Bone mineral density and markers of bone turnover in patients with glycogen storage disease types I, III and IX

Endocrine involvement in hepatic glycogen storage diseases: pathophysiology and implications for care

Hepatic glycogen storage diseases constitute a group of disorders due to defects in the enzymes and transporters involved in glycogen breakdown and synthesis in the liver. Although hypoglycemia and hepatomegaly are the primary manifestations of (most of) hepatic GSDs, involvement of the endocrine system has been reported at multiple levels in individuals with hepatic GSDs. While some endocrine abnormalities (e.g., hypothalamic‑pituitary axis dysfunction in GSD I) can be direct consequence of the genetic defect itself, others (e.g., osteopenia in GSD Ib, insulin-resistance in GSD I and GSD III) may be triggered by the (dietary/medical) treatment. Being aware of the endocrine abnormalities occurring in hepatic GSDs is essential (1) to provide optimized medical care to this group of individuals and (2) to drive research aiming at understanding the disease pathophysiology. In this review, a thorough description of the endocrine manifestations in individuals with hepatic GSDs is presented, including pathophysiological and clinical implications.

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.

Glycogen storage disease type 1a in the Ohio Amish

Glycogen storage disease type 1a (GSD1a) is an inborn error of glucose metabolism characterized by fasting hypoglycemia, hepatomegaly, and growth failure. Late complications include nephropathy and hepatic adenomas. We conducted a retrospective observational study on a cohort of Amish patients with GSD1a. A total of 15 patients cared for at a single center, with a median age of 9.9 years (range 0.25–24 years) were included. All patients shared the same founder variant in GCPC c.1039 C > T. The phenotype of this cohort demonstrated good metabolic control with median cohort triglyceride level slightly above normal, no need for continuous overnight feeds, and a higher quality of life compared to a previous GSD cohort. The most frequent complications were oral aversion, gross motor delay, and renal hyperfiltration. We discuss our unique care delivery at a single center that cares for Amish patients with inherited disorders.

Evaluation of Glycogen Storage Patients: Report of Twelve Novel Variants and New Clinical Findings in a Turkish Population

Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders that disturb glycogen synthesis or utilization. Although it is one of the oldest inherited metabolic disorders, new genetic methods and long-time patient follow-ups provide us with unique insight into the genotype-phenotype correlations. The aim of this study was to share the phenotypic features and molecular diagnostic results that include new pathogenic variants in our GSD cases. Twenty-six GSD patients were evaluated retrospectively. Demographic data, initial laboratory and imaging features, and current findings of the patients were recorded. Molecular analysis results were classified as novel or previously defined variants. Novel variants were analyzed with pathogenicity prediction tools according to American College of Medical Genetics and Genomics (ACGM) criteria. Twelve novel and rare variants in six different genes were associated with the disease. Hearing impairment in two patients with GSD I, early peripheral neuropathy after liver transplantation in one patient with GSD IV, epilepsy and neuromotor retardation in three patients with GSD IXA were determined. We characterized a heterogeneous group of all diagnosed GSDs over a 5-year period in our institution, and identified novel variants and new clinical findings. It is still difficult to establish a genotype-phenotype correlation in GSDs.

A retrospective longitudinal study and comprehensive review of adult patients with glycogen storage disease type III

INTRODUCTION

A deficiency of glycogen debrancher enzyme in patients with glycogen storage disease type III (GSD III) manifests with hepatic, cardiac, and muscle involvement in the most common subtype (type a), or with only hepatic involvement in patients with GSD IIIb.

OBJECTIVE AND METHODS

To describe longitudinal biochemical, radiological, muscle strength and ambulation, liver histopathological findings, and clinical outcomes in adults (≥18 years) with glycogen storage disease type III, by a retrospective review of medical records.

RESULTS

Twenty-one adults with GSD IIIa (14 F & 7 M) and four with GSD IIIb (1 F & 3 M) were included in this natural history study. At the most recent visit, the median (range) age and follow-up time were 36 (19-68) and 16 years (0-41), respectively. For the entire cohort: 40% had documented hypoglycemic episodes in adulthood; hepatomegaly and cirrhosis were the most common radiological findings; and 28% developed decompensated liver disease and portal hypertension, the latter being more prevalent in older patients. In the GSD IIIa group, muscle weakness was a major feature, noted in 89% of the GSD IIIa cohort, a third of whom depended on a wheelchair or an assistive walking device. Older individuals tended to show more severe muscle weakness and mobility limitations, compared with younger adults. Asymptomatic left ventricular hypertrophy (LVH) was the most common cardiac manifestation, present in 43%. Symptomatic cardiomyopathy and reduced ejection fraction was evident in 10%. Finally, a urinary biomarker of glycogen storage (Glc4) was significantly associated with AST, ALT and CK.

CONCLUSION

GSD III is a multisystem disorder in which a multidisciplinary approach with regular clinical, biochemical, radiological and functional (physical therapy assessment) follow-up is required. Despite dietary modification, hepatic and myopathic disease progression is evident in adults, with muscle weakness as the major cause of morbidity. Consequently, definitive therapies that address the underlying cause of the disease to correct both liver and muscle are needed.

Bone Mineral Density in Patients with Hepatic Glycogen Storage Diseases

The association between bone mineral density (BMD) and hepatic glycogen storage diseases (GSDs) is still unclear. To evaluate the BMD of patients with GSD I, IIIa and IXα, a cross-sectional study was performed, including 23 patients (GSD Ia = 13, Ib = 5, IIIa = 2 and IXα = 3; median age = 11.9 years; IQ = 10.9–20.1) who underwent a dual-energy X-ray absorptiometry (DXA). Osteocalcin (OC, n = 18), procollagen type 1 N-terminal propeptide (P1NP, n = 19), collagen type 1 C-terminal telopeptide (CTX, n = 18) and 25-OH Vitamin D (n = 23) were also measured. The participants completed a 3-day food diary (n = 20). Low BMD was defined as a Z-score ≤ −2.0. All participants were receiving uncooked cornstarch (median dosage = 6.3 g/kg/day) at inclusion, and 11 (47.8%) presented good metabolic control. Three (13%) patients (GSD Ia = 1, with poor metabolic control; IIIa = 2, both with high CPK levels) had a BMD ≤ −2.0. CTX, OC and P1NP correlated negatively with body weight and age. 25-OH Vitamin D concentration was decreased in seven (30.4%) patients. Our data suggest that patients with hepatic GSDs may have low BMD, especially in the presence of muscular involvement and poor metabolic control. Systematic nutritional monitoring of these patients is essential.

Orthopaedic Manifestations of Inborn Errors of Metabolism

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Inborn errors of metabolism are disorders of carbohydrate, amino acid, organic acid, or purine and pyrimidine metabolism; disorders of fatty acid oxidation; disorders of metal metabolism; and lysosomal storage defects that can cause metabolic derangements that have secondary musculoskeletal effects.

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Orthopaedic surgeons should be aware that patients with inborn errors of metabolism may be at high risk for spasticity, which may cause joint subluxations, scoliosis, and contractures, as well as poor bone quality, which is caused by malnutrition or disordered bone growth.

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Multidisciplinary care and follow-up are important to identify musculoskeletal problems in a timely manner in order to provide effective treatment.

Biomarkers in Glycogen Storage Diseases: An Update

Glycogen storage diseases (GSDs) are a group of 19 hereditary diseases caused by a lack of one or more enzymes involved in the synthesis or degradation of glycogen and are characterized by deposits or abnormal types of glycogen in tissues. Their frequency is very low and they are considered rare diseases. Except for X-linked type IX, the different types are inherited in an autosomal recessive pattern. In this study we reviewed the literature from 1977 to 2020 concerning GSDs, biomarkers, and metabolic imbalances in the symptoms of some GSDs. Most of the reported studies were performed with very few patients. Classification of emerging biomarkers between different types of diseases (hepatics GSDs, McArdle and PDs and other possible biomarkers) was done for better understanding. Calprotectin for hepatics GSDs and urinary glucose tetrasaccharide for Pompe disease have been approved for clinical use, and most of the markers mentioned in this review only need clinical validation, as a final step for their routine use. Most of the possible biomarkers are implied in hepatocellular adenomas, cardiomyopathies, in malfunction of skeletal muscle, in growth retardation, neutropenia, osteopenia and bowel inflammation. However, a few markers have lost interest due to a great variability of results, which is the case of biotinidase, actin alpha 2, smooth muscle, aorta and fibroblast growth factor receptor 4. This is the first review published on emerging biomarkers with a potential application to GSDs.

Role of Metabolism in Bone Development and Homeostasis

Carbohydrates, fats, and proteins are the underlying energy sources for animals and are catabolized through specific biochemical cascades involving numerous enzymes. The catabolites and metabolites in these metabolic pathways are crucial for many cellular functions; therefore, an imbalance and/or dysregulation of these pathways causes cellular dysfunction, resulting in various metabolic diseases. Bone, a highly mineralized organ that serves as a skeleton of the body, undergoes continuous active turnover, which is required for the maintenance of healthy bony components through the deposition and resorption of bone matrix and minerals. This highly coordinated event is regulated throughout life by bone cells such as osteoblasts, osteoclasts, and osteocytes, and requires synchronized activities from different metabolic pathways. Here, we aim to provide a comprehensive review of the cellular metabolism involved in bone development and homeostasis, as revealed by mouse genetic studies.

Glycogen storage disease type 1a is associated with disturbed vitamin A metabolism and elevated serum retinol levels

Glycogen storage disease type 1a (GSD Ia) is an inborn error of metabolism caused by mutations in the G6PC gene, encoding the catalytic subunit of glucose-6-phosphatase. Early symptoms include severe fasting intolerance, failure to thrive and hepatomegaly, biochemically associated with nonketotic hypoglycemia, fasting hyperlactidemia, hyperuricemia and hyperlipidemia. Dietary management is the cornerstone of treatment aiming at maintaining euglycemia, prevention of secondary metabolic perturbations and long-term complications, including liver (hepatocellular adenomas and carcinomas), kidney and bone disease (hypovitaminosis D and osteoporosis). As impaired vitamin A homeostasis also associates with similar symptoms and is coordinated by the liver, we here analysed whether vitamin A metabolism is affected in GSD Ia patients and liver-specific G6pc^−/− knock-out mice. Serum levels of retinol and retinol binding protein 4 (RBP4) were significantly increased in both GSD Ia patients and L-G6pc^−/− mice. In contrast, hepatic retinol levels were significantly reduced in L-G6pc^−/− mice, while hepatic retinyl palmitate (vitamin A storage form) and RBP4 levels were not altered. Transcript and protein analyses indicate an enhanced production of retinol and reduced conversion the retinoic acids (unchanged LRAT, Pnpla2/ATGL and Pnpla3 up, Cyp26a1 down) in L-G6pc^−/− mice. Aberrant expression of genes involved in vitamin A metabolism was associated with reduced basal messenger RNA levels of markers of inflammation (Cd68, Tnfα, Nos2, Il-6) and fibrosis (Col1a1, Acta2, Tgfβ, Timp1) in livers of L-G6pc^−/− mice. In conclusion, GSD Ia is associated with elevated serum retinol and RBP4 levels, which may contribute to disease symptoms, including osteoporosis and hepatic steatosis.

Reduced bone mineral density in glycogen storage disease type III: evidence for a possible connection between metabolic imbalance and bone homeostasis

INTRODUCTION

Glycogen storage disease type III (GSDIII) is an inborn error of carbohydrate metabolism caused by deficient activity of glycogen debranching enzyme (GDE). It is characterized by liver, cardiac muscle and skeletal muscle involvement. The presence of systemic complications such as growth retardation, ovarian polycystosis, diabetes mellitus and osteopenia/osteoporosis has been reported. The pathogenesis of osteopenia/osteoporosis is still unclear.

OBJECTIVES

The aim of the current study was to evaluate the bone mineral density (BMD) in GSDIII patients and the role of metabolic and endocrine factors and physical activity on bone status.

METHODS

Nine GSDIII patients were enrolled (age 2-20years) and compared to eighteen age and sex matched controls. BMD was evaluated by Dual-emission-X-ray absorptiometry (DXA) and Quantitative ultrasound (QUS). Clinical and biochemical parameters of endocrine system function and bone metabolism were analyzed. Serum levels of the metabolic control markers were evaluated. Physical activity was evaluated by administering the International Physical Activity Questionnaire (IPAQ).

RESULTS

GSDIII patients showed reduced BMD detected at both DXA and QUS, decreased serum levels of IGF-1, free IGF-1, insulin, calcitonin, osteocalcin (OC) and increased serum levels of C-terminal cross-linking telopeptide of type I collagen (CTX). IGF-1 serum levels inversely correlated with AST and ALT serum levels. DXA Z-score inversely correlated with cholesterol and triglycerides serum levels and directly correlated with IGF-1/IGFBP3 molar ratio. No difference in physical activity was observed between GSDIII patients and controls.

DISCUSSION

Our data confirm the presence of reduced BMD in GSDIII. On the basis of the results, we hypothesized that metabolic imbalance could be the key factor leading to osteopenia, acting through different mechanisms: chronic hyperlipidemia, reduced IGF-1, Insulin and OC serum levels. Thus, the mechanism of osteopenia/osteoporosis in GSDIII is probably multifactorial and we speculate on the factors involved in its pathogenesis.

Diagnosis and management of glycogen storage disease type I: a practice guideline of the American College of Medical Genetics and Genomics

PURPOSE

Glycogen storage disease type I (GSD I) is a rare disease of variable clinical severity that primarily affects the liver and kidney. It is caused by deficient activity of the glucose 6-phosphatase enzyme (GSD Ia) or a deficiency in the microsomal transport proteins for glucose 6-phosphate (GSD Ib), resulting in excessive accumulation of glycogen and fat in the liver, kidney, and intestinal mucosa. Patients with GSD I have a wide spectrum of clinical manifestations, including hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, and growth retardation. Individuals with GSD type Ia typically have symptoms related to hypoglycemia in infancy when the interval between feedings is extended to 3–4 hours. Other manifestations of the disease vary in age of onset, rate of disease progression, and severity. In addition, patients with type Ib have neutropenia, impaired neutrophil function, and inflammatory bowel disease. This guideline for the management of GSD I was developed as an educational resource for health-care providers to facilitate prompt, accurate diagnosis and appropriate management of patients.

METHODS

A national group of experts in various aspects of GSD I met to review the evidence base from the scientific literature and provided their expert opinions. Consensus was developed in each area of diagnosis, treatment, and management.

RESULTS

This management guideline specifically addresses evaluation and diagnosis across multiple organ systems (hepatic, kidney, gastrointestinal/nutrition, hematologic, cardiovascular, reproductive) involved in GSD I. Conditions to consider in the differential diagnosis stemming from presenting features and diagnostic algorithms are discussed. Aspects of diagnostic evaluation and nutritional and medical management, including care coordination, genetic counseling, hepatic and renal transplantation, and prenatal diagnosis, are also addressed.

CONCLUSION

A guideline that facilitates accurate diagnosis and optimal management of patients with GSD I was developed. This guideline helps health-care providers recognize patients with all forms of GSD I, expedite diagnosis, and minimize adverse sequelae from delayed diagnosis and inappropriate management. It also helps to identify gaps in scientific knowledge that exist today and suggests future studies.

Bone mineral density in glycogen storage disease type Ia and Ib

Purpose:The aim of this study was to characterize the pathogenesis of low bone mineral density in glycogen storage disease type Ia and Ib.Methods:A retrospective chart review performed at the University of Florida Glycogen Storage Disease Program included patients with glycogen storage disease type Ia and Ib for whom dual-energy X-ray absorptiometry analysis was performed. A Z-score less than -2 SD was considered low. Analysis for association of bone mineral density with age, gender, presence of complications, mean triglyceride and 25-hydroxyvitamin D concentrations, erythrocyte sedimentation rate, duration of granulocyte colony-stimulating factor therapy, and history of corticosteroid use was performed.Results:In glycogen storage disease Ia, 23/42 patients (55%) had low bone mineral density. Low bone mineral density was associated with other disease complications (P = 0.02) and lower mean serum 25-hydroxyvitamin D concentration (P = 0.03). There was a nonsignificant trend toward lower mean triglyceride concentration in the normal bone mineral density group (P = 0.1).In patients with glycogen storage disease type Ib, 8/12 (66.7%) had low bone mineral density. We did not detect an association with duration of granulocyte colony-stimulating factor therapy (P = 0.68), mean triglyceride level (P = 0.267), erythrocyte sedimentation rate (P = 0.3), or 25-hydroxyvitamin D (P = 0.63) concentration, and there was no evidence that corticosteroid therapy was associated with lower bone mineral density (P = 1).Conclusion:In glycogen storage disease type Ia, bone mineral density is associated with other complications and 25-hydroxyvitamin D status. In glycogen storage disease type Ib, bone mineral density was not associated with any covariates analyzed, suggesting multifactorial etiology or reflecting a small sample.Genet Med advance online publication 5 April 2012.

Congenital and acquired neutropenias consensus guidelines on therapy and follow-up in childhood from the Neutropenia Committee of the Marrow Failure Syndrome Group of the AIEOP (Associazione Italiana Emato-Oncologia Pediatrica)

The management of congenital and acquired neutropenias presents some differences according to the type of the disease. Treatment with recombinant human granulocyte-colony stimulating factor (G-CSF) is not standardized and scanty data are available on the best schedule to apply. The frequency and the type of longitudinal controls in patients affected with neutropenias are not usually discussed in the literature. The Neutropenia Committee of the Marrow Failure Syndrome Group (MFSG) of the Associazione Italiana di Emato-Oncologia Pediatrica (AIEOP) elaborated this document following design and methodology formerly approved by the AIEOP board. The panel of experts reviewed the literature on the topic and participated in a conference producing a document that includes recommendations on neutropenia treatment and timing of follow-up.

Hypovitaminosis D in glycogen storage disease type I

Glycogen storage disease type I (GSD I) is caused by inherited defects of the glucose 6-phosphatase complex, resulting in fasting hypoglycemia, lactic acidosis, hyperuricemia and hyperlipidemia. Sixteen out of 26 (61.5%) GSD I patients in our study had suboptimal levels (<30 ng/ml) of 25-hydroxyvitamin-D (25(OH)D) despite supplementation of vitamin D and/or vitamin D + calcium based on WHO standards in 24/26 (92.3%) patients. The restrictive nature of the GSD I diet, metabolic derangements and intestinal malabsorption seen in GSD I are possible reasons for the observed hypovitaminosis D. Our results suggest that measurement of 25(OH)D should be considered in the routine evaluation of GSD I patients.

Nutritional therapy for glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of inherited disorders characterized by enzyme defects that affect the glycogen synthesis and degradation cycle, classified according to the enzyme deficiency and the affected tissue. The understanding of GSD has increased in recent decades, and nutritional management of some GSDs has allowed better control of hypoglycemia and metabolic complications. However, growth failure and liver, renal, and other complications are frequent problems in the long-term outcome. Hypoglycemia is the main biochemical consequence of GSD type I and some of the other GSDs. The basis of dietary therapy is nutritional manipulation to prevent hypoglycemia and improve metabolic dysfunction, with the use of continuous nocturnal intragastric feeding or cornstarch therapy at night and foods rich in starches with low concentrations of galactose and fructose during the day and to prevent hypoglycemia during the night.

A high activity index of stearoyl-CoA desaturase is associated with increased risk of fracture in men

The activity index of stearoyl-CoA desaturase (SCD), a key enzyme in lipogenesis, was associated with increased risk of fracture in a longitudinal population-based cohort of men. This indicates that elevated levels of endogenous lipogenesis increase the risk of fracture and suggest a role for saturated fat in the pathogenesis of osteoporosis.

INTRODUCTION

Osteoblasts and marrow adipocytes are derived from a common mesenchymal progenitor, and experimental studies have indicated that increased adipogenesis can occur at the expense of osteoblasts, leading to bone loss. Stearoyl-CoA desaturase (SCD) converts saturated to monounsaturated fatty acids and is a key enzyme in lipogenesis.

METHODS

Analysis was performed in a population-based, longitudinal cohort study of men (n = 2009). A product-to-precursor index (palmitoleic acid/palmitic acid) was used to estimate SCD activity in fasting serum analyzed in samples obtained at enrollment at age 50 years. Fractures were documented in 422 men during 35 years of follow-up. Cox regression analysis was used to determine the risk of fracture according to SCD activity index.

RESULTS

The risk of fracture was highest among men with the highest levels of SCD activity index. Multivariable analysis of the risk of fracture in the highest quintile as compared to the lowest one showed that the rate ratio was 1.71 (95% CI 1.26-2.33) for any fracture, with an estimated population attributable risk of 15%. The risk was further increased within the highest quintile.

CONCLUSIONS

Our results indicate that elevated levels of endogenous lipogenesis increase the risk of fracture and suggest a role for saturated fat in the pathogenesis of osteoporosis.

Reduction in bone mineral density in glycogenosis type III may be due to a mixed muscle and bone deficit

Glycogen storage disease type III (GSD III; OMIM 232400) is an autosomal recessive deficiency of the glycogen debrancher enzyme, amylo-1,6-glucosidase (EC 3.2.1.33). Patients with other hepatic glycogenoses are known to have reduced bone mineral content (BMC) and to be at consequent risk of fractures. They have key metabolic differences from GSD III patients, however. This study examines bone density and metabolism in 15 GSD III patients (6 female) from childhood to adulthood (aged 10-34 years). The results demonstrate that patients with GSD III have low bone mass at all skeletal sites compared with healthy individuals of the same age and sex, with a significant proportion (40-64%) having BMD > 2 standard deviations below the mean for whole body and lumbar spine. The deficiency seems to be attributable to a mixed muscle andbone deficit. Lower bone mass was found at all sites for GSD IIIa patients (combined liver and muscle defect) compared with GSD IIIb patients (liver only defect).

CONCLUSION

Patients with GSD III have significantly abnormal bone mass, placing them at increased risk of potential fracture. The underlying mechanism is probably multifactorial with contributions from abnormal muscle physiology, abnormal metabolic milieu and altered nutrition affecting micronutrient intake. Therapies need to address all these factors to be successful.

11β-Hydroxysteroid Dehydrogenase Type 1 Regulation by Intracellular Glucose 6-Phosphate Provides Evidence for a Novel Link between Glucose Metabolism and Hypothalamo-Pituitary-Adrenal Axis Function

Microsomal glucose-6-phosphatase-alpha (G6Pase-alpha) and glucose 6-phosphate transporter (G6PT) work together to increase blood glucose concentrations by performing the terminal step in both glycogenolysis and gluconeogenesis. Deficiency of the G6PT in liver gives rise to glycogen storage disease type 1b (GSD1b), whereas deficiency of G6Pase-alpha leads to GSD1a. G6Pase-alpha shares its substrate (glucose 6-phosphate; G6P) with hexose-6-phosphate-dehydrogenase (H6PDH), a microsomal enzyme that regenerates NADPH within the endoplasmic reticulum lumen, thereby conferring reductase activity upon 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). 11beta-HSD1 interconverts hormonally active C11beta-hydroxy steroids (cortisol in humans and corticosterone in rodents) to inactive C11-oxo steroids (cortisone and 11-dehydrocorticosterone, respectively). In vivo reductase activity predominates, generating active glucocorticoid. We hypothesized that substrate (G6P) availability to H6PDH in patients with GSD1b and GSD1a will decrease or increase 11beta-HSD1 reductase activity, respectively. We investigated 11beta-HSD1 activity in GSD1b and GSD1a mice and in two patients with GSD1b and five patients diagnosed with GSD1a. We confirmed our hypothesis by assessing 11beta-HSD1 in vivo and in vitro, revealing a significant decrease in reductase activity in GSD1b animals and patients, whereas GSD1a patients showed a marked increase in activity. The cellular trafficking of G6P therefore directly regulates 11beta-HSD1 reductase activity and provides a novel link between glucose metabolism and function of the hypothalamo-pituitary-adrenal axis.

Glycogen storage diseases: New perspectives

Glycogen storage diseases (GSD) are inherited metabolic disorders of glycogen metabolism. Different hormones, including insulin, glucagon, and cortisol regulate the relationship of glycolysis, gluconeogenesis and glycogen synthesis. The overall GSD incidence is estimated 1 case per 20000-43000 live births. There are over 12 types and they are classified based on the enzyme deficiency and the affected tissue. Disorders of glycogen degradation may affect primarily the liver, the muscle, or both. Type Ia involves the liver, kidney and intestine (and Ib also leukocytes), and the clinical manifestations are hepatomegaly, failure to thrive, hypoglycemia, hyperlactatemia, hyperuricemia and hyperlipidemia. Type IIIa involves both the liver and muscle, and IIIb solely the liver. The liver symptoms generally improve with age. Type IV usually presents in the first year of life, with hepatomegaly and growth retardation. The disease in general is progressive to cirrhosis. Type VI and IX are a heterogeneous group of diseases caused by a deficiency of the liver phosphorylase and phosphorylase kinase system. There is no hyperuricemia or hyperlactatemia. Type XI is characterized by hepatic glycogenosis and renal Fanconi syndrome. Type II is a prototype of inborn lysosomal storage diseases and involves many organs but primarily the muscle. Types V and VII involve only the muscle.