal kidney development due to mutations in key genes was the underlying cause of MSK.

Heterozygous Pkhd1C642* mice develop cystic liver disease and proximal tubule ectasia that mimics radiographic signs of medullary sponge kidney.

Heterozygosity for human polycystic kidney and hepatic disease 1 ( PKHD1) mutations was recently associated with cystic liver disease and radiographic findings resembling medullary sponge kidney (MSK). However, the relevance of these associations has been tempered by a lack of cystic liver or renal disease in heterozygous mice carrying Pkhd1 gene trap or exon deletions. To determine whether heterozygosity for a smaller Pkhd1 defect can trigger cystic renal disease in mice, we generated and characterized mice with the predicted truncating Pkhd1C642* mutation in a region corresponding to the middle of exon 20 cluster of five truncating human mutations (between PKHD1G617fs and PKHD1G644*). Mouse heterozygotes or homozygotes for the Pkhd1C642* mutation did not have noticeable liver or renal abnormalities on magnetic resonance images during their first weeks of life. However, when aged to ~1.5 yr, the Pkhd1C642* heterozygotes developed prominent cystic liver changes; tissue analyses revealed biliary cysts and increased number of bile ducts without signs of congenital hepatic fibrosis-like portal field inflammation and fibrosis that was seen in Pkhd1C642* homozygotes. Interestingly, aged female Pkhd1C642* heterozygotes, as well as homozygotes, developed radiographic changes resembling MSK. However, these changes correspond to proximal tubule ectasia, not an MSK-associated collecting duct ectasia. In summary, by demonstrating that cystic liver and kidney abnormalities are triggered by heterozygosity for the Pkhd1C642* mutation, we provide important validation for relevant human association studies. Together, these investigations indicate that PKHD1 mutation heterozygosity (predicted frequency 1 in 70 individuals) is an important underlying cause of cystic liver disorders and MSK-like manifestations in a human population.

Spontaneous calcification process in primary renal cells from a medullary sponge kidney patient harbouring a GDNF mutation.

Medullary nephrocalcinosis is a hallmark of medullary sponge kidney (MSK). We had the opportunity to study a spontaneous calcification process in vitro by utilizing the renal cells of a patient with MSK who was heterozygous for the c.-27 + 18G>A variant in the GDNF gene encoding glial cell-derived neurotrophic factor. The cells were obtained by collagenase digestion of papillary tissues from the MSK patient and from two patients who had no MSK or nephrocalcinosis. These cells were typed by immunocytochemistry, and the presence of mineral deposits was studied using von Kossa staining, scanning electron microscopy analysis and an ALP assay. Osteoblastic lineage markers were studied using immunocytochemistry and RT-PCR. Staminality markers were also analysed using flow cytometry, magnetic cell separation technology, immunocytochemistry and RT-PCR. Starting from p2, MSK and control cells formed nodules with a behaviour similar to that of calcifying pericytes; however, Ca2PO4 was only found in the MSK cultures. The MSK cells had morphologies and immunophenotypes resembling those of pericytes or stromal stem cells and were positive for vimentin, ZO1, αSMA and CD146. In addition, the MSK cells expressed osteocalcin and osteonectin, indicating an osteoblast-like phenotype. In contrast to the control cells, GDNF was down-regulated in the MSK cells. Stable GDNF knockdown was established in the HK2 cell line and was found to promote Ca2PO4 deposition when the cells were incubated with calcifying medium by regulating the osteonectin/osteopontin ratio in favour of osteonectin. Our data indicate that the human papilla may be a perivascular niche in which pericyte/stromal-like cells can undergo osteogenic differentiation under particular conditions and suggest that GDNF down-regulation may have influenced the observed phenomenon.

Biopsy proven medullary sponge kidney: clinical findings, histopathology, and role of osteogenesis in stone and plaque formation.

Medullary sponge kidney (MSK) is associated with recurrent stone formation, but the clinical phenotype is unclear because patients with other disorders may be incorrectly labeled MSK. We studied 12 patients with histologic findings pathognomonic of MSK. All patients had an endoscopically recognizable pattern of papillary malformation, which may be segmental or diffuse. Affected papillae are enlarged and billowy, due to markedly enlarged inner medullary collecting ducts (IMCD), which contain small, mobile ductal stones. Patients had frequent dilation of Bellini ducts, with occasional mineral plugs. Stones may form over white (Randall's) plaque, but most renal pelvic stones are not attached, and have a similar morphology as ductal stones, which are a mixture of calcium oxalate and apatite. Patients had no abnormalities of urinary acidification or acid excretion; the most frequent metabolic abnormality was idiopathic hypercalciuria. Although both Runx2 and Osterix are expressed in papillae of MSK patients, no mineral deposition was seen at the sites of gene expression, arguing against a role of these genes in this process. Similar studies in idiopathic calcium stone formers showed no expression of these genes at sites of Randall's plaque. The most likely mechanism for stone formation in MSK appears to be crystallization due to urinary stasis in dilated IMCD with subsequent passage of ductal stones into the renal pelvis where they may serve as nuclei for stone formation.

Nephrolithiasis in medullary sponge kidney: evaluation of clinical and metabolic features.

OBJECTIVE: Medullary sponge kidney (MSK) is a disorder characterized by tubular dilation of renal collecting ducts and cystic dilation of medullary pyramids that has been associated with stone disease. The significance of nephrolithiasis and the mechanisms by which it occurs are incompletely understood. We describe clinical and metabolic features of nephrolithiasis in a cohort of patients with MSK. METHODS: Records were reviewed of 56 patients, all with radiographic diagnosis of medullary sponge kidney and data collected pertaining to presentation, stone events and recurrences, stone composition, and metabolic profile to perform a descriptive study with median 3.7 years follow-up. RESULTS: Nephrolithiasis was confirmed radiographically in 39/56 patients (69.6%). No patient without evidence of nephrolithiasis developed a stone event, whereas 13/39 (33%) of those with nephrolithiasis developed a recurrent stone event. Stones were composed of calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate apatite, and uric acid. Metabolic profile was obtained for 26 of 39 (67%) stone-forming patients demonstrating abnormalities in 22/26 (84.6%). These included hypercalciuria, 58% (15/26); low urine volume, 35% (9/26); hyperuricosuria, 27% (7/26); hypocitraturia, 19% (5/26); elevated urine sodium, 15% (4/26); and hyperoxaluria, 12% (3/26). CONCLUSION: Many patients with MSK have no evidence of nephrolithiasis. Among those who do, recurrence is common, and metabolic profile and composition are varied as in the general stone-forming population.

Nephrolithiasis in medullary sponge kidney.

Seventy-one patients with documented Medullary Sponge Kidney (MSK) and nephrolithiasis underwent complete metabolic evaluation. These patients constituted 7.3% of our calcium stone-forming population Metabolic anomalies (hypercalciuria, hyperoxaluria, hypocitraturia and hyperuricosuria) were observed in 82% of patients. No patient was hypercalcemic and none had hyperparathyroidism. Thus the patients with medullary sponge kidney and renal stones had the same spectrum of metabolic anomalies as the overall population of idiopathic stone formers. Although these patients may have anatomic anomalies which determine stasis of urine and infection causing stone formation, they should be evaluated and treated appropiately for any metabolic defect.

Identification of GDNF gene sequence variations in patients with medullary sponge kidney disease.

BACKGROUND AND OBJECTIVES: Medullary sponge kidney (MSK) is a rare nephropathy characterized by cystic anomalies of precalyceal ducts, nephrocalcinosis, renal stones, and tubule dysfunctions. Its association with various malformations and cases of familial aggregation supports the conviction that genetic factors are involved, but no genetic studies have been conducted to date. It is hypothesized that MSK is due to a disruption at the "ureteric bud/metanephric blastema" interface caused by critical developmental genes functioning abnormally. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Fifty-five apparently sporadic MSK patients were analyzed by direct DNA sequencing of all exons and exon-intron boundaries of glial cell-derived neurotrophic factor (GDNF) gene and rearranged during transfection (RET) gene, which have a leading role in renal development. RESULTS: Two novel variants were found in heterozygosity in the MSK case population: GDNF{ENST00000344622}:c.-45G>C and c.-27+18G>A in a putative binding domain for paired-box 2 transcription factor. As a whole, eight patients showed these variations: four patients carried the c.[-45G>C; -27+18G>A] complex allele, and the others had the c.-27+18G>A alone. A case-control study revealed that these two alleles were significantly associated with MSK. Five of the eight cases were found to be familial, and the allele variants cosegregated with the disease in a seemingly dominant pattern of inheritance. Patients revealed no mutations in the RET gene. CONCLUSIONS: This is the first report identifying GDNF gene sequence variations in patients with MSK and suggesting a role for this gene in the pathogenesis of some cases of the disease.

Contributory metabolic factors in the development of nephrolithiasis in patients with medullary sponge kidney.

Whether specific metabolic abnormalities are related to nephrolithiasis in patients with medullary sponge kidney (MSK) remains a debated issue. The purpose of this study is to determine metabolic disorders in patients with MSK and nephrolithiasis compared with idiopathic calcium-stone-forming patients. One hundred eighty-four patients with recurrent calcium-stone formations were investigated with regard to metabolic abnormalities. Of these, 22 patients (11.9%; 13 men, 9 women) showed MSK by radiological examination. MSK was defined as a kidney that presented at least three linear or round papillary opacities in the affected papilla on urography. Multiple stones (more than five) existed in both kidneys in all patients with MSK. The remaining 162 patients (109 men, 53 women) were idiopathic calcium-stone formers. Frequencies of low urine volume (urine < 1,500 mL/24 h) and hyperoxaluria (oxalate > 40 mg/24 h) were similar between the groups. Hypercalciuria (men, calcium > 300 mg/24 h; women, calcium of 250 mg/24 h) was found less frequently in the MSK group. The frequency of hypocitraturia (citrate < 300 mg/24 h) was significantly greater in the MSK group than the idiopathic group (77.3% versus 33.9%, respectively). Mean 24-hour urinary excretions of calcium, citrate, uric acid, and magnesium were significantly less in the MSK group. No differences were found in serum calcium, phosphate, and parathyroid hormone levels between the groups. Low urinary excretions of citrate and magnesium are the most typical metabolic disorders that distinguish MSK stone patients from idiopathic calcium-stone-forming patients. In addition to such anatomic abnormalities as ectatic collecting ducts, low levels of urinary inhibitors of stones seem to contribute to the pathogenesis of nephrolithiasis in patients with MSK.

[Clinical studies on medullary sponge kidney evaluated from urolithiasis].

Thirty eight patients with medullary sponge kidney (MSK) were detected (4.3%) in 881 patients with urolithiasis diagnosed by drip infusion pyelography in 12 years from January 1974 to December 1985. Those with MSK were studied clinically and as to metabolism of urolithiasis. The results obtained were as follows: 1) Age distribution of the patients with MSK was the same as that of general stone formers. 2) Hematuria was observed in 20 patients (52.6%) and pyuria in 7, in whom 4 were positive by urine culture (E. coli in 3 and P. mirabilis in 1) and 2 of them had infective stones. 3) Renal function of the patients examined by PSP test (20 patients) and creatinine clearance test (21 patients) was normal in all of the patients but three with ureteral caliculi. Concentration tests performed by Fishberg method (12 patients) were disturbed in half of them. 4) Affected lesions wer detected at more than three pyramides in each kidney and the bilaterals were found in 32 patients (84.2%) and at less than two pyramides in each kidney and the unilateral or the bilaterals were shown in the other 6. 5) When urinary levels of calcium, phosphate, uric acid and citrate using 24 hours urine were compared with 37 patients with MSK and 100 general stone formers, there was no difference in hypercalciuria and hyperuricosuria accounting for the frequency of the patients with MSK and the general stone formers, but there was a tendency of increased frequency about hyperphosphaturia and hypocitraturia in the patients with MSK.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic evaluation of nephrolithiasis in patients with medullary sponge kidney.

Seventeen patients with documented medullary sponge kidney and nephrolithiasis underwent metabolic evaluation. These patients constituted 3.6% of our stone-forming population. Fifteen (88%) of 17 were hypercalciuric. The most common abnormality was absorptive hypercalciuria, occurring in 59%. Only three patients (18%) had renal hypercalciuria. None of the patients had primary hyperparathyroidism. Hyperuricosuria occurred together with hypercalciuria in five patients. In two patients, the precise cause of hypercalciuria could not be determined, and in another two patients, no metabolic abnormality could be detected. Thus, the patients with medullary sponge kidney and renal stones had the same spectrum of metabolic abnormalities as the overall population of stone formers. While these patients may theoretically have a greater anatomic propensity to form stones because of their anatomic abnormality, they should be evaluated and treated appropriately for any metabolic defect.

Medullary sponge kidney: abnormalities of renal tubular and glomerular function, and their relationship to clinical features.

This study confirms that medullary sponge kidney (MSK) has a good prognosis, but there is a considerable morbidity in patients with renal calcification; they suffer renal colic, ureteric obstruction, and frequently need operation. There is a high incidence of urinary infection in women. On follow-up, glomerular function is well maintained, although careful testing shows a mild depression of glomerular filtration rate in at least 40%. Proximal tubular function is normal, but abnormalities of distal tubular function are often seen: acidification defects occur in 24% and are associated with nephrocalcinosis, poor urine concentrating ability, and diminished glomerular function. Urine concentration defects occur in 73% and are probably secondary to nephrocalcinosis. Hypercalciuria was present in 19% and was not related to other defects.