CJASN ePress. Published on August 8, 2007 as doi: 10.2215/CJN.00900207

Hypothesis: Dent Disease Is an Underrecognized Cause of Focal

Lawrence Copelovitch,* Martin A. Nash,† and Bernard S. Kaplan* *Department of Pediatrics, Division of , The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania; and †Department of Pediatrics, Division of Nephrology, Columbia University Medical Center, New York, New York

Background and Objectives: Dent disease is a hereditary form of progressive renal failure characterized by and proximal tubular dysfunction. The clinical presentation is often insidious with the majority of patients remaining asymptomatic throughout childhood. Despite the seemingly mild, early course, more than 20% of 32 asymptomatic patients in one study had biopsy evidence of focal glomerulosclerosis. Furthermore, end-stage renal disease often occurs in men in early to middle adulthood. Design, Setting, Participants, & Measurements: This article describes two male patients who presented with asymptomatic proteinuria and were found to have focal glomerulosclerosis. Despite the absence of on renal ultrasound, the diagnosis of Dent disease was considered because of unexplained proteinuria. Subsequent history revealed renal calculi in each maternal family. Results: The clinical diagnosis of Dent disease was established by intermittent hypercalciuria and low molecular weight proteinuria and confirmed through mutational analysis. Conclusions: It is hypothesized that a diagnosis of Dent disease may be unrecognized in patients with unexplained proteinuria and idiopathic focal glomerulosclerosis. Clin J Am Soc Nephrol 2: 914-918, 2007. doi: 10.2215/CJN.00900207

ocal segmental glomerulosclerosis (FSGS) is an impor- lar barrier. Observations that support the hypothesis that there tant cause of proteinuria and in is a circulating factor include the response of some cases of F pediatric patients and is now the most frequent cause of FSGS to medications that suppress lymphocyte function, the nephrotic syndrome in adults (1). There is also substantial risk recurrence of nephrotic syndrome after renal transplantation, for progression to ESRD. The histopathologic findings in FSGS and the injection of serum from patients with FSGS into healthy can be secondary to systemic conditions that include chronic rats with a resultant nephrotic syndrome (2). Despite numerous hypoxemia, reduced nephron mass, HIV infection, and obesity. attempts, the isolation of these factors has remained elusive. Similar histopathologic findings are seen in idiopathic (pri- In addition to the podocyte-related and immunologic-medi- mary) FSGS. These nonspecific histopathologic findings are the ated causes of focal sclerosis, several tubulopathies (Dent dis- reaction of the glomerulus to many types of injury and do not ease, , Bartter syndrome, and inherited dis- represent a single disease. tal ) have been associated with focal In the past 10 yr, studies on the podocyte and its related glomerulosclerosis (3–9). This further suggests that the entity proteins have added to our understanding of the inherited known as focal glomerulosclerosis is not a singular diagnosis forms of idiopathic FSGS. Mutations in the Podocin gene, ␣-Ac- but rather a final common pathway resulting from injury that tinin 4 gene, and CD2AP gene cause inherited FSGS (1). These occurs at multiple areas of the nephron. Although systemic proteins are located in the podocyte foot process and have a conditions, reduced nephron mass, inherited podocytopathies, critical role in podocyte function, structure, and interactions and immune dysregulation all have been well established as with the extracellular lipid rafts. Despite these significant ad- causes of focal sclerosis, we wish to add the primary tubulopa- vances, the cause of the majority of cases of FSGS remains thies to the growing list of causes. unknown. In this case report, we review the literature and report two Primary FSGS may also result from undefined circulating children who had Dent disease and developed significant pro- factors or cytokines that alter the permeability of the glomeru- teinuria and biopsy-proven focal glomerulosclerosis. We be- lieve that primary tubulopathies, in particular Dent disease, should not be overlooked in the differential diagnosis when

Received February 21, 2007. Accepted May 7, 2007. considering a patient with idiopathic focal glomerulosclerosis.

Published online ahead of print. Publication date available at www.cjasn.org. Case Reports Address correspondence to: Dr. Lawrence Copelovitch, The Children’s Hospital Patient 1 of Philadelphia, Division of Nephrology, Department of Pediatrics, 34th Street & Civic Boulevard, Philadelphia, PA 19104. Phone: 215-590-2449; Fax: 215-590-3705; A 12-yr-old boy was referred for evaluation of asymptomatic E-mail: [email protected] proteinuria detected on a routine sports physical examination.

Copyright © 2007 by the American Society of Nephrology ISSN: 1555-9041/205–0914 Clin J Am Soc Nephrol 2: 914-918, 2007 Dent Disease as Cause of Focal Glomerulosclerosis 915

During the preceding two years, he was noted to have ortho- disease was considered. The initial spot urine calcium/creati- static proteinuria with negative tests on first-morning speci- nine ratio was 0.8 (normal Ͻ0.2), and the ␤2-microglobulin mens. The proteinuria was subsequently also present in first- excretion was 32,203 ␮g/L (normal 1 to 160 ␮g/L). During the morning samples. The patient did not have edema, gross past year, the urinary calcium excretion has only been intermit- , or recent illnesses. Pregnancy and birth were nor- tently elevated. mal and term; however, ABO incompatibility required blood Analysis of the CLCN5 gene showed a duplication of the “A” transfusions. nucleotide at the 523rd base of the sixth exon (523dupA). The Family History. A maternal grandfather had a history of resulting frameshift mutation in the 175th codon (Thr175fsX8) renal calculi; he died at 67 yr from glomerulosclerosis, hyper- causes a premature stop codon sequence eight residues down- tension, and end-stage renal failure that required dialysis. The stream from the duplication. This analysis was performed by patient’s father received a diagnosis of nerve deafness at 9 yr GeneDx (Gaithersburg, MD). and wears hearing aids. His mother was diagnosed with a bifurcated uterus and an incompetent cervix. Patient 2 Physical Examination. The boy’s height was 138.3 cm (fifth A 9-yr-old boy was referred for evaluation of asymptomatic to 10th percentile), his weight was 35 kg (10th to 25th percen- proteinuria. At 1 yr of age, he had intermittent fevers and tile), and his BP was 90/50 mmHg. There were no dysmorphic hepatosplenomegaly. An extensive metabolic and hematologic features. He had normal nails and patellae, normal cardiac evaluation for a cause of the hepatosplenomegaly was negative. examination, no rashes, no arthritis, and no periorbital or pedal The fevers resolved, and during the next 8 yr, he remained edema. asymptomatic. However, the slightly enlarged spleen and liver Laboratory Studies. Initial serum concentrations all were persisted. At the age of 4 yr, he was evaluated for urinary normal: Sodium 137 mEq/L, potassium 3.8 mEq/L, chloride frequency and dysuria. A urine dipstick showed microscopic 102 mEq/L, carbon dioxide 25 mEq/L, calcium 9.5 mg/dl, hematuria and 300 mg/dl protein. Subsequent studies revealed phosphorous 3.8 mg/dl, albumin 4.7 g/dl, total cholesterol 201 a normal renal ultrasound, normal serum electrolytes, normal mg/dl, creatinine 1.0 mg/dl, C3 107 mg/dl, and C4 38 mg/dl. serum creatinine, normal serum albumin, 1321 mg of protein in Initial urine protein/creatinine ratio was 1.6 mg/mg. Twenty- a 24-h urine collection, and persistent proteinuria in a first- four-hour protein excretion was 1283 mg/24 h. Creatinine morning sample. At the age of 7 yr, his serum creatinine began clearance estimated by the Schwartz formula was 95 ml/min to increase to 1.0 mg/dl and, a was performed. per 1.73 m2. During the subsequent 5 mo, the 24-h protein Five glomeruli were available for analysis; two were globally excretion increased to 1750 mg/24 h. An initial urinalysis dur- sclerotic and three were normal. We first saw the patient for a ing his initial clinic visit showed trace protein, trace blood, no second opinion 2 mo after his initial renal biopsy. At that time, glucose, and no casts. In retrospect, the finding on protein he did not have edema, gross hematuria, or recent illnesses. We electrophoresis that very little of the total urine protein was elected to repeat a kidney biopsy. albumin and that most of the protein was globulin explained Family History. Both maternal grandparents had a history the discrepancy between the finding on standard urinalysis dip of renal calculi. A maternal aunt had a history of hearing loss. sticks that detect only albumin and the measurement of total His mother has anticardiolipin antibodies and has had two protein. miscarriages. There is no family history of . Imaging Studies. A renal ultrasound showed normal- Physical Examination. The boy’s height was 129.7 cm sized kidneys for age and height. The right measured 7.3 cm, (25th percentile), his weight was 27.6 kg (50th percentile), and and the left measured 8.0 cm. There was normal echotexture his BP was 95/62 mmHg. There were no dysmorphic features. and no evidence of a calculus or nephrocalcinosis. He had normal nails and patellae; normal cardiac examination; Renal Biopsy. Thirty-seven glomeruli were present for and no rashes, arthritis, or peripheral edema. The abdomen was light microscopy analysis. There were areas of focal global soft and nontender. The liver was not enlarged, and the spleen glomerulosclerosis (FGGS). Twenty-five percent (nine of 37) of was palpable two finger breadths below the costal margin. the glomeruli were globally sclerotic. Perihilar hyalinosis was Laboratory Studies. Initial serum concentrations all were seen at the vascular pole of one glomerulus. Uninvolved glo- normal: Sodium 141 mEq/L, potassium 3.9 mEq/L, chloride meruli were slightly enlarged with minimal segmental in- 105 mEq/L, carbon dioxide 25 mEq/L, calcium 9.6 mg/dl, creases in mesangial cells. There was slight tubular atrophy and phosphorous 4.4 mg/dl, albumin 4.6 g/dl, and total cholesterol interstitial fibrosis involving Ͻ5% of the cortex. Direct immu- 169 mg/dl. The serum creatinine concentration was 0.9 mg/dl. nofluorescent microscopy of the nonsclerotic glomeruli was Creatinine clearance as estimated by the Schwartz formula was minimally positive for IgM in the mesangium of several glo- 79 ml/min per 1.73 m2. meruli. Staining for IgG, IgA, C3, and C1q was negative. Elec- Imaging Studies. A renal ultrasound showed normal- tron microscopy revealed no electron-dense deposits and a sized kidneys for age and height. The right measured 8.0 cm, normal glomerular basement membrane. The visceral epithelial and the left measured 7.6 cm. There was minimal pelviectasis cells had effacement of 10% of the foot processes. bilaterally, normal echotexture, and no evidence of calculi or Course. Two months after treatment with enalapril, there nephrocalcinosis. was moderate reduction in protein excretion to 880 mg/24 h. Renal Biopsy. Six glomeruli were evaluated by light mi- The family obtained a second opinion, and a diagnosis of Dent croscopy. There were areas of focal global and segmental glo- 916 Clinical Journal of the American Society of Nephrology Clin J Am Soc Nephrol 2: 914-918, 2007 merulosclerosis. Two of the glomeruli were globally sclerotic, acidosis (9). ESRD can occur between the ages of 25 and 50 yr two to three glomeruli were segmentally sclerosed in some in patients with Dent disease (16). However, data on the long- levels and globally scleroses in others, and one glomerulus was term outcomes of patients with Gitelman and Bartter syn- completely normal. Periglomerular fibrosis was seen around dromes is scanty but important in regard to our hypothesis. one glomerulus. There was patchy, mild interstitial chronic Eighteen patients with Bartter syndrome in the North Ameri- inflammation and proteinaceous casts in some tubules. Other can Pediatric Renal Cooperative Study database had renal fail- tubules contained granular calcifications. The material exam- ure. Unfortunately, the specific causes of the renal failure were ined for immunofluorescence did not contain any glomeruli. not available (7). ESRD has also been reported in Gitelman Electron microscopy revealed no electron-dense deposits and a syndrome (17,18), but histologic findings were not included in uniform capillary basement membrane thickness with some the reports. wrinkling in the perimesangial region. The visceral epithelial Bouisso et al. (19) described nine children with proximal cells had variable effacement of several of the foot processes. tubular dysfunction noted 2 to 25 mo after diagnosis of steroid- Course. The family deferred starting a trial of enalapril. resistant nephrotic syndrome. There were combinations of glu- During the past 5 yr, the creatinine has increased to 1.3 mg/dl. cosuria, , metabolic acidosis, hypophosphatemia, Subsequent to the renal biopsy, a diagnosis of Dent disease was and hypouricemia (19). McVicar et al. (20) reported five cases of considered. The spot urine calcium/creatinine ratio was 0.07 childhood nephrotic syndrome associated with renal glycosuria (normal Ͻ0.2), the ␤2-microglobulin excretion was 52,700 ␮g/L and other tubular defects and suggested that these were early (normal 1 to 160 ␮g/L), and there was a generalized aminoaci- manifestations of FSGS. The proximal tubular defects were duria. noted within the first 3 to 22 mo of diagnosis and at a time Analysis of the CLCN5 gene showed a duplication of 3 bp at when the level of renal function was either normal or slightly the 744th bp in the seventh exon (c744_746dupACG). The re- depressed (GFR 56 to 90 ml/min per 1.73 m2). All of the sulting insertion of an alanine residue at codon 249 is thought children had renal glycosuria as the initial tubular defect, and to disrupt a highly conserved series of five alanine residues, several also developed aminoaciduria, bicarbonaturia, and thereby disrupting a D5 transmembrane domain. This analysis phosphaturia. Two of the five patients had near-normal renal was performed by GeneDx (Gaithersburg, MD). function at the time of their initial tubular dysfunction and no evidence of FSGS or interstitial pathology in the initial biopsy Discussion specimen. These findings could suggest that a proximal tubular Proximal tubular dysfunction is more common when the defect preceded the onset of the glomerulosclerosis. nephrotic syndrome is associated with FSGS than with mini- Dent disease is an X-linked renal tubular disorder that is mal-change nephrotic syndrome (10,11). Furthermore, patients characterized by low molecular weight proteinuria, hypercal- with minimal-change nephrotic syndrome rarely have tubulo- ciuria, nephrolithiasis, and progressive renal failure. Glucos- interstitial involvement, whereas those with FSGS often have uria, aminoaciduria, metabolic acidosis, and hypophos- tubulointerstitial infiltration and fibrosis (12). Most investiga- phatemia can also occur. X-linked recessive nephrolithiasis, tors have assumed that the nonselective proteinuria in FSGS X-linked recessive hypophosphatemic rickets, and the idio- causes proximal tubular cell injury with the resultant tubulo- pathic low molecular weight proteinuria of Japanese children interstitial damage and scarring. Valles et al. (13) evaluated all are caused by the mutations in the same voltage-gated urinary ␤2-microglobulin and N-acetyl-␤-d-glucosaminidase CLCN5 that result in the Dent disease. They levels (low molecular weight proteins) in 11 patients with FSGS are now collectively referred to as Dent disease on the basis of and found no correlation between the degree of interstitial phenotypic similarities and common genetic cause (21). In a fibrosis and low molecular weight proteinuria. Consistent with study of 32 children who underwent renal biopsy, Murakami et these observations, we challenge the universality of the ac- al. (4) found that 22% of asymptomatic Japanese children with cepted chronology of events that suggests that nonselective idiopathic low molecular weight proteinuria had FGGS. On the proteinuria in focal sclerosis causes tubulointerstitial damage basis of the relatively high percentage of patients who had Dent and fibrosis that causes tubular dysfunction. We propose that disease and developed focal glomerulosclerosis in the report of in some cases of FSGS, the tubular dysfunction or damage is the Murakami et al. (4) and the frequency of early proximal tubular primary renal insult and that the glomerulosclerosis may be a dysfunction in two case series (19,20), we suggest that Dent secondary epiphenomenon. disease may not be recognized when it presents as idiopathic In several animal models, high-grade nonselective protein- focal glomerulosclerosis and perhaps steroid-resistant ne- uria results in proximal tubular swelling, toxicity, and eventual phrotic syndrome. This could result in unnecessary treatment tubulointerstitial inflammation (14,15). It is interesting that with high dosages of corticosteroids and immunosuppressive none of these models has demonstrated that the end result of agents. these tubular insults is wasting of glucose, amino acids, or Focal sclerotic lesions of glomeruli can be differentiated into electrolytes. The inherited tubulopathies provide a clear exam- two types: FSGS, involving only part of the glomerular tuft, and ple of renal diseases in which the initial damage is tubular but FGGS, with complete obsolescence in a variable number of the end result is FSGS. For example, there are a few reports of glomeruli. FGGS can be seen as part of the normal involution of FSGS associated with Dent disease (3–5), Gitelman syndrome nephrons. The number of such glomeruli is Ͻ10% in 95% of the (6,7), Bartter syndrome (8), and inherited distal renal tubular population under 40 yr of age (22,23). In infants, the presence of Clin J Am Soc Nephrol 2: 914-918, 2007 Dent Disease as Cause of Focal Glomerulosclerosis 917 an occasional global sclerotic glomerulus may represent an 2. Benchimol C: Focal segmental glomerulosclerosis: Patho- error in nephron formation. In pathologic conditions, such as genesis and treatment. Curr Opin Pediatr 15: 171–180, 2003 idiopathic nephrotic syndrome, both focal segmental and 3. Langlois V, Chantale B, Scheinman SJ, Thakker RV, Cox JP, global lesions may be seen as part of the progression of focal Goodyer PR: Clinical features of X-linked nephrolithiasis sclerosis to sclerosis of the entire glomerulus, particularly when in childhood. Pediatr Nephrol 12: 625–629, 1998 4. Murakami T, Kawakami H: The clinical significance of associated with tubular atrophy. It has been suggested that asymptomatic low molecular weight proteinuria detected children with the nephrotic syndrome and only FGGS without on routine screening of children in Japan: A survey of 53 tubular atrophy form a subgroup with a more favorable prog- patients. Clin Nephrol 33: 12–19, 1990 nosis, not unlike that of children with minimal-change disease 5. Scheinman SJ: X-linked hypercalciuric nephrolithiasis: (22,23). Clinical syndromes and chloride channel mutations. Kid- Patients with Dent disease and glomerular abnormalities on ney Int 57: 240–249, 1998 renal biopsy usually have FGGS. The tubulointerstitial findings 6. Bulucu F, Vural A, Yenicesu M, Caglar K: Association of are variable and range from normal to interstitial fibrosis or Gitelman’s syndrome and focal glomerulosclerosis. tubular atrophy (3,4). Because of the irregularity of the sclerotic Nephron 79: 244, 1998 process, the presence of one or more segmentally sclerotic 7. Hanevold C, Mian A, Dalton R: C1q nephropathy in asso- lesions can occur. Whether FGGS is invariably a separate entity ciation with Gitelman syndrome: A case report. Pediatr from FSGS or is part of a continuum has yet to be fully deter- Nephrol 21: 1904–1908, 2006 8. Su IH, Frank R, Gauthier BG, Valderrama E, Simon DB, mined. Frymoyer et al. (16) described at least one patient who Lifton RP, Tracthman H: Bartter syndrome and focal seg- had Dent disease and had renal biopsy findings that showed mental glomerulosclerosis: A possible link between two that 25% of the glomeruli had “partial-to-global sclerosis.” One diseases. Pediatr Nephrol 14: 970–972, 2000 helpful diagnostic point is that the electron microscopy find- 9. Balgoun RA, Adams ND, Palmisano J, Yamase H, ings in Dent disease show minimal effacement of the epithelial Chughtai I, Kaplan AA: Focal segmental glomerulosclero- foot processes, in contrast to FSGS with nephrotic syndrome. sis, proteinuria and nephrocalcinosis associated with renal We believe that given the lack of convincing evidence in the tubular acidosis. Nephrol Dial Transplant 17: 308–310, 2002 literature, the diagnosis of Dent disease should be considered in 10. Sesso R, Santos AP, Nishida SK, Klag MJ, Carvalhaes JT, patients with both FGGS and FSGS. Ajzen H, Ramos OL, Pereira AB: Predicition of steroid Focal glomerulosclerosis is a nonspecific histologic finding responsiveness in idiopathic nephrotic syndrome using that seems to be the reaction of the glomerulus to a variety of urinary retinol-binding protein and beta2-microglobulin. Ann Intern Med 116: 905–909, 1992 renal insults. Various tubulopathies have been associated with 11. Shah V, Taylor GM, Dillon SC: Diagnostic value of urinary focal glomerulosclerosis. Dent disease is potentially the most retinol-binding protein in childhood nephrotic syndrome. important of these causes because it often goes unrecognized as Pediatr Nephrol 12: 643–647, 1998 a result of the mild initial clinical features, the absence of overt 12. Ichikawa I, Fogo A: Focal segmental glomerulosclerosis. serum electrolyte abnormalities, and the low incidence (5 to Pediatr Nephrol 10: 374–391, 1996 10%) of glucosuria on routine urinalysis (4). Furthermore, as 13. Valles P, Peralta M, Carrizo L, Martin L, Principi I, Gonza- was noted in our patients, even when the diagnosis is consid- lez A, Manucha W: Follow-up of steroid-resistant ne- ered, hypercalciuria may not be a constant finding. For reasons phrotic syndrome: Tubular proteinuria and enzymuria. that are still unclear, Dent disease may result in ESRD between Pediatr Nephrol 15: 252–258, 2000 the ages of 25 and 50 yr. We recommend early consideration of 14. Eddy AA: Experimental insights into the tubulointerstitial the diagnosis of Dent disease in all cases of unexplained pro- disease accompanying primary glomerular lesions. JAm Soc Nephrol teinuria and idiopathic focal sclerosis. This can be done initially 5: 1273–1287, 1994 15. Remuzzi G, Ruggenenti P, Benigni A: Understanding the by screening the urine for excretion of calcium and ␤2-micro- nature of renal disease progression. Kidney Int 51: 2–15, globulin. An accurate diagnosis could prevent needless expo- 1997 sure to potentially hazardous cytotoxic medications in some 16. Frymoyer PA, Scheinman SJ, Dunham PB, Jones DB, Hue- patients. Furthermore, Cebotaru et al. (24) fed high-citrate diets ber P, Schroeder ET: X-linked recessive nephrolithiasis to ClC-5 knockout mice (a murine model of Dent disease) and with renal failure. N Engl J Med 325: 681–686, 1991 significantly delayed progression of renal disease. If these find- 17. Bonfante L, Davis PA, Spinello M, Antonello A, D’Angelo ings translate to human patients, then making the appropriate A, Semplicini A, Calo L: Chronic renal failure, end-stage diagnosis could be important. renal disease, and peritoneal dialysis in Gitelman’s syn- drome. Am J Kidney Dis 38: 165–168, 2001 18. Calo LA, Marchini F, Davis PA, Rigotti P, Pagnin E, Sem- Disclosures plicini A: Kidney transplant in Gitelman’s syndrome. Re- None. port of the first case. J Nephrol 16: 144–147, 2003 19. Buissou F, Barthe P, Pierragi MT: Severe idiopathic ne- phrotic syndrome with tubular dysfunction (report of nine References cases). Clin Nephrol 14: 135–141, 1980 1. Daskalakis N, Winn MP: Focal and segmental glomerulo- 20. McVicar M, Exeni R, Susin M: Nephrotic syndrome and sclerosis: Varying biologic mechanisms underlie a final multiple tubular defects in children: An early sign of focal histologic end point. Semin Nephrol 26: 89–94, 2005 segmental glomerulosclerosis. J Pediatr 97: 918–922, 1980 918 Clinical Journal of the American Society of Nephrology Clin J Am Soc Nephrol 2: 914-918, 2007

21. Igarashi T, Inatomi J, Ohara T, Kuwaha T, Shimadzu M, 23. Nash MA, Greifer I, Olbing H, Bernstein J, Bennett B, Thakker RV: Clinical and genetic studies of CLCN5 muta- Spitzer A: The significance of focal sclerotic lesions of tions in Japanese families with Dent’s disease. Kidney Int glomeruli in children. J Pediatr 88: 806–813, 1976 28: 520–527, 2000 24. Cebotaru V, Kaul S, Devuyst O, Cai H, Racusen L, Guggino 22. Querfeld U, Waldherr R, Scharer K: The significance of WB, Guggino SE: High citrate diet delays progression of focal global sclerosis in idiopathic nephrotic syndrome. renal insufficiency in the ClC-5 knockout mouse model of Acta Paediatr Scand 74: 913–919, 1985 Dent’s disease. Kidney Int 68: 642–652, 2005