Hepatocellular carcinoma complicating liver cirrhosis in type IIIa glycogen storage disease

Glycogen storage diseases: An update

Glycogen storage diseases (GSDs), also referred to as glycogenoses, are inherited metabolic disorders of glycogen metabolism caused by deficiency of enzymes or transporters involved in the synthesis or degradation of glycogen leading to aberrant storage and/or utilization. The overall estimated GSD incidence is 1 case per 20000-43000 live births. There are over 20 types of GSD including the subtypes. This heterogeneous group of rare diseases represents inborn errors of carbohydrate metabolism and are classified based on the deficient enzyme and affected tissues. GSDs primarily affect liver or muscle or both as glycogen is particularly abundant in these tissues. However, besides liver and skeletal muscle, depending on the affected enzyme and its expression in various tissues, multiorgan involvement including heart, kidney and/or brain may be seen. Although GSDs share similar clinical features to some extent, there is a wide spectrum of clinical phenotypes. Currently, the goal of treatment is to maintain glucose homeostasis by dietary management and the use of uncooked cornstarch. In addition to nutritional interventions, pharmacological treatment, physical and supportive therapies, enzyme replacement therapy (ERT) and organ transplantation are other treatment approaches for both disease manifestations and long-term complications. The lack of a specific therapy for GSDs has prompted efforts to develop new treatment strategies like gene therapy. Since early diagnosis and aggressive treatment are related to better prognosis, physicians should be aware of these conditions and include GSDs in the differential diagnosis of patients with relevant manifestations including fasting hypoglycemia, hepatomegaly, hypertransaminasemia, hyperlipidemia, exercise intolerance, muscle cramps/pain, rhabdomyolysis, and muscle weakness. Here, we aim to provide a comprehensive review of GSDs. This review provides general characteristics of all types of GSDs with a focus on those with liver involvement.

Diurnal variability of glucose tetrasaccharide (Glc4) excretion in patients with glycogen storage disease type III

AIM

The urinary glucose tetrasaccharide, Glcα1-6Glcα1-4Glcα1-4Glc (Glc4), is a glycogen limit dextrin that is elevated in patients with glycogen storage disease (GSD) type III. We evaluated the potential of uncooked cornstarch therapy to interfere with Glc4 monitoring, by measuring the diurnal variability of Glc4 excretion in patients with GSD III.

METHODS

Voids were collected at home over 24 hours, stored at 4°C and frozen within 48 hours. Glc4 was analyzed using liquid chromatography-tandem mass spectrometry and normalized to creatinine.

RESULTS

Subjects with GSD III (median age: 13.5 years, range: 3.7-62; n = 18) completed one or more 24-hour urine collection, and 28/36 collections were accepted for analysis. Glc4 was elevated in 16/18 subjects (median: 13 mmol/mol creatinine, range: 2-75, reference range: <3). In collections with elevated Glc4 (23/28), two-thirds (15/23) had low diurnal variability in Glc4 excretion (coefficient of variation [CV%] <25). The diurnal variability was significantly correlated with the Glc4 concentration (Pearson R = .644, P < .05), but not with the dose of uncooked cornstarch. High intraday variability (>25%) was not consistently observed in repeat collections by the same subject.

CONCLUSIONS

The extent and variability of Glc4 excretion relative to creatinine was not correlated with cornstarch dose. A majority of collections showed low variability over 24 hours. These findings support the use of single time-point collections to evaluate Glc4 in patients with GSD III treated with cornstarch. However, repeat sampling over short time-periods will provide the most accurate assessment of Glc4 excretion, as intraday variability may be increased in patients with high Glc4 excretion.

Preclinical Research in Glycogen Storage Diseases: A Comprehensive Review of Current Animal Models

GSD are a group of disorders characterized by a defect in gene expression of specific enzymes involved in glycogen breakdown or synthesis, commonly resulting in the accumulation of glycogen in various tissues (primarily the liver and skeletal muscle). Several different GSD animal models have been found to naturally present spontaneous mutations and others have been developed and characterized in order to further understand the physiopathology of these diseases and as a useful tool to evaluate potential therapeutic strategies. In the present work we have reviewed a total of 42 different animal models of GSD, including 26 genetically modified mouse models, 15 naturally occurring models (encompassing quails, cats, dogs, sheep, cattle and horses), and one genetically modified zebrafish model. To our knowledge, this is the most complete list of GSD animal models ever reviewed. Importantly, when all these animal models are analyzed together, we can observe some common traits, as well as model specific differences, that would be overlooked if each model was only studied in the context of a given GSD.

Liver fibrosis during clinical ascertainment of glycogen storage disease type III: a need for improved and systematic monitoring

PURPOSE

In glycogen storage disease type III (GSD III), liver aminotransferases tend to normalize with age giving an impression that hepatic manifestations improve with age. However, despite dietary treatment, long-term liver complications emerge. We present a GSD III liver natural history study in children to better understand changes in hepatic parameters with age.

METHODS

We reviewed clinical, biochemical, histological, and radiological data in pediatric patients with GSD III, and performed a literature review of GSD III hepatic findings.

RESULTS

Twenty-six patients (median age 12.5 years, range 2-22) with GSD IIIa (n = 23) and IIIb (n = 3) were enrolled in the study. Six of seven pediatric patients showed severe fibrosis on liver biopsy (median [range] age: 1.25 [0.75-7] years). Markers of liver injury (aminotransferases), dysfunction (cholesterol, triglycerides), and glycogen storage (glucose tetrasaccharide, Glc₄) were elevated at an early age, and decreased significantly thereafter (p < 0.001). Creatine phosphokinase was also elevated with no significant correlation with age (p = 0.4).

CONCLUSION

Liver fibrosis can occur at an early age, and may explain the decrease in aminotransferases and Glc₄ with age. Our data outlines the need for systematic follow-up and specific biochemical and radiological tools to monitor the silent course of the liver disease process.

Glucose-free/high-protein diet improves hepatomegaly and exercise intolerance in glycogen storage disease type III mice

Glycogen disease type III (GSDIII), a rare incurable autosomal recessive disorder due to glycogen debranching enzyme deficiency, presents with liver, heart and skeletal muscle impairment, hepatomegaly and ketotic hypoglycemia. Muscle weakness usually worsens to fixed myopathy and cardiac involvement may present in about half of the patients during disease. Management relies on careful follow-up of symptoms and diet. No common agreement was reached on sugar restriction and treatment in adulthood.

We administered two dietary regimens differing in their protein and carbohydrate content, high-protein (HPD) and high-protein/glucose-free (GFD), to our mouse model of GSDIII, starting at one month of age. Mice were monitored, either by histological, biochemical and molecular analysis and motor functional tests, until 10 months of age.

GFD ameliorated muscle performance up to 10 months of age, while HPD showed little improvement only in young mice. In GFD mice, a decreased muscle glycogen content and fiber vacuolization was observed, even in aged animals indicating a protective role of proteins against skeletal muscle degeneration, at least in some districts. Hepatomegaly was reduced by about 20%. Moreover, the long-term administration of GFD did not worsen serum parameters even after eight months of high-protein diet. A decreased phosphofructokinase and pyruvate kinase activities and an increased expression of Krebs cycle and gluconeogenesis genes were seen in the liver of GFD fed mice.

Our data show that the concurrent use of proteins and a strictly controlled glucose supply could reduce muscle wasting, and indicate a better metabolic control in mice with a glucose-free/high-protein diet.

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GSDIII is a rare incurable disease due to lacking of glycogen debrancher enzyme.

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Essential features are liver, heart and skeletal muscle impairment.

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Two diets differing in protein and sugar amount were tested in Agl-mouse model.

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Glucose-free/high-protein diet decreased glycogen storage and hepatomegaly.

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Improved muscle performance and better metabolic compensation were achieved.

Inhibition of Glycogen Synthase II with RNAi Prevents Liver Injury in Mouse Models of Glycogen Storage Diseases

Glycogen storage diseases (GSDs) of the liver are devastating disorders presenting with fasting hypoglycemia as well as hepatic glycogen and lipid accumulation, which could lead to long-term liver damage. Diet control is frequently utilized to manage the potentially dangerous hypoglycemia, but there is currently no effective pharmacological treatment for preventing hepatomegaly and concurrent liver metabolic abnormalities, which could lead to fibrosis, cirrhosis, and hepatocellular adenoma or carcinoma. In this study, we demonstrate that inhibition of glycogen synthesis using an RNAi approach to silence hepatic Gys2 expression effectively prevents glycogen synthesis, glycogen accumulation, hepatomegaly, fibrosis, and nodule development in a mouse model of GSD III. Mechanistically, reduction of accumulated abnormally structured glycogen prevents proliferation of hepatocytes and activation of myofibroblasts as well as infiltration of mononuclear cells. Additionally, we show that silencing Gys2 expression reduces hepatic steatosis in a mouse model of GSD type Ia, where we hypothesize that the reduction of glycogen also reduces the production of excess glucose-6-phosphate and its subsequent diversion to lipid synthesis. Our results support therapeutic silencing of GYS2 expression to prevent glycogen and lipid accumulation, which mediate initial signals that subsequently trigger cascades of long-term liver injury in GSDs.

Medical-Nutritional Intervention in a Jordanian Child with Glycogen Storage Disease Type IIIA: Case Report

Background: Glycogen storage disease (GSD) type IIIa is a rare inborn error of metabolism characterized by a deficiency in glycogen disbranching enzymes. Nutritional intervention is a cornerstone in the medical care plane.

Case presentation: A 2-year-old Jordanian male, who is known to have GSD IIIa since he was 4 months was admitted because of infection. The child was on a special diet (small, frequent meals of complex carbohydrates and protein, avoiding simple sugars and fasting is prohibited). The child showed good activity level and a good appetite.

Method: The medical-nutritional intervention of GSD IIIa was evaluated by retrograde reviewing the child BMI, blood and biochemical tests on presentation and a month later visit.

Results: The biochemical tests included: blood glucose, urea, creatinine, cholesterol, triglycerides, albumin, total bilirubin, aspartate amino transferase (AST), alanine aminotransferase (ALT) and WBCs were decreased after nutritional intervention, however, the RBCs blood test was increased. On presentation, the child’s weight and height were documented as above the 15th and at 97th percentile respectively for his age, no change after the one month later visit was observed.

Conclusion: The biochemical and blood tests improved at the one-month follow-up visit vs. baseline. The individualized medical-nutritional intervention is a cornerstone in the management of GSD IIIa as part of a comprehensive medical care process.

Preclinical Development of New Therapy for Glycogen Storage Diseases

Glycogen storage disease (GSD) consists of more than 10 discrete conditions for which the biochemical and genetic bases have been determined, and new therapies have been under development for several of these conditions. Gene therapy research has generated proof-of-concept for GSD types I (von Gierke disease) and II (Pompe disease). Key features of these gene therapy strategies include the choice of vector and regulatory cassette, and recently adeno-associated virus (AAV) vectors containing tissue-specific promoters have achieved a high degree of efficacy. Efficacy of gene therapy for Pompe disease depend upon the induction of immune tolerance to the therapeutic enzyme. Efficacy of von Gierke disease is transient, waning gradually over the months following vector administration. Small molecule therapies have been evaluated with the goal of improving standard of care therapy or ameliorating the cellular abnormalities associated with specific GSDs. The receptor-mediated uptake of the therapeutic enzyme in Pompe disease was enhanced by administration of β2 agonists. Rapamycin reduced the liver fibrosis observed in GSD III. Further development of gene therapy could provide curative therapy for patients with GSD, if efficacy from preclinical research is observed in future clinical trials and these treatments become clinically available.

Targeting glycogen metabolism in bladder cancer

Metabolism has been a heavily investigated topic in cancer research for the past decade. Although the role of aerobic glycolysis (the Warburg effect) in cancer has been extensively studied, abnormalities in other metabolic pathways are only just being understood in cancer. One such pathway is glycogen metabolism; its involvement in cancer development, particularly in urothelial malignancies, and possible ways of exploiting aberrations in this process for treatment are currently being studied. New research shows that the glycogen debranching enzyme amylo-α-1,6-glucosidase, 4-α-glucanotransferase (AGL) is a novel tumour suppressor in bladder cancer. Loss of AGL leads to rapid proliferation of bladder cancer cells. Another enzyme involved in glycogen debranching, glycogen phosphorylase, has been shown to be a tumour promoter in cancer, including in prostate cancer. Studies demonstrate that bladder cancer cells in which AGL expression is lost are more metabolically active than cells with intact AGL expression, and these cells are more sensitive to inhibition of both glycolysis and glycine synthesis--two targetable pathways. As a tumour promoter and enzyme, glycogen phosphorylase can be directly targeted, and preclinical inhibitor studies are promising. However, few of these glycogen phosphorylase inhibitors have been tested for cancer treatment in the clinical setting. Several possible limitations to the targeting of AGL and glycogen phosphorylase might also exist.

Glycogen storage disease type III: A novel Agl knockout mouse model

Glycogen storage disease type III is an autosomal recessive disease characterized by a deficiency in the glycogen debranching enzyme, encoded by AGL. Essential features of this disease are hepatomegaly, hypoglycemia, hyperlipidemia, and growth retardation. Progressive skeletal myopathy, neuropathy, and/or cardiomyopathy become prominent in adults. Currently, there is no available cure. We generated an Agl knockout mouse model by deletion of the carboxy terminus of the protein, including the carboxy end of the glucosidase domain and the glycogen-binding domain. Agl knockout mice presented serious hepatomegaly, but we did not observe signs of cirrhosis or adenomas. In affected tissues, glycogen storage was higher than in wild-type mice, even in the central nervous system which has never been tested in GSDIII patients. The biochemical findings were in accordance with histological data, which clearly documented tissue impairment due to glycogen accumulation. Indeed, electron microscopy revealed the disruption of contractile units due to glycogen infiltrations. Furthermore, adult Agl knockout animals appeared less prompt to move, and they exhibited kyphosis. Three-mo-old Agl knockout mice could not run, and adult mice showed exercise intolerance. In addition, older affected animals exhibited an accelerated respiratory rate even at basal conditions. This observation was correlated with severe glycogen accumulation in the diaphragm. Diffuse glycogen deposition was observed in the tongues of affected mice. Our results demonstrate that this Agl knockout mouse is a reliable model for human glycogenosis type III, as it recapitulates the essential phenotypic features of the disease.

Liver transplantation for malignancy: Current treatment strategies and future perspectives

In 1967, Starzl et al performed the first successful liver transplantation for a patient diagnosed with hepatoblastoma. In the following, liver transplantation was considered ideal for complete tumor resection and potential cure from primary hepatic malignancies. Several reports of liver transplantation for primary and metastatic liver cancer however showed disappointing results and the strategy was soon dismissed. In 1996, Mazzaferro et al introduced the Milan criteria, offering liver transplantation to patients diagnosed with limited hepatocellular carcinoma. Since then, liver transplantation for malignant disease is an ongoing subject of preclinical and clinical research. In this context, several aspects must be considered: (1) Given the shortage of deceased-donor organs, long-term overall and disease free survival should be comparable with results obtained in patients transplanted for non-malignant disease; (2) In this regard, living-donor liver transplantation may in selected patients help to solve the ethical dilemma of optimal individual patient treatment vs organ allocation justice; and (3) Ongoing research focusing on perioperative therapy and anti-proliferative immunosuppressive regimens may further reduce tumor recurrence in patients transplanted for malignant disease and thus improve overall survival. The present review gives an overview of current indications and future perspectives of liver transplantation for malignant disease.

Mouse model of glycogen storage disease type III

Glycogen storage disease type IIIa (GSD IIIa) is caused by a deficiency of the glycogen debranching enzyme (GDE), which is encoded by the Agl gene. GDE deficiency leads to the pathogenic accumulation of phosphorylase limit dextrin (PLD), an abnormal glycogen, in the liver, heart, and skeletal muscle. To further investigate the pathological mechanisms behind this disease and develop novel therapies to treat this disease, we generated a GDE-deficient mouse model by removing exons after exon 5 in the Agl gene. GDE reduction was confirmed by western blot and enzymatic activity assay. Histology revealed massive glycogen accumulation in the liver, muscle, and heart of the homozygous affected mice. Interestingly, we did not find any differences in the general appearance, growth rate, and life span between the wild-type, heterozygous, and homozygous affected mice with ad libitum feeding, except reduced motor activity after 50 weeks of age, and muscle weakness in both the forelimb and hind legs of homozygous affected mice by using the grip strength test at 62 weeks of age. However, repeated fasting resulted in decreased survival of the knockout mice. Hepatomegaly and progressive liver fibrosis were also found in the homozygous affected mice. Blood chemistry revealed that alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (ALP) activities were significantly higher in the homozygous affected mice than in both wild-type and heterozygous mice and the activity of these enzymes further increased with fasting. Creatine phosphokinase (CPK) activity was normal in young and adult homozygous affected mice. However, the activity was significantly elevated after fasting. Hypoglycemia appeared only at a young age (3 weeks) and hyperlipidemia was not observed in our model. In conclusion, with the exception of normal lipidemia, these mice recapitulate human GSD IIIa; moreover, we found that repeated fasting was detrimental to these mice. This mouse model will be useful for future investigation regarding the pathophysiology and treatment strategy of human GSD III.

Characterization of a canine model of glycogen storage disease type IIIa

Glycogen storage disease type IIIa (GSD IIIa) is an autosomal recessive disease caused by deficiency of glycogen debranching enzyme (GDE) in liver and muscle. The disorder is clinically heterogeneous and progressive, and there is no effective treatment. Previously, a naturally occurring dog model for this condition was identified in curly-coated retrievers (CCR). The affected dogs carry a frame-shift mutation in the GDE gene and have no detectable GDE activity in liver and muscle. We characterized in detail the disease expression and progression in eight dogs from age 2 to 16 months. Monthly blood biochemistry revealed elevated and gradually increasing serum alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (ALP) activities; serum creatine phosphokinase (CPK) activity exceeded normal range after 12 months. Analysis of tissue biopsy specimens at 4, 12 and 16 months revealed abnormally high glycogen contents in liver and muscle of all dogs. Fasting liver glycogen content increased from 4 months to 12 months, but dropped at 16 months possibly caused by extended fibrosis; muscle glycogen content continually increased with age. Light microscopy revealed significant glycogen accumulation in hepatocytes at all ages. Liver histology showed progressive, age-related fibrosis. In muscle, scattered cytoplasmic glycogen deposits were present in most cells at 4 months, but large, lake-like accumulation developed by 12 and 16 months. Disruption of the contractile apparatus and fraying of myofibrils was observed in muscle at 12 and 16 months by electron microscopy. In conclusion, the CCR dogs are an accurate model of GSD IIIa that will improve our understanding of the disease progression and allow opportunities to investigate treatment interventions.

Hepatocellular adenoma in glycogen storage disorder type I: a clinicopathological and molecular study

AIMS

  Glycogen storage disease type I is a metabolic disorder resulting from deficiency of the glucose-6-phosphate complex. Long-term complications include the development of hepatocellular adenoma (HCA). In this retrospective study, our aim was to reclassify according to geno-phenotypic characteristics nodular lesions identified in hepatectomy specimens of such patients transplanted between 1998 and 2008 at our institution.

METHODS AND RESULTS

  Clinicopathological data of seven consecutive transplanted patients with glycogen storage disease type I were reviewed. Liver nodules were re-examined histologically and by immunohistochemistry. Molecular analysis was performed additionally in a case with specific features. Four patients had multiple tumours. We concluded that 26 of 38 nodules available for study had features of inflammatory hepatocellular adenomas, seven comprised adenomas not otherwise specified and five were found to be focal nodular hyperplasia.

CONCLUSIONS

  Further studies are needed to clarify the pathogenesis of hepatocellular adenomas in glycogen storage disease; in particular to determine whether they share abnormal metabolic pathways with inflammatory adenomas in the general population. Testing for acute phase proteins may be a helpful tool in the early detection of HCA in such patients. Finally, there is a need to further define their risk of malignant transformation, in relation to age and possible cofactors.

Insights into the pathogenesis and treatment of cancer from inborn errors of metabolism

Mutations in genes that play fundamental roles in metabolic pathways have been found to also play a role in tumor development and susceptibility to cancer. At the same time, significant progress has been made in the treatment of patients with inborn errors of metabolism (IEM),(1) resulting in increased longevity and the unmasking of cancer predisposition, frequently hepatocellular carcinoma, in these conditions. These patients offer a potential opportunity to deepen our understanding of how intermediary metabolism impacts tumorigenesis. We provide an overview from the perspective of cancers in patients affected with IEM and discuss how dysregulation of these specific metabolic pathways might contribute to the mechanisms of cancer development and treatment.

Insights into the pathogenesis and treatment of cancer from inborn errors of metabolism

Mutations in genes that play fundamental roles in metabolic pathways have been found to also play a role in tumor development and susceptibility to cancer. At the same time, significant progress has been made in the treatment of patients with inborn errors of metabolism (IEM),(1) resulting in increased longevity and the unmasking of cancer predisposition, frequently hepatocellular carcinoma, in these conditions. These patients offer a potential opportunity to deepen our understanding of how intermediary metabolism impacts tumorigenesis. We provide an overview from the perspective of cancers in patients affected with IEM and discuss how dysregulation of these specific metabolic pathways might contribute to the mechanisms of cancer development and treatment.

Long-term results of living donor liver transplantation for glycogen storage disorders in children

Liver transplantation (LT) may be indicated in glycogen storage disorders (GSD) when medical treatment fails to control the metabolic problems or when hepatic adenomas develop. We present our institutional experience with living donor LT (LDLT) for children with GSD. A total of 244 patients underwent primary LDLT at our institution from June 1994 to December 2005. A total of 12 (5%) children (8 female and 4 male) were afflicted with GSD and were not responsive to medical treatment. Nine patients had GSD type I and 3 had GSD type III. The median age at the time of transplantation was 7.27 yr (range, 2.4-15.7). All patients presented with metabolic abnormalities, including hypoglycemia, and lactic acidosis. In addition, 4 patients presented with growth retardation. A total of 11 patients received left lobe grafts and 1 received a right lobe graft. The mean graft-to-recipient weight ratio was 1.25 (range, 0.89-1.61). Two patients had hepatic vein stenoses that were treated by balloon dilatation; 1 patient had bile leak, which settled spontaneously. The overall surgical morbidity rate was 25%. Three patients had hepatic adenomas in the explanted liver. There was a single mortality at 2 months posttransplantation due to acute pancreatitis and sepsis. The mean follow up was 47.45 months. The metabolic abnormalities were corrected and renal function remained normal. In patients with growth retardation, catch-up growth was achieved posttransplantation. In conclusion, LDLT is a viable option to restore normal metabolic balance in patients with GSD when medical treatment fails. Long-term follow-up after LT for GSD shows excellent graft and patient survival.

Glycogen storage disease type III-hepatocellular carcinoma a long-term complication?

BACKGROUND/AIMS

Glycogen storage disease III (GSD III) is caused by a deficiency of glycogen-debranching enzyme which causes an incomplete glycogenolysis resulting in glycogen accumulation with abnormal structure (short outer chains resembling limit dextrin) in liver and muscle. Hepatic involvement is considered mild, self-limiting and improves with age. With increased survival, a few cases of liver cirrhosis and hepatocellular carcinoma (HCC) have been reported.

METHODS

A systematic review of 45 cases of GSD III at our center (20 months to 67 years of age) was reviewed for HCC, 2 patients were identified. A literature review of HCC in GSD III was performed and findings compared to our patients.

CONCLUSIONS

GSD III patients are at risk for developing HCC. Cirrhosis was present in all cases and appears to be responsible for HCC transformation There are no reliable biomarkers to monitor for HCC in GSD III. Systematic evaluation of liver disease needs be continued in all patients, despite lack of symptoms. Development of guidelines to allow for systematic review and microarray studies are needed to better delineate the etiology of the hepatocellular carcinoma in patients with GSD III.

Glucogenosis tipo III asociada a carcinoma hepatocelular

Type III glycogen storage disease is a hereditary disorder with autosomal recessive transmission. It is characterized by accumulation of abnormal glycogen in the liver and, in 80% of patients, in muscle. The liver can also show fibrosis and sometimes cirrhosis. Until 2000, 9 cases of cirrhosis had been published, 3 of which showed associated hepatocarcinoma. We present the case of a 31-year-old woman, diagnosed in childhood with type III glycogen storage disease, who 30 years after onset developed a hepatocellular carcinoma with portal thrombosis in the context of advanced cirrhosis. This is the first case to be reported in the Spanish literature of type III glycogen storage disease associated with hepatocellular carcinoma.

Glycogen storage disease type III in Inuit children

Glycogen storage disease type III (GSD III) was diagnosed in 4 Inuit children (3 confirmed, 1 suspected case) at our institution over the last decade. This rare autosomal recessive disease, which results from a deficiency of the debranching enzyme required for complete degradation of the glycogen molecule, has not been previously described in this population. The possible clinical presentations are heterogeneous, as is the spectrum of severity of this disease. The long-term sequelae can be severe, including recurrent hypoglycemia, hepatic cirrhosis and progressive muscle weakness. These 4 cases would suggest an increased prevalence of GSD III in the Inuit population. Therefore, it is important for health care providers caring for this population to consider and recognize this rare but serious disease.