Effect of dietary interventions in the maintenance of normoglycaemia in glycogen storage disease type 1a: a systematic review and meta-analysis

Intestinal microbiota composition of children with glycogen storage Type I patients

AIM

Dietary therapy of glycogen storage disease I (GSD I) is based on frequent feeding, with a high intake of complex carbohydrates (supplied by uncooked cornstarch), restriction of sugars, and a lower amount of lipids. There is limited information about the dietary regimen in patients with GSD, which might affect the intestinal luminal pH and microbiota composition. The aim of this study to investigate the intestinal microbiota composition in patients with GSD receiving diet treatment.

METHOD

Twelve patients who were followed up with GSD I after the diagnosis receiving diet therapy and 11 healthy children have been enrolled. Intestinal microbiota composition was evaluated by 16 s rRNA gene sequencing.

RESULTS

A significant difference was found for beta-diversity between the GSD group and controls. A significantly lower abundance of Firmicutes and higher abundance of Actinobacteria was found in GSD group compared to the controls. Akkermansia, Pseudoalteromonas, Uruburella, and Castellaniella were dominant in the GSD patients at the genus level, while Faecalibacterium, Bacterioides, Gemmiger, Parabacteroides in the control group. At species level, Faecalibacterium prausnitzii decreased, and Akkermansia muciniphila were dominant in children with GSD.

DISCUSSION

There is a substantial change in the composition of the gut microbiota, reduction of F. prausnitzii and an increase of A. muciniphila in children with GSD receiving consumption of uncooked cornstarch. Alterations of the intestinal microbiota might be related with the disease itself or dietary restrictions in patients with GSD, however, in certain condition, dysbiosis can negatively affect the course and make it difficult to control the disease.

Severe perioperative lactic acidosis in a pediatric patient with glycogen storage disease type Ia: a case report

BACKGROUND

Glycogen storage disease (GSD) is a group of rare inherited metabolic disorders caused by enzyme deficiencies in glycogen catabolism. GSD type Ia is a congenital deficiency of the enzyme responsible for the final step in glucose production by glycolysis, resulting in impaired carbohydrate metabolism.

CASE PRESENTATION

A 14-year-old boy with GSD type Ia was scheduled for a maxillary cystectomy under general anesthesia. He was taking oral sugars such as uncooked cornstarch regularly to prevent hypoglycemia. Perioperatively, glucose was administered via the peripheral vein for fasting; however, severe lactic acidosis occurred. He also developed hypercapnia because of intraoperative poor ventilation caused by hepatomegaly.

CONCLUSIONS

We experienced a child with GSD type Ia who developed severe lactic acidosis despite continuous glucose infusion. Further studies are required to determine appropriate perioperative management for patients with GSD, including fasting glucose administration.

Estimation of Health Utility Scores for Glycogen Storage Disease Type Ia

BACKGROUND

Glycogen Storage Disease Type Ia (GSDIa) is a rare genetic metabolic disorder characterized by hypoglycemia, hepatomegaly, growth failure, and possible seizures/death. Patients frequently consume cornstarch to maintain blood glucose. Evidence demonstrating the impact of GSDIa on health-related quality of life (HRQoL) is lacking. This study aims to understand the burden of GSDIa by obtaining utility values for economic appraisals.

METHODS

A targeted literature review and interviews with experts (n = 4) and caregivers (n = 4) informed the development of health state vignettes describing different GSDIa severities by age and level of hypothetical treatment (i.e., gene therapy) response. Health states reflecting caregivers' experiences were also developed. A convenience sample of the UK general public completed a time trade-off (TTO) exercise. Scores conceptually varied from 0 (dead) to 1 (full health). States were also rated using a visual analog scale (VAS) and the EQ-5D-5L. Data were descriptively summarized.

RESULTS

One hundred participants completed the exercise (male: 48%; mean age: 42 years). Scores were lowest for the adolescent pre-treatment state (TTO = 0.38). Large increments in HRQoL were observed for the response (adult: TTO = 0.86; child: TTO = 0.84) and complete response (adult and child: TTO = 0.94) hypothetical treatment response states. Caregiver values were lowest for the pre-treatment state (TTO = 0.57) and highest for the complete response state (TTO = 0.95). VAS and EQ-5D-5L scores followed a similar pattern.

CONCLUSION

This study found an HRQoL burden on GSDIa patients and caregivers, with potential large improvement from a hypothetical treatment. These findings may be useful for families, clinicians, regulatory agencies, and in therapy economic evaluations.

Amnio acid substitution at position 298 of human glucose-6 phosphatase-α significantly impacts its stability in mammalian cells

Glucose-6-phosphatase-α (G6Pase-α) catalyzes the hydrolysis of glucose-6-phosphate to glucose and functions as a key regulator in maintaining blood glucose homeostasis. Deficiency in G6Pase-α causes glycogen storage disease 1a (GSD1a), an inherited disorder characterized by life-threatening hypoglycemia and other long-term complications. We have developed a potential mRNA-based therapy for GSD1a and demonstrated that a human G6Pase-α (hG6Pase-α) variant harboring a single serine (S) to cysteine (C) substitution at the amino acid site 298 (S298C) had > twofold increase in protein expression, resulting in improved in vivo efficacy. Here, we sought to investigate the mechanisms contributing to the increased expression of the S298C variant. Mutagenesis of hG6Pase-α identified distinct protein variants at the 298 amino acid position with substantial reduction in protein expression in cultured cells. Kinetic analysis of expression and subcellular localization in mammalian cells, combined with cell-free in vitro translation assays, revealed that altered protein expression stemmed from differences in cellular protein stability rather than biosynthetic rates. Site-specific mutagenesis studies targeting other cysteines of the hG6Pase-α S298C variant suggest the observed improvements in stability are not due to additional disulfide bond formation. The glycosylation at Asparagine (N)-96 is critical in maintaining enzymatic activity and mutations at position 298 mainly affected glycosylated forms of hG6Pase-α. Finally, proteasome inhibition by lactacystin improved expression levels of unstable hG6Pase-α variants. Taken together, these data uncover a critical role for a single amino acid substitution impacting the stability of G6Pase-α and provide insights into the molecular genetics of GSD1a and protein engineering for therapeutic development.

Studies on glycogen storage disease type 1a animal models: a brief perspective

Glycogen storage disease type 1 (GSD1) is a rare hereditary monogenic disease characterized by the disturbed glucose metabolism. The most widespread variant of GSD1 is GSD1a, which is a deficiency of glucose-6-phosphatase-ɑ. Glucose-6-phosphatase-ɑ is expressed only in liver, kidney, and intestine, and these organs are primarily affected by its deficiency, and long-term complications of GSD1a include hepatic tumors and chronic liver disease. This article is a brief overview of existing animal models for GSD1a, from the first mouse model of 1996 to modern CRISPR/Cas9-generated ones. First whole-body murine models demonstrated exact metabolic symptoms of GSD1a, but the animals did not survive weaning. The protocol for glucose treatment allowed prolonged survival of affected animals, but long-term complications, such as hepatic tumorigenesis, could not be investigated. Next, organ-specific knockout models were developed, and most of the metabolic research was performed on liver glucose-6-phosphate-deficient mice. Naturally occuring mutation was also discovered in dogs. All these models are widely used to study GSD1a from metabolic and physiological standpoints and to develop possible treatments involving gene therapy. Research performed using these models helped elucidate the role of glycogen and lipid accumulation, hypoxia, mitochondrial dysfunction, and autophagy impairment in long-term complications of GSD1a, including hepatic tumorigenesis. Recently, gene replacement therapy and genome editing were tested on described models, and some of the developed approaches have reached clinical trials.

Diet therapy in patients with rare diseases: a scoping review

BACKGROUND

This scoping review presents existing research evidence regarding diet therapy in patients with rare diseases (RDs).

METHODS

Using the five-stage scoping review framework proposed by Arksey, O'Malley and Levac, we searched the published literature in PubMed, Web of Science, Royal Society of Chemistry, China National Knowledge Infrastructure, VIP Database and Wan Fang Database from January 2010 to November 2022. We selected diet therapy studies on 121 RDs, as categorised by the National Health Commission of China in 2018. Charts for research analysis were developed and used to categorise the data.

RESULTS

We ultimately included 34 diet therapy studies from 19 countries and territories for 10 RDs and 3 RD groups. RD diet therapy studies have mainly focused on inborn errors of metabolism (92.3%) and are common in Western countries. Most studies focused on diet therapy methods for RDs (44%). In addition, 29% of studies included diet therapy management, 15% included guidelines for diet therapy and 12% included the impact of diet therapy on patients.

CONCLUSIONS

Current diet therapies for RDs lack specificity and present with limited characteristics. Therefore, it is necessary to expand the scope and depth of future research and explore evidence-based recommendations and new diet therapies focused on patient needs and family support to provide a reference for improving the efficacy and safety of diet therapies for RDs.

Glycogen storage disease type Ia misdiagnosed as multiple acyl-coenzyme A dehydrogenase deficiency by mass spectrometry

OBJECTIVE

To report a case of glycogen storage disease (GSD) type Ia misdiagnosed as multiple acyl-coenzyme a dehydrogenase deficiency (MADD) by mass spectrometry.

METHODS

A 7 months old boy was admitted to our hospital for elevated transaminase levels lasting more than 1 month. His blood biochemistry showed hypoglycemia, metabolic acidosis, hyperlipidemia, elevated lactate and uric acid, elevated alanine amino transferase (ALT), aspartate amino transaminase (AST) and gamma-glutamyl transferase (GGT). Mass spectrometry analysis of blood and urine showed elevated blood acylcarnitines and dicarboxylic aciduria, indicating multiple acyl-coenzyme A dehydrogenase deficiency. Sanger sequencing of all exons of glucose-6-phosphatase (G6Pase) and electronic transfer flavoprotein dehydrogenase (ETFDH) was performed for the patient and his parents.

RESULTS

Coding and flanking sequences of the G6Pase gene detected two heterozygous single base substitutions in the boy. One variant was in exon 1 (c.209G > A), Which was also detected in the father. Another was in exon 5 (c.648G > T), which was detected in the mother. Coding and flanking sequences of the ETFDH gene revealed no pathogenic/likely pathogenic variants in the boy.

CONCLUSION

GSD Ia can manifest elevated blood acyl carnitines and dicarboxylic aciduria which were the typical clinical manifestations of MADD. So the patient with clinical manifestations similar to MADD is in need of differential diagnosis for GSD Ia. Genetic testing is helpful to confirming the diagnosis of inherited metabolic diseases.

Investigating paediatric hypoglycaemia: Dynamic studies at a tertiary paediatric hospital

AIM

Paediatric hypoglycaemia often requires specific investigations to determine aetiology. Samples from the time of hypoglycaemia may not be available and a diagnostic fasting test may be required. Additionally, fasting studies can determine safe fasting intervals and prolonged oral glucose challenges can assess hypoglycaemia due to abnormal post-prandial glucose handling. This audit reviewed the current utility and yield of fasting studies, prolonged oral glucose challenges and starch loads.

METHODS

Retrospective audit of clinical record to determine purpose and outcome of tests performed at a Tertiary Paediatric Endocrine/Metabolic Testing Unit in Sydney, Australia, from 2013 to 2018 inclusive.

RESULTS

One hundred and thirty-eight children (aged 3 weeks-17 years) underwent 170 tests: 122 fasting studies, 20 five-hour OGTTs, 22 uncooked corn starch loads and six modified waxy maize starch (Glycosade) loads. The majority were for diagnostic purposes (n = 113, 66%), with 57 (34%) to guide management in patients with known diagnoses. Following diagnostic studies, 35 (31%) patients received a pathological diagnosis, the most common of which (n = 19, 17%) was accelerated starvation. Hypoglycaemia developed in n = 15/113 (13%) during the diagnostic studies. Management studies helped determine length of safe fast, adjustment of medication or diet and document resolution of pathology.

CONCLUSION

Fasting studies remain a safe and effective method to assist with diagnoses, confirm or exclude pathological causes of childhood hypoglycaemia and to guide management of known diagnoses in the paediatric population.

mRNA therapy restores euglycemia and prevents liver tumors in murine model of glycogen storage disease

Glycogen Storage Disease 1a (GSD1a) is a rare, inherited metabolic disorder caused by deficiency of glucose 6-phosphatase (G6Pase-α). G6Pase-α is critical for maintaining interprandial euglycemia. GSD1a patients exhibit life-threatening hypoglycemia and long-term liver complications including hepatocellular adenomas (HCAs) and carcinomas (HCCs). There is no treatment for GSD1a and the current standard-of-care for managing hypoglycemia (Glycosade®/modified cornstarch) fails to prevent HCA/HCC risk. Therapeutic modalities such as enzyme replacement therapy and gene therapy are not ideal options for patients due to challenges in drug-delivery, efficacy, and safety. To develop a new treatment for GSD1a capable of addressing both the life-threatening hypoglycemia and HCA/HCC risk, we encapsulated engineered mRNAs encoding human G6Pase-α in lipid nanoparticles. We demonstrate the efficacy and safety of our approach in a preclinical murine model that phenotypically resembles the human condition, thus presenting a potential therapy that could have a significant therapeutic impact on the treatment of GSD1a.

ANTHROPOMETRIC AND DIETARY ASSESSMENT OF PATIENTS WITH GLYCOGENOSIS TYPE I

Objective:

To perform anthropometric and dietary evaluation of patients with glycogenosis type Ia and Ib.

Methods:

This cross-sectional study is composed of a sample of 11 patients with glycogenosis divided into two subgroups according to the classification of glycogenosis (type Ia=5 and type Ib=6), aged between 4 and 20 years. The analyzed anthropometric variables were weight, height, body mass index, and measures of lean and fat body mass, which were compared with reference values. For dietary assessment, a food frequency questionnaire was used to calculate energy and macronutrients intake as well as the amount of raw cornstarch consumed. Mann-Whitney U test and Fisher’s exact test were performed, considering a significance level of 5%.

Results:

Patients ingested raw cornstarch in the amount of 0.49 to 1.34 g/kg/dose at a frequency of six times a day, which is lower than recommended (1.75-2.50 g/kg/dose, four times a day). The amount of energy intake was, on average, 50% higher than energy requirements; however, carbohydrate intake was below the adequacy percentage in 5/11 patients. Short stature was found in 4/10 patients; obesity, in 3/11; and muscle mass deficit, in 7/11. There were no statistical differences between the subgroups.

Conclusions:

In patients with glycogenosis type I, there was deficit in growth and muscle mass, but no differences were found between the subgroups (Ia and Ib). Although the diet did not exceed the adequacy of carbohydrates, about 1/3 of the patients presented obesity, probably due to higher energy intake.

Uncooked cornstarch for the prevention of hypoglycemic events

Hypoglycemia is a pathological condition characterized by a low plasma glucose concentration associated with typical autonomic and/or neuroglycopenic symptoms, and resolution of these symptoms with carbohydrate consumption. Hypoglycemia is quite common in clinical practice, particularly in insulin-treated patients with diabetes and in other inherited or acquired conditions involving the regulation of glucose metabolism. Beyond symptoms that might strongly affect the quality of life, hypoglycemia can lead to short- and long-term detrimental consequences for health. Hypoglycemia can be prevented by appropriate changes in dietary habits or by relevant modifications of the drug treatment. Several dietary approaches based on the intake of various carbohydrate foods have been tested for hypoglycemia prevention; among them uncooked cornstarch (UCS) has demonstrated a great efficacy. In this narrative review, we have summarized the current evidence on the UCS usefulness in some conditions characterized by high hypoglycemic risk, focusing on some inherited diseases -i.e. glycogen storage diseases and other rare disorders - and acquired conditions such as type 1 diabetes, postprandial hypoglycemia consequent to esophageal-gastric or bariatric surgery, and insulin autoimmune syndrome. We also considered the possible role of UCS during endurance exercise performance. Lastly, we have discussed the dose requirement, the side effects, the limitations of UCS use, and the plausible mechanisms by which UCS could prevent hypoglycemia.

Hepatic Glycogenoses Among Children-Clinical and Biochemical Characterization: Single-Center Study

BACKGROUND

Glycogen storage disease (GSD) is typified by early morning seizures. Absence of this results in delayed diagnosis, especially the non-GSD 1 group. Data are limited to few patients with unclear outcome.

OBJECTIVES

1. Study the common presentation and types of GSD. 2. Study the clinical and biochemical outcome. 3. Review genetic mutations.

METHODS

Observational study from May 2016-April 2019 at metabolic clinic at our center.

RESULTS

Total of 30 patients were diagnosed with GSD. Ten were excluded-Fanconi-Bickel (3) and <4 months follow-up (7). Data were analyzed for 20 patients (16 males). Mean age at presentation was 4.3 yrs. All had hepatomegaly, 90% had short stature, and 40% had early morning seizures. Mean follow-up was 22 months. There was a statistically significant improvement in metabolic parameters on treatment (mean)-fasting glucose from 50.4 to 79.5 mg/dl, SGPT from 416 to 199 U/L. Lipid profile showed reduction in triglycerides (318-225 mg/dl) but minimal increase in cholesterol (178-188 mg/dl). Mean weight centile improved from 14.1 to 20.3 and height centile from 2.3 to 7.9. Genetic testing confirmed types VI (3), III (3), IXa (1), IXc (1), and Ia (1). Liver biopsy confirmed GSD in 15/20. All were managed with uncooked corn starch. In addition, omega-3 fatty acid was used in 8/20 and high protein diet in 2 with GSD type III.

CONCLUSION

Awareness of GSD needs to improve among pediatricians and hepatologists. The most common symptoms are asymptomatic hepatomegaly and short stature. Dietary therapy with uncooked corn starch remains mainstay of treatment. Mixed hyperlipidemia is difficult to control despite good metabolic improvement. Role of omega-3 fatty acid needs to be explored further. Genetic mutation analysis can assist with tailoring treatment and should get precedence over liver biopsy.

Predominance of the c.648G > T G6PC gene mutation and late complications in Korean patients with glycogen storage disease type Ia

BACKGROUND

Glycogen storage disease (GSD) Ia, caused by mutations in the glucose-6-phosphatase (G6PC) gene, is characterized by hepatomegaly, hypoglycemia, lactic acidosis, dyslipidemia, and hyperuricemia. This study aimed to investigate clinical and molecular features and late complications in Korean patients with GSD Ia.

RESULTS

Fifty-four Korean patients (33 males and 21 females) from 47 unrelated families, who were diagnosed with GSD Ia, based on genetic and biochemical data, between 1999 and 2017, were included in this study. The median age at diagnosis was 3.9 years (range: 5 months to 42 years), and the follow-up period was 8.0 ± 6.8 years. Most patients presented with hepatomegaly during infancy, but hypoglycemic symptoms were not predominant. Genetic analysis showed that all the patients had at least one c.648G > T allele. Homozygous c.648G > T mutations in the G6PC gene were identified in 34 families (72.3%), and compound heterozygotes with c.648G > T were found in the other families. The allele frequency of c.648G > T was 86.2% (81/94), and p.F51S, p.R83H, p.G122D, p.Y128*, p.G222R, and p.T255A were identified. Of 26 adult patients, 14 had multiple hepatic adenomas, and two were diagnosed with hepatocellular carcinoma. Thirteen patients showed renal complications, and seven patients presented gout, despite preventive allopurinol treatment. Twelve patients had osteoporosis, and two patients had pulmonary hypertension. The final heights were 157.9 cm (standard deviation score: - 3.1) in males and 157.8 cm (standard deviation score: - 0.6) in females.

CONCLUSION

In our Korean patients with GSD Ia, the most common mutation in the G6PC gene was c.648G > T, suggesting a founder effect. Because of only mild hypoglycemia, the patients tended to be diagnosed late. Thus, adult patients with GSD Ia eventually developed diverse and serious complications, which indicates a need for careful monitoring and proper management of this disease.

Use of waxy maize heat modified starch in the treatment of children between 2 and 5 years with glycogen storage disease type I: A retrospective study

Background

Glycogen storage disease type I (GSDI) is caused by deficiency of the enzyme glucose-6-phosphatase or glucose-6-phosphate transporter. Mainstay of treatment is provision of uncooked cornstarch (and/or continuous nocturnal pump feed (CNPF) to maintain normoglycemia). Waxy maize heat modified starch (WMHMS) is another treatment option to maintain normoglycemia overnight. Our objective was to describe our experience treating children 2–5 years of age with GSDI using WMHMS overnight.

Method

This is a retrospective case series review (n = 5) comparing the overnight feeding regimen and biochemical control one year before and after nocturnal WMHMS therapy. The WMHMS trial, in which blood glucose and lactate levels were monitored hourly, is reported in detail.

Results

Most patients successfully transitioned to nocturnal WMHMS feeds. These patients had stable glucose and lactate throughout the overnight period, permitting a fasting period of 6.5–8 h overnight. Within the time period studied, WMHMS appeared to have improved overnight control of blood glucose levels with fewer reported episodes of hypoglycemia compared to CNPF.

Conclusion

WMHMS can be an effective substitute treatment to achieve stable nocturnal glucose control in children younger than five years of age. A larger multicenter prospective study is recommended to establish stronger evidence of the efficacy and safety of using WMHMS in treatment of young children with GSDI.

Current and Emerging Agents for the Treatment of Hypoglycemia in Patients with Congenital Hyperinsulinism

Congenital hyperinsulinism (CHI) is the most common cause of persistent hypoglycmia in neonatles and children. The inappropriate secretion of insulin by the pancreatic β-cells produces recurrent hypoglycemia, which can lead to severe and permanent brain damage. CHI results from mutations in different genes that play a role in the insulin secretion pathway, and each differs in their responsiveness to medical treatment. Currently, the only available approved treatment for hyperinsulinism is diazoxide. Patients unresponsive to diazoxide may benefit from specialized evaluation including genetic testing and 18F-DOPA PET to identify those with focal forms of CHI. The focal forms can be cured by selective pancreatectomy, but the management of diazoxide-unresponsive diffuse CHI is a real therapeutic challenge. Current off-label therapies include intravenous glucagon, octreotide and long-acting somatostatin analogs; however, they are often insufficient, and a 98% pancreatectomy or continuous feeds may be required. For the first time in over 40 years, new drugs are being developed, but none have made it to market yet. In this review, we will discuss current on-label and off-label drugs and review the currently available data on the novel drugs under development.

Hepatic glycogen storage diseases: pathogenesis, clinical symptoms and therapeutic management

Glycogen storage diseases (GSDs) are genetically determined metabolic diseases that cause disorders of glycogen metabolism in the body. Due to the enzymatic defect at some stage of glycogenolysis/glycogenesis, excess glycogen or its pathologic forms are stored in the body tissues. The first symptoms of the disease usually appear during the first months of life and are thus the domain of pediatricians. Due to the fairly wide access of the authors to unpublished materials and research, as well as direct contact with the GSD patients, the article addresses the problem of actual diagnostic procedures for patients with the suspected diseases. Knowledge and awareness of the problem among physicians seem insufficient, and research on the diagnosis and treatment of GSD is still ongoing, resulting in a heterogeneous GSD typology and a changing way of its diagnosis and treatment.

Safety issues associated with dietary management in patients with hepatic glycogen storage disease

INTRODUCTION

Hepatic glycogen storage diseases (GSDs) are a group of inherited disorders of carbohydrate metabolism for which dietary management is the cornerstone. Safety and acute complications associated with dietary management have been poorly documented. We hypothesized that safety issues and complications associated with dietary management are prevalent amongst patients with these ultra-rare disorders.

METHODS

A questionnaire was developed consisting of 40 questions and was distributed via eight GSD patient organizations from multiple countries. Respondents were (caregivers of) patients with self-reported hepatic GSD.

RESULTS

249 GSD patients from 26 countries responded with a median age of 14.8 years (range: 0.5-66.1). Although management was considered safe by 71% of patients, 51% reported at least one acute complication associated with dietary management, with a total number of 425 reported complications. Most frequently reported causes were: not waking up by an alarm clock (n = 70), forgetting a meal (n = 57) and infections (n = 43). Most frequently reported complications were: hypoglycemia (n = 112), hospital admissions (n = 79) and drowsiness (n = 74). Most complications occurred before the age of 12 years (82%; 637/774 total number of reported events) and during night time (63%; 340/536). Only 61% (152/249) of the GSD patients reported using a written emergency protocol.

CONCLUSIONS

Safety issues and complications associated with dietary management are prevalently reported by (caregivers of) 249 GSD patients. A discrepancy has been observed between the patient's perspective on safety of dietary management and occurrence of complications as a result of dietary management.

The Physiopathological Role of the Exchangers Belonging to the SLC37 Family

The human SLC37 gene family includes four proteins SLC37A1-4, localized in the endoplasmic reticulum (ER) membrane. They have been grouped into the SLC37 family due to their sequence homology to the bacterial organophosphate/phosphate (Pi) antiporter. SLC37A1-3 are the less characterized isoforms. SLC37A1 and SLC37A2 are Pi-linked glucose-6-phosphate (G6P) antiporters, catalyzing both homologous (Pi/Pi) and heterologous (G6P/Pi) exchanges, whereas SLC37A3 transport properties remain to be clarified. Furthermore, SLC37A1 is highly homologous to the bacterial glycerol 3-phosphate permeases, so it is supposed to transport also glycerol-3-phosphate. The physiological role of SLC37A1-3 is yet to be further investigated. SLC37A1 seems to be required for lipid biosynthesis in cancer cell lines, SLC37A2 has been proposed as a vitamin D and a phospho-progesterone receptor target gene, while mutations in the SLC37A3 gene appear to be associated with congenital hyperinsulinism of infancy. SLC37A4, also known as glucose-6-phosphate translocase (G6PT), transports G6P from the cytoplasm into the ER lumen, working in complex with either glucose-6-phosphatase-α (G6Pase-α) or G6Pase-β to hydrolyze intraluminal G6P to Pi and glucose. G6PT and G6Pase-β are ubiquitously expressed, whereas G6Pase-α is specifically expressed in the liver, kidney and intestine. G6PT/G6Pase-α complex activity regulates fasting blood glucose levels, whereas G6PT/G6Pase-β is required for neutrophil functions. G6PT deficiency is responsible for glycogen storage disease type Ib (GSD-Ib), an autosomal recessive disorder associated with both defective metabolic and myeloid phenotypes. Several kinds of mutations have been identified in the SLC37A4 gene, affecting G6PT function. An increased autoimmunity risk for GSD-Ib patients has also been reported, moreover, SLC37A4 seems to be involved in autophagy.

Inborn Errors of Metabolism with Hypoglycemia: Glycogen Storage Diseases and Inherited Disorders of Gluconeogenesis

Although hyperinsulinism is the predominant inherited cause of hypoglycemia in the newborn period, inborn errors of metabolism are the primary etiologies after 1 month of age. Disorders of carbohydrate metabolism often present with hypoglycemia when fasting occurs. The presentation, diagnosis, and management of the hepatic glycogen storage diseases and disorders of gluconeogenesis are reviewed.

Clinical practice guidelines for congenital hyperinsulinism

Congenital hyperinsulinism is a rare condition, and following recent advances in diagnosis and treatment, it was considered necessary to formulate evidence-based clinical practice guidelines reflecting the most recent progress, to guide the practice of neonatologists, pediatric endocrinologists, general pediatricians, and pediatric surgeons. These guidelines cover a range of aspects, including general features of congenital hyperinsulinism, diagnostic criteria and tools for diagnosis, first- and second-line medical treatment, criteria for and details of surgical treatment, and future perspectives. These guidelines were generated as a collaborative effort between The Japanese Society for Pediatric Endocrinology and The Japanese Society of Pediatric Surgeons, and followed the official procedures of guideline generation to identify important clinical questions, perform a systematic literature review (April 2016), assess the evidence level of each paper, formulate the guidelines, and obtain public comments.

Molecular genetic analysis and phenotypic characteristics of a consanguineous family with glycogen storage disease type Ia

Glycogen storage disease type‑Ia (GSD‑Ia) is a rare autosomal recessive disease caused by a mutation in the gene encoding glucose‑6‑phosphate‑α (G6PC). The present study reported the case of a 3‑month‑old female Chinese patient with GSD‑Ia born to consanguineous parents. The aim of the present study was to identify the precise mutation of the G6PC gene associated with this family and to describe the phenotypic characteristics of the patient. A comprehensive examination was performed on the patient, including physical examination, vein blood gas analysis, abdominal sonography and biochemical analyses. In addition, gene sequencing was performed on the coding region of the G6PC gene to identify the mutation. The patient was diagnosed with GSD‑Ia and a G6PC missense mutation of c.518T>C (p.L173P) located in a highly conserved area was identified. The mutation is in a non‑helical region of the protein, which previous studies have suggested should result in a lesser effect on G6PC enzymatic activity and milder phenotypic characteristics compared with mutations located in helical regions. However, the severity of the disease phenotype in the subject of the present study was inconsistent with that predicted from her genotype. The patient suffered from serious hypoglycemia, lactic acidosis, increased triglycerides, hepatic dysfunction, clear hepatomegaly and nephromegaly. The incidence of the p.L173P mutation may be relatively high in the Chinese population. Knowledge of the various phenotypic presentations of the p.L173P mutation may beneficial for future investigations.

Glycogen metabolism in humans

In the human body, glycogen is a branched polymer of glucose stored mainly in the liver and the skeletal muscle that supplies glucose to the blood stream during fasting periods and to the muscle cells during muscle contraction. Glycogen has been identified in other tissues such as brain, heart, kidney, adipose tissue, and erythrocytes, but glycogen function in these tissues is mostly unknown. Glycogen synthesis requires a series of reactions that include glucose entrance into the cell through transporters, phosphorylation of glucose to glucose 6-phosphate, isomerization to glucose 1-phosphate, and formation of uridine 5'-diphosphate-glucose, which is the direct glucose donor for glycogen synthesis. Glycogenin catalyzes the formation of a short glucose polymer that is extended by the action of glycogen synthase. Glycogen branching enzyme introduces branch points in the glycogen particle at even intervals. Laforin and malin are proteins involved in glycogen assembly but their specific function remains elusive in humans. Glycogen is accumulated in the liver primarily during the postprandial period and in the skeletal muscle predominantly after exercise. In the cytosol, glycogen breakdown or glycogenolysis is carried out by two enzymes, glycogen phosphorylase which releases glucose 1-phosphate from the linear chains of glycogen, and glycogen debranching enzyme which untangles the branch points. In the lysosomes, glycogen degradation is catalyzed by α-glucosidase. The glucose 6-phosphatase system catalyzes the dephosphorylation of glucose 6-phosphate to glucose, a necessary step for free glucose to leave the cell. Mutations in the genes encoding the enzymes involved in glycogen metabolism cause glycogen storage diseases.

Defining 'nutraceuticals': neither nutritious nor pharmaceutical

There are widespread inconsistencies and contradictions in the many published definitions of 'nutraceuticals' and 'functional foods', demonstrating wholesale uncertainty about what they actually are. Furthermore, in a 2014 lecture, the inventor of the term 'nutraceutical', confessing that nutraceuticals do not work, said that 'the quest to demonstrate whether … long-term supplementation [with nutraceuticals] can prevent serious diseases … has come to an end'. Definitions of 'nutraceuticals' and related terms, still widely used, should therefore be explored systematically. There are no internationally agreed definitions of 'nutraceuticals' and 'functional foods', or of similar terms, such as 'health foods', or of terms related to herbal products, which are sometimes referred to as 'nutraceuticals', compounding the confusion. 'Nutraceuticals' and 'functional foods' are vague, nondiscriminatory, unhelpful terms; the evidence suggests that they should be abandoned in favour of more precise terms. The term 'dietary supplement' is widely used to designate formulations that are also called 'nutraceuticals' but it would be better restricted to individual compounds used to treat or prevent deficiencies. 'Fortified foods', sometimes called 'designer foods', are foods to which compounds of proven therapeutic or preventive efficacy (e.g. folic acid) have been added. Other terms, such as 'food', 'foodstuffs', 'eat', 'drink', and 'nutrition', are well defined, as are 'medicinal products' and 'pharmaceutical formulations'. Dietary regimens, such as Mediterranean or nitrate-rich diets or vegetarianism, can affect health. A dietary regimen of this kind can be defined as a programme of food, of a defined kind and/or quantity, prescribed or adopted for the restoration or preservation of health.

Alternative nighttime nutrition regimens in glycogen storage disease type I: a controlled crossover study

BACKGROUND

Traditional approaches for nighttime glycemic control in glycogen storage disease type I (GSDI) include continuous tube feeding, or ingestion of uncooked corn starch (CS) at bedtime. A modified corn starch (MCS) has been shown to prolong euglycemia in some patients. The aim of this study was to evaluate whether stable nighttime glucose control can be achieved with other types of slowly digested carbohydrates in adult GSDI patients.

METHODS

In this cross-over study, nocturnal glucose control and fasting times were assessed with three different nocturnal nutrition regimens in five patients, using continuous glucose monitoring (CGMS) in an outpatient everyday life setting. For each patient, continuous glucose profiles were measured after ingestion of (1) CS, (2) MCS or (3) a pasta meal at bedtime, during 5 to 6 consecutive nights for each regimen.

RESULTS

Stable nocturnal glucose control was achieved for all patients with a pasta meal, with a mean duration of glycemia >3.5 mmol/l of 7.6 h (range 5.7-10.8), and >4 mmol/l of 7 h (5.2-9.2), similar to CS and MCS. Fasting glucose before breakfast on workdays (after 7.1 ± 0.8 h) was not significantly different between the three interventions (CS 4.1 ± 0.5 mmol/l, MCS 4.6 ± 0.7 mmol/l, pasta 4.3 ± 0.9 mmol/l). During prolonged fasting on weekends, longer duration of normoglycemia was achieved with CS or MCS than with pasta.

CONCLUSION

Consumption of cooked pasta is a suitable and more palatable alternative to uncooked corn starch to achieve nighttime glucose control in adult patients with GSDI.

Inherited Metabolic Disorders: Aspects of Chronic Nutrition Management

The introduction of newborn screening and the development of new therapies have led to an expanding population of patients with inherited metabolic disorders, and these patients are now entering adulthood. Dietary therapy is the mainstay of treatment for many of these disorders, and thus, trained metabolic dietitians are critical members of the multidisciplinary team required for management of such patients. The main goals of dietary therapy in inborn errors of metabolism are the maintenance of normal growth and development while limiting offending metabolites and providing deficient products. Typically, the offending metabolite is either significantly reduced or removed completely from the diet and then reintroduced in small quantities until blood levels are within the normal range. Such treatment is required in infancy, childhood, and adulthood and requires careful monitoring of micronutrient and macronutrient intake throughout the life span. The goal of this review is to highlight the basic principles of chronic nutrition management of the inborn errors of protein, carbohydrate, and fat metabolism.

Hepatic glycogen storage disorders: what have we learned in recent years?

PURPOSE OF REVIEW

Glycogen storage disorders (GSDs) are inborn errors of metabolism with abnormal storage or utilization of glycogen. The present review focuses on recent advances in hepatic GSD types I, III and VI/IX, with emphasis on clinical aspects and treatment.

RECENT FINDINGS

Evidence accumulates that poor metabolic control is a risk factor for the development of long-term complications, such as liver adenomas, low bone density/osteoporosis, and kidney disease in GSD I. However, mechanisms leading to these complications remain poorly understood and are being investigated. Molecular causes underlying neutropenia and neutrophil dysfunction in GSD I have been elucidated. Case series provide new insights into the natural course and outcome of GSD types VI and IX. For GSD III, a high protein/fat diet has been reported to improve (cardio)myopathy, but the beneficial effect of this dietary concept on muscle and liver disease manifestations needs to be further established in prospective studies.

SUMMARY

Although further knowledge has been gained regarding pathophysiology, disease course, treatment, and complications of hepatic GSDs, more controlled prospective studies are needed to assess effects of different dietary and medical treatment options on long-term outcome and quality of life.

Type I glycogen storage diseases: disorders of the glucose-6-phosphatase/glucose-6-phosphate transporter complexes

Disorders of the glucose-6-phosphatase (G6Pase)/glucose-6-phosphate transporter (G6PT) complexes consist of three subtypes: glycogen storage disease type Ia (GSD-Ia), deficient in the liver/kidney/intestine-restricted G6Pase-α (or G6PC); GSD-Ib, deficient in a ubiquitously expressed G6PT (or SLC37A4); and G6Pase-β deficiency or severe congenital neutropenia syndrome type 4 (SCN4), deficient in the ubiquitously expressed G6Pase-β (or G6PC3). G6Pase-α and G6Pase-β are glucose-6-phosphate (G6P) hydrolases with active sites lying inside the endoplasmic reticulum (ER) lumen and as such are dependent upon the G6PT to translocate G6P from the cytoplasm into the lumen. The tissue expression profiles of the G6Pase enzymes dictate the disease's phenotype. A functional G6Pase-α/G6PT complex maintains interprandial glucose homeostasis, while a functional G6Pase-β/G6PT complex maintains neutrophil/macrophage energy homeostasis and functionality. G6Pase-β deficiency is not a glycogen storage disease but biochemically it is a GSD-I related syndrome (GSD-Irs). GSD-Ia and GSD-Ib patients manifest a common metabolic phenotype of impaired blood glucose homeostasis not shared by GSD-Irs. GSD-Ib and GSD-Irs patients manifest a common myeloid phenotype of neutropenia and neutrophil/macrophage dysfunction not shared by GSD-Ia. While a disruption of the activity of the G6Pase-α/G6PT complex readily explains why GSD-Ia and GSD-Ib patients exhibit impaired glucose homeostasis, the basis for neutropenia and myeloid dysfunction in GSD-Ib and GSD-Irs are only now starting to be understood. Animal models of all three disorders are now available and are being exploited to both delineate the disease more precisely and develop new treatment approaches, including gene therapy.

Secondary hypertriglyceridemia in children and adolescents

Secondary dyslipidemia with predominant hypertriglyceridemia may occur as a consequence of both common and rare causes. After accounting for obesity and associated insulin resistance, clinicians should carefully consider other contributing factors and conditions. Genetic background and causative factors prevail during gestation, infancy, and childhood and continue in adults. Elevations in triglyceride (TG) are associated with transfer of TG to high-density lipoprotein (HDL) and low-density lipoprotein (LDL) resulting in lipolysis, HDL degradation, and formation of atherogenic LDL particles. Defining and treating the underlying cause is the first step toward restoring the lipids and lipoproteins to normal, especially in cases with severe hypertriglyceridemia, who are at risk for acute pancreatitis. Disorders involving the liver, kidney, endocrine, and immune systems and medications need to be considered. Rare diseases such as lipodystrophy and glycogen storage disease are particularly challenging, and there have been promising new developments. Treatment depends on the severity; prevention of acute pancreatitis being a priority in severe cases and lifestyle modification being a foundation for general management followed by targeting TG and predictors of coronary artery disease such as LDL cholesterol and non-HDL cholesterol, when they exceed cutpoints.

Lipids in hepatic glycogen storage diseases: pathophysiology, monitoring of dietary management and future directions

Hepatic glycogen storage diseases (GSD) underscore the intimate relationship between carbohydrate and lipid metabolism. The hyperlipidemias in hepatic GSD reflect perturbed intracellular metabolism, providing biomarkers in blood to monitor dietary management. In different types of GSD, hyperlipidemias are of a different origin. Hypertriglyceridemia is most prominent in GSD type Ia and associated with long-term outcome morbidity, like pancreatitis and hepatic adenomas. In the ketotic subtypes of GSD, hypertriglyceridemia reflects the age-dependent fasting intolerance, secondary lipolysis and increased mitochondrial fatty acid oxidation. The role of high protein diets is established for ketotic types of GSD, but non-traditional dietary interventions (like medium-chain triglycerides and the ketogenic diet) in hepatic GSD are still controversial and necessitate further studies. Patients with these rare inherited disorders of carbohydrate metabolism meet several criteria of the metabolic syndrome, therefore close monitoring for cardiovascular diseases in ageing GSD patients may be justified.

A pilot longitudinal study of the use of waxy maize heat modified starch in the treatment of adults with glycogen storage disease type I: a randomized double-blind cross-over study

Background

Uncooked corn-starch (UCCS) has been the mainstay of therapy for the hepatic glycogen storage diseases (GSD) but is not always effective. A new starch (WMHMS) has demonstrated a more favourable short-term metabolic profile.

Objective

To determine efficacy and safety of a new uncooked starch (WMHMS) compared to UCCS over 16 weeks treatment with each.

Method

A double-blind cross-over study of 10 adults (aged 16 – 38 years, six male) with GSD Ia and Ib. After an individualised fast, subjects were randomised to take a 50 g starch-load of either WMHMS or UCCS. Starch-loads terminated when blood glucose was < 3.0 mmol/L or the subject felt subjectively hypoglycaemic. Anonymous biochemical profiles were assessed by 2 investigators and a starch administration schedule recommended. Each starch was delivered in coded sachets and intake was monitored for the following 16 weeks. After a washout period, the protocol was repeated with the alternative product.

Results

4 subjects failed to establish therapy on the cross-over limb. Data from 7 paired starch load showed: longer median fasting duration with WMHMS (7.5 versus 5 hours; p = 0.023), slower decrease in the glucose curve (0.357 versus 0.632 mmol/hr p = 0.028) and less area under insulin curves for the first 4 hours (p = 0.03). Two of six subjects took 50% or less WMHMS compared to UCCS and one took more. Plasma triglycerides, cholesterol and uric acid were unchanged after each study phase.

Conclusion

WMHMS leads to significant reduction in insulin release and reduced starch use in some GSD patients.

Glycogen storage disease type I: clinical and laboratory profile

OBJECTIVES

To characterize the clinical, laboratory, and anthropometric profile of a sample of Brazilian patients with glycogen storage disease type I managed at an outpatient referral clinic for inborn errors of metabolism.

METHODS

This was a cross-sectional outpatient study based on a convenience sampling strategy. Data on diagnosis, management, anthropometric parameters, and follow-up were assessed.

RESULTS

Twenty-one patients were included (median age 10 years, range 1-25 years), all using uncooked cornstarch therapy. Median age at diagnosis was 7 months (range, 1-132 months), and 19 patients underwent liver biopsy for diagnostic confirmation. Overweight, short stature, hepatomegaly, and liver nodules were present in 16 of 21, four of 21, nine of 14, and three of 14 patients, respectively. A correlation was found between height-for-age and BMI-for-age Z-scores (r=0.561; p=0.008).

CONCLUSIONS

Diagnosis of glycogen storage disease type I is delayed in Brazil. Most patients undergo liver biopsy for diagnostic confirmation, even though the combination of a characteristic clinical presentation and molecular methods can provide a definitive diagnosis in a less invasive manner. Obesity is a side effect of cornstarch therapy, and appears to be associated with growth in these patients.