Nodular Regenerative Hyperplasia and Severe Portal Hypertension in Cystinosis

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1 CLINICAL GASTROENTEROLOGY AND HEPATOLOGY 2006;4: Nodular Regenerative Hyperplasia and Severe Portal Hypertension in Cystinosis KEVIN O BRIEN,*, NADEEM HUSSAIN, BRADLEY A. WARADY, DAVID E. KLEINER, ROBERT KLETA,*, ISA BERNARDINI,* THEO HELLER, and WILLIAM A. GAHL* *Section on Human Biochemical Genetics, Medical Genetics Branch, National Human Genome Research Institute, Intramural Office of Rare Diseases, Office of the Director, Digestive Diseases Branch, National Institute of Digestive Diseases and Kidney Disorders, Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland; and the Section of Nephrology, The Children s Mercy Hospital, Kansas City, Missouri Background & Aims: Cystinosis is a rare autosomalrecessive disorder characterized by the intralysosomal accumulation of cystine, which is responsible for widespread tissue destruction. Liver biopsy specimens of patients with cystinosis show cystine crystal formation in Kupffer cells. However, significant liver disease and portal hypertension is not a common complication of cystinosis. We report the case histories of 2 young men with poorly treated nephropathic cystinosis who developed noncirrhotic portal hypertension with evidence of nodular regenerative hyperplasia (NRH). Methods: Liver biopsy examinations, upper and lower endoscopy with biopsy examination, imaging studies, venous pressure measurements, and laboratory investigations were used to evaluate the causes of the liver disease and portal hypertension. Results: Histologic examination of liver biopsy specimens from both patients showed changes characteristic of NRH with portal hypertension documented by measurement of pressure gradients. In addition, endoscopy in the first patient showed varices and portal hypertensive gastropathy. Conclusions: NRH was confirmed by histologic examination of the liver in both patients and is the likely cause of their portal hypertension. NRH may represent a rare, late complication of cystinosis, although the mechanism remains undefined. Cystinosis is an autosomal-recessive lysosomal storage disease with an estimated incidence of 1 in ,000 live births. 1,2 CTNS, the gene responsible for cystinosis, maps to chromosome 17p13 3 and encodes a lysosomal membrane transport protein named cystinosin. 4 In nephropathic cystinosis, a defect in cystinosin dramatically diminishes egress of cystine from lysosomes, 5,6 resulting in intralysosomal cystine accumulation and crystal formation in most organ systems. 1,2,7 Cystinosis is diagnosed by finding an increased leukocyte cystine level, generally more than 3 nmol half-cystine/mg protein (normal,.2). 1,2 In the natural history of nephropathic cystinosis, the chronic accumulation of intracellular cystine causes renal tubular Fanconi syndrome in infancy, hypothyroidism and photophobia in childhood, 1,2 and renal failure at approximately 10 years of age. 8 After kidney transplantation, nonrenal complications occur, 9 including a distal vacuolar myopathy, 10,11 swallowing dysfunction, 12 diabetes mellitus, 13 male hypogonadism, 14 pulmonary dysfunction, 15 and central nervous system involvement, including idiopathic intracranial hypertension The renal glomerular deterioration of cystinosis can be prevented or retarded by the regular oral administration of a cystine-depleting agent, cysteamine bitartrate, or Cystagon (Mylan Pharmaceuticals, Morgantown, WV), which is now accepted as the treatment of choice for cystinosis throughout the world. In addition, there is evidence that nonrenal tissues, such as the thyroid 22 and the swallowing muscles, 23 can benefit from oral cysteamine therapy, and cysteamine eye drops can dissolve the corneal crystals of cystinosis In general, the liver does not appear to be impaired functionally in nephropathic cystinosis. Nevertheless, cystine crystals are abundant within this organ, 1,2 and hepatomegaly has been reported in approximately one third of patients older than 10 years of age 27 who were not well treated with cysteamine. Moreover, there have been isolated reports of hepatic veno-occlusive disease 28 and noncirrhotic portal hypertension in cystinosis patients. We now report 2 additional cases of severe portal hypertension in young men with nephropathic cystinosis, and show nodular regenerative hyperplasia (NRH) as the histologic basis for this pathophysiology. Abbreviation used in this paper: NRH, nodular regenerative hyperplasia by the American Gastroenterological Association Institute /06/$32.00 PII: /S (05)

2 388 O BRIEN ET AL CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 4, No. 3 Materials and Methods Diagnosis Nephropathic cystinosis was diagnosed based on characteristic clinical findings plus an increased leukocyte cystine content, which was determined by using the cystine binding protein assay. 32 The presence of corneal crystals confirmed the diagnosis. Mutation analysis of the CTNS gene initially was directed against the most common mutation, a 57-kb deletion, 4,33 using a multiplex polymerase chain reaction assay. 34,35 Both patients were enrolled in a protocol approved by the Institutional Review Board of the National Human Genome Research Institute, and gave written informed consent. Case Reports Patient 1 A 19-year-old white man was referred to the National Institutes of Health Clinical Center for evaluation of nephropathic cystinosis and for an undefined chronic liver disease. The patient was diagnosed with cystinosis at 17 months of age. His renal tubular Fanconi syndrome was treated symptomatically with replacement therapy, but he was unable to tolerate sustained oral cysteamine therapy at any time point. Chronic renal failure ensued and at age 9 years peritoneal dialysis was instituted. Over the next 7 years the patient experienced repeated episodes of peritonitis requiring hospitalization and antibiotic therapy. Hemodialysis was begun at age 16; ascites noted at that time was attributed to residual damage to the peritoneal membrane as a result of repeated episodes of peritonitis. At age 17 the patient received a cadaveric renal allograft without complications; posttransplant he received 2 months of azathioprine, in addition to maintenance therapy with prednisone and cyclosporine. Approximately 6 months after transplantation, he presented to a local emergency room with large volume and painless hematemesis. Further evaluation showed hepatosplenomegaly, ascites, gastroesophageal varices, gastritis, mildly increased liver function tests, and a wedged hepatic pressure of 28 mm Hg; the portosystemic gradient was 18 mm Hg. Viral hepatitis panels were negative, and there was no history of alcohol abuse. Liver biopsy examination showed no evidence of presinusoidal or postsinusoidal obstructive disease. The bleeding was controlled with sclerotherapy, and the patient was placed on propanolol 40 mg twice a day. Subsequently, repeated episodes of gastrointestinal bleeding required band ligation of varices, cauterization of a gastric ulcer, and transfusion of more than 100 U of blood. The patient was unable to tolerate somatostatin analogues because of severe blood pressure fluctuations. Approximately 6 months after his first gastrointestinal bleed, the patient began experiencing mental status changes associated with bouts of hyperammonemia, which appeared to coincide with the bleeding episodes. Episodes of fatigue and lethargy became more frequent, with sustained mild increases in ammonia level, in the range of mol/l. Daily lactulose therapy was initiated, but was not sufficient to manage the intermittent episodes of hyperammonemia and encephalopathy. On admission to the National Institutes of Health Clinical Center, physical examination showed an illappearing short white man with obvious ascites and scleral icterus. Palmar erythema, spider angiomata, and caput medusae also were present. Cranial nerve functions and reflexes were normal, without asterixis or cognitive slowing. Coarse crackles and dull percussion tones were present at the lung bases. A soft grade II/VI systolic murmur was heard, with no other adventitious heart sounds; there was no jugular venous distention, but 1 bilateral pitting edema was present in the lower extremities. Laboratory and imaging studies confirmed the diagnoses of nephropathic cystinosis and renal insufficiency. The leukocyte cystine level was increased markedly at 21 nmol of half-cystine/mg of protein (normal,.2). Molecular diagnostic testing showed homozygosity for the common 57-kb deletion. 4,33 The calculated creatinine clearance, based on serum creatinine and height, was 39 ml/min/1.73 m 2. Serum ceruloplasmin and -1 antitrypsin levels were normal. A noncontrast computed tomography scan of the abdomen showed gross hepatosplenomegaly and extensive peritoneal calcifications; the capsule of the liver also had calcifications. Serologic evaluations were negative for metabolic, infectious, inflammatory, or autoimmune causes of liver disease. His peak total bilirubin level was 1.4 mg/dl. An echocardiogram showed no evidence of heart failure. Four days after admission the hemoglobin level decreased from 12.8 to 8.0 g/dl, and the patient developed acute confusion, speech difficulties, and asterixis. The ammonia level was more than 100 mol/l, and the patient was treated with intravenous fluid replacement and 2 U of packed red blood cells. The confusion and speech difficulties improved within a few hours. Upper endoscopy revealed varices involving the antrum and the duodenum, severe portal gastropathy with oozing, and probable varices in the duodenal bulb and the second portion of the duodenum. Examination of the colon revealed friable and markedly edematous mucosa, with clots and active bleeding. Fresh blood also was noted in

3 March 2006 NRH IN CYSTINOSIS 389 Table 1. Laboratory and Test Results Patient 1 Patient 2 Normal values Baseline laboratory results Leukocyte count, k/ L Hemoglobin, g/dl Platelet count, k/ L Serum sodium, mmol/l Serum creatinine, mg/dl ESR, mm/h Alkaline phosphatase, U/L Alanine/aspartate 56/67 17/ /9 34 transaminase, U/L GGT, U/L Total bilirubin, mg/dl Direct bilirubin, mg/dl Serum ammonia, mol/l 76 a Prothrombin time, s International normalized ratio, s Albumin, g/dl Hepatitis A, B, C screen Negative Negative Negative Spleen size, cm ND Portal vein diameter, mm ND Hepatic pressures Wedged hepatic vein, mm Hg Free hepatic vein, mm Hg Hepatic vein gradient, mm Hg Ascites fluid Serum-ascites albumin NA gradient (g/dl) Peritoneal-serum total protein gradient (g/dl) NA ESR, erythrocyte sedimentation rate; GGT, gamma glutamyltranspeptidase; ND, not done; NA, not applicable. a After treatment. the terminal ileum; the source appeared to be distal to the duodenum, but proximal to the terminal ileum. Paracentesis, a transjugular liver biopsy examination, and hepatic pressure measurements were performed and 800 ml of clear ascitic fluid was removed. The results of the procedure and of the peritoneal fluid analysis (Table 1) were consistent with portal hypertension. There was no serologic evidence of a viral cause to his liver disease, and cytologic examination and cultures of the peritoneal fluid were negative. Liver biopsy examinations were performed at 17 and 18 years of age. The results were similar, but the pathology was more evident in the second biopsy examination. On that sample, the hepatic parenchyma was vaguely nodular on routine stains, with scattered clusters of foamy macrophages. Crystalline material was not seen. There was minimal inflammation, consisting mainly of a sparse portal inflammatory infiltrate and rare foci of lobular inflammation. The Masson trichrome stain showed mild portal fibrotic expansion and mild perisinusoidal fibrosis, particularly in acinar zone 3. There was no bridging fibrosis. On reticulin stain there were obvious nodules of hepatocytes with widened liver cell plates that were indicative of regeneration. Between these nodules, liver cells were compressed and atrophic (Figure 1). There was no evidence of portal vein obliteration or veno-occlusive changes. The patient s propanolol dose was increased to 50 mg twice a day, achieving a 25% reduction in systolic blood pressure. A 2 g/day sodium diet was instituted, and the doses of spironolactone, furosemide, and lactulose were titrated for control of the ascites and encephalopathy. The patient was considered for a surgical portosystemic shunt, but declined. He died of fulminant bacterial peritonitis 12 months later. Patient 2 A 30-year-old white man was referred to the National Institutes of Health Clinical Center for evaluation of nephropathic cystinosis and hypersplenism. He had been diagnosed with cystinosis at approximately 17 months of age and never was compliant with oral cysteamine therapy. He developed end-stage renal disease at age 13, and soon after received a renal allograft from his father, obviating the need for dialysis. He was discovered to have splenic enlargement at age 24. He developed ascites in his late 20s and began feeling progressively more dyspneic with normal activities. At age 29, he began to receive monthly blood transfusions for pancytopenia, with hemoglobin levels ranging between 6 and 8 g/dl, leukocyte counts between 1.5 and 2.5 k/ L, and platelet counts ranging from 16 to 30 k/ L. His serum creatinine level increased progressively from approximately 2.5 mg/dl to more than 4 mg/dl. There was no history of alcohol or injection drug abuse, viral hepatitis, or azathioprine use. Because of his worsening hypersplenism, the patient was referred to a hematologist/ oncologist for evaluation; a bone marrow biopsy examination showed the presence of cystine crystals, but was negative for myeloproliferative disease. The patient was referred to the National Institutes of Health Clinical Center for splenectomy consideration. On admission the patient was noticeably dyspneic with gross ascites, massive splenomegaly, and asterixis, but no icterus or jaundice. His liver was not enlarged or tender. His pulse and blood pressure were normal, his respiratory rate was 24 and labored, and his peripheral oxygen saturation was 96% on room air. He had prominent abdominal veins and bilateral gynecomastia. Cognition was slow but intact. There also were decreased breath sounds in his lung bases, orthopnea, a grade III/VI systolic murmur, and a pulmonic component to his second heart sound. There was mild bilateral pitting

4 390 O BRIEN ET AL CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 4, No. 3 Figure 1. Representative photomicrographs of the second liver biopsy specimen from patient 1. (A) Routine staining shows unremarkable hepatic parenchyma with only a suggestion of nodularity (H&E, original magnification, 10 ). (B) Mild portal fibrotic expansion is apparent in most of the portal areas. The portal vein is present (Masson trichrome, original magnification, 10 ). (C) Delicate perisinusoidal fibrosis is present around the central veins (Masson trichrome, original magnification, 40 ). (D) The reticulin stain shows the nodularity of the hepatic parenchyma with alternating zones of compression and expansion of liver cell plates (reticulin, original magnification, 10 ). edema in the lower extremities. The admission chest radiograph showed atelectasis, but no cardiomegaly, effusions, or evidence of pulmonary edema. The laboratory results and initial imaging studies were consistent with nephropathic cystinosis, end-stage renal disease, and noncirrhotic portal hypertension (Table 1). The leukocyte cystine level was increased at 3.5 nmol of half-cystine/mg of protein. Molecular diagnostic testing showed homozygosity for the common 57-kb deletion. 4,33 The creatinine clearance was 25 ml/min/1.73 m 2. Serum ceruloplasmin, iron, transferrin, and -1 antitrypsin levels were normal, and a toxicology screen was negative. Abdominal ultrasound showed a markedly enlarged spleen measuring at least 25 cm, normal liver dimensions, and large-volume abdominal ascites. Portal blood flow was turbulent and the portal vein measured 1.8 cm. No other vascular abnormalities were noted. There was no serologic evidence of liver disease resulting from metabolic, infectious (Epstein Barr virus, cytomegalovirus, hepatitis C virus by polymerase chain reaction), inflammatory, or autoimmune (rheumatoid factor, antinuclear antibody, anti smooth muscle antibody, antiliver/kidney microsomal antibody) causes. The patient s pulmonary status was investigated further. An arterial blood gas analysis showed a PaO 2 of 56 mm Hg on room air, an oxygen saturation of 92%, ph of 7.30, PCO 2 of 45 mm Hg, and a bicarbonate level of 21 mmol/l. The alveolar to arterial gradient was 37.5 mm Hg. The patient was placed on supplemental oxygen and his dyspnea improved. A 2-dimensional transthoracic echocardiogram and bubble study showed mild to moderate pulmonary hypertension, and delayed appearance of bubbles in the left side of the heart. The differential diagnosis included portopulmonary hypertension and hepatopulmonary syndrome. Subsequent pulmonary function tests were consistent with severe restrictive disease caused by muscle wasting. The forced vital capacity was 28% of predicted, the forced expiratory volume was 28%, and the total lung capacity was 40%. The patient refused additional pulmonary function testing. On the third day after admission, the patient underwent a transjugular liver biopsy procedure with diagnostic and therapeutic paracentesis, and hepatic and systemic vascular pressure measurements. The results of the peritoneal fluid analysis and pressure measurements (Table 1) were consistent with portal hypertension. Cytologic examination and culture results were negative. Examination of the liver biopsy specimen showed focal regenerative changes suggestive of NRH (Figure 2). The hepatic architecture largely was preserved and there was no significant portal inflammatory infiltrate or lobular

5 March 2006 NRH IN CYSTINOSIS 391 inflammation. The bile ducts were intact and some of the portal veins appeared slit like. No crystalline material or steatosis was noted, but there were groups of enlarged periodic acid Schiff negative macrophages with clear vacuolated cytoplasm. The reticulin stain showed nodularity with alternating zones of hepatocyte regeneration and hepatocyte plate compression. Focal sinusoidal dilatation also was noted. After recovering from the liver biopsy examination, the patient decided to forego further evaluation and treatment, which would have included endoscopic screening for gastroesophageal varices. Although he had no history of gastroesophageal varices, he did have rectal bleeding attributable to external hemorrhoids. The options of a surgical shunt and a combined liver and kidney transplantation were presented to the patient, but he returned home, refusing further treatment. Figure 2. Representative photomicrographs of the liver biopsy specimen from patient 2. (A) Clusters of vacuolated macrophages were seen in sinuses adjacent to central veins. There also is mild sinusoidal dilatation adjacent to the sinuses that are filled with macrophages (H&E, original magnification, 20 ). (B) On reticulin stain there were some areas that showed widened liver cell plates, with 2 or 3 hepatocytes between layers of reticulin (reticulin, original magnification, 40 ). (C) Elsewhere, particularly in the vicinity of central veins, there was compression of liver cell plates with accentuation of reticulin (reticulin, original magnification, 40 ). Discussion Although the liver has been considered largely spared in patients with nephropathic cystinosis, hepatomegaly remains a commonly recognized feature of the disease. 27,36 In addition, isolated reports of functional defects have appeared over the past 2 decades (Table 2). In all cases, exposure to cysteamine therapy was negligible. Early indications of liver involvement in cystinosis were presented by Broyer et al, 36 who described the medical history of 19 posttransplant cystinosis patients ages years. They found hepatomegaly in 10 individuals, and signs of portal hypertension in 3, all of whom developed esophageal varices with mild digestive tract bleeding and splenomegaly; 1 patient had ascites. Sonography showed signs of latent portal hypertension in 4 other patients. All the patients with evidence of portal hypertension were at least 16 years old, and most of the patients had normal liver function test results. 36 Compliance with cysteamine therapy was not reported, but all 19 patients had leukocyte cystine levels more than 10 times the accepted normal level of less than.2 nanomole of half-cystine/mg protein. In 1983, Avner et al 28 described an 8-year-old boy with cystinosis and hepatomegaly, gastric varices, increased portal pressure, ascites, and a prominent venous pattern on the abdomen. The diagnosis was given as hepatic veno-occlusive disease, and the investigators attributed this to cysteamine treatment. This etiology was questioned because of the small amount of drug this patient received. 37 In addition, no subsequent cases of hepatic veno-occlusive disease have been attributed to

6 392 O BRIEN ET AL CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 4, No. 3 Table 2. Comparison of Liver Biopsy Examination Findings Case Avner et al 28 Broyer et al 36 Klenn and Rubin 30 DiDomenico et al 31 Rossi et al 29 Patient 1 Patient 2 Age, y Genotype NR NR NR NR NR 57-kb del 57-kb del Cysteamine use 1 y NR NR Noncompliant Noncompliant 1 y 1 y Microarchitecture NL NL NL NL NL Distorted, NL regenerative nodules Hepatocyte NL NL Perisinusoid NL Perisinusoid NL NL morphology atrophy atrophy Kupffer cell morphology Irregular, crystals Large, foamy Large, foamy Hypertrophic Hypertrophic NL Large, foamy Sinusoidal morphology Marked fibrosis, especially centrilobular Nodules of Kupffer cells Widening of spaces and collagen deposition Collagen deposition NL Collagen deposition Mild fibrosis Mild fibrosis, focal sinusoidal dilatation NL Periportal space NR Large Kupffer cells NL Nonbridging fibrosis Fibrosis Evidence of NRH NR NR No NR No Yes Yes Viral studies Negative for NR Negative for Negative Negative Negative Negative hepatitis B, C hepatitis B, C NR, not reported; NL, normal. the use of cysteamine, despite its administration to more than 400 patients for up to 20 years. In 1994, Klenn and Rubin 30 published a report of a 24-year-old man with nephropathic cystinosis who had undergone 4 renal transplants and who eventually died from sepsis. This patient had marked ascites and fibrocongestive splenomegaly without significant liver function abnormalities. In 2004, DiDomenico et al 31 presented evidence of portal hypertension in an 18-year-old woman with cystinosis who had a renal transplant and a history of poor compliance with cysteamine. She presented with normal liver function, asymptomatic splenomegaly, an enlarged portal vein, and grade 1 esophageal varices, but did not show evidence of ascites, hepatomegaly, or encephalopathy. Finally, Rossi et al 29 described portal hypertension without significant fibrosis in a 26- year-old man with nephropathic cystinosis. The cause of the portal hypertension and liver disease in all these patients, including ours, remains unclear. However, certain characteristics tie the cases together. First, none of the patients received any significant amount of cystine-depleting therapy. Consequently, hepatic cystine levels are expected to be in the same range as for untreated patients (ie, 100 nmol half-cystine/mg wet weight, or times the normal range). 38 Such massive amounts of cystine were not documented in our patients because the extra passes on transjugular biopsy examination that would be required to assay for cystine could not be justified medically. In addition, crystals present in liver macrophages may have been dissolved during fixation; several published pathology reports of liver disease in cystinosis have indicated vacuoles or obvious crystals present within hepatic macrophages. A second commonality is that none of the patients showed cirrhosis. Third, there was no evidence of a viral cause to the liver disease in any of the patients. Moreover, no toxic metabolites or pharmacologic causes were implicated. Rather, we believe that these cases may have in common a gradual progression to NRH, which is seen in a wide variety of disease states. Our patients showed changes characteristic of NRH; this was accompanied by distortion of the liver microarchitecture and, in patient 1, periportal and sinusoidal fibrosis. Although NRH was not noted in the previous reports, periportal or sinusoidal fibrosis was described in at least 3 other biopsy examinations performed on our patients. The histologic changes seen in NRH are, in general, difficult to diagnose without a reticulin stain, a point that has been made recently in another series of drug-induced NRH. 39 Hence, some of the other cases listed in Table 2 also could represent NRH because they feature portal hypertension with relatively intact hepatic synthetic function, a cardinal finding of NRH. NRH is a recognized complication of patients with renal transplants, Felty s syndrome and other autoimmune disorders, 44 and lymphoproliferative or myeloproliferative disorders. 45 The cause of NRH is not understood but has been attributed to hepatic vascular obstruction (especially portal vein obstruction) or to a proliferative disorder of the liver. 46 Altered hepatic blood flow may lead to ischemia, resulting in atrophy

7 March 2006 NRH IN CYSTINOSIS 393 and the formation of regenerative nodules. 44,47 In renal transplant recipients, cytomegalovirus 48 and azathioprine 49 have been suggested to be causative agents, although the mechanism is not known. Our patients had renal transplants but were not exposed to azathioprine or cytomegalovirus before their presentation with symptoms of the liver disorder. Patient 1 did receive azathioprine for approximately 2 months, but the signs and symptoms of portal hypertension had been present before starting the medication. In addition, imaging studies and laboratory tests showed no evidence of portal vein obstruction or an autoimmune or proliferative hematologic disorder. Several conclusions follow from the cases described earlier. First, liver disease can be added to the growing list of late complications of nephropathic cystinosis. In these individuals, the extent of liver involvement varies considerably, from none to simple hepatomegaly to fatal portal hypertension. Second, the histology of the liver disease of cystinosis appears consistent in many cases with NRH; reticulin staining should be performed on any biopsy specimens. Third, there should be a high index of suspicion for portal hypertension among older cystinosis patients. Fourth, cysteamine almost certainly is not the toxic agent in patients with liver disease. 37 Finally, the best therapy remains prophylaxis by means of the cystine-depleting agent, cysteamine, which has proven efficacy in preventing renal glomerular deterioration, 20,21 enhancing growth, 20,21 preventing the need for thyroid replacement, 22 staving off swallowing difficulties, 23 and even depleting the liver itself of its crystalline cystine load. 38 References 1. Gahl WA, Thoene JG, Schneider JA. Cystinosis: a disorder of lysosomal membrane transport. 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8 394 O BRIEN ET AL CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 4, No Oshima RG, Willis RC, Furlong CE, et al. Binding assays for amino acids. J Biol Chem 1974;249: Shotelersuk V, Larson D, Anikster Y, et al. CTNS mutations in an American-based population of cystinosis patients. Am J Hum Genet 1998;63: Anikster Y, Lucero C, Touchman JW, et al. Identification and detection of the common 65-kb deletion breakpoint in the nephropathic cystinosis gene (CTNS). Mol Genet Metab 1999;66: Kleta R, Anikster Y, Lucero C, et al. CTNS mutations in African American patients with cystinosis. Mol Genet Metab 2001;74: Broyer M, Tete MJ, Gubler MC. Late symptoms in infantile cystinosis. Pediatr Nephrol 1987;1: Gahl WA, Schulman JD, Thoene JG, et al. Hepato-toxicity of cysteamine. J Pediatr 1983;103: Gahl WA, Charnas L, Markello TC, et al. Parenchymal organ cystine depletion with long term cysteamine therapy. Biochem Med Metab Biol 1992;48: Geller SA, Dubinsky MC, Poordad FF, et al. Early hepatic nodular hyperplasia and submicroscopic fibrosis associated with 6-thioguanine therapy in inflammatory bowel disease. Am J Surg Pathol 2004;28: Buffet C, Cantarovitch M, Pelletier G, et al. Three cases of nodular regenerative hyperplasia of the liver following renal transplantation. Nephrol Dial Transplant 1988;3: Morales JM, Prieto C, Colina F, et al. Nodular regenerative hyperplasia of the liver in renal transplantation. Transplant Proc 1987; 19: Naber AH, VanHaelst U, Yap SH. Nodular regenerative hyperplasia of the liver: an important cause of portal hypertension in non-cirrhotic patients. J Hepatol 1991;12: Bredfeldt JE, Havey AL. Nodular regenerative hyperplasia of the liver following renal transplantation. Dig Dis Sci 1981;26: Thiele D. Hepatic manifestations of systemic disease and other disorders of the liver. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger and Fordtran s gastrointestinal and liver disease: pathophysiology/diagnosis/management. 7th ed. Philadelphia: Saunders, 2002: Al-Mukhaizeem KA, Rosenberg A, Sherker AH. Nodular regenerative hyperplasia of the liver: an under-recognized cause of portal hypertension in hematological disorders. Am J Hematol 2004; 75: Mahamid J, Miselevich I, Attias D, et al. Nodular regenerative hyperplasia associated with idiopathic thrombocytopenic purpura in a young girl: a case report and review of the literature. J Pediatr Gastroenterol Nutr 2005;41: Shimamatsu K, Wanless IR. Role of ischemia in causing apoptosis, atrophy, and nodular hyperplasia in human liver. Hepatology 1997;26: Mourad G, Bories P, Bethelemy C, et al. Peliosis hepatis and nodular regenerative hyperplasia of the liver in renal transplants. Is cytomegalovirus the cause of this severe disease? Transplant Proc 1987;19: Jones MC, Best PV, Catto GR. Is nodular regenerative hyperplasia of the liver associated with azathioprine therapy after renal transplantation? Nephrol Dial Transplant 1988;3: Address requests for reprints to: William A. Gahl, MD, PhD, 10 Center Drive, MSC 1851, Building 10, Room 10C-103, NHGRI, National Institutes of Health, Bethesda, Maryland bgahl@helix.nih.gov; fax: (301) Supported in part by the Intramural Research Programs of the National Institutes of Health, specifically, those of the National Human Genome Research Institute, the National Institute of Diabetes and Digestive and Kidney Diseases, and the National Cancer Institute, Center for Cancer Research.