Glycogen storage diseases

Broadening the Phenotype and Genotype Spectrum of Glycogen Storage Disease by Unraveling Novel Variants in an Iranian Patient Cohort

Glycogen storage diseases (GSDs) are a group of rare inherited metabolic disorders characterized by clinical, locus, and allele heterogeneity. This study aims to investigate the phenotype and genotype spectrum of GSDs in a cohort of 14 families from Iran using whole-exome sequencing (WES) and variant analysis. WES was performed on 14 patients clinically suspected of GSDs. Variant analysis was performed to identify genetic variants associated with GSDs. A total of 13 variants were identified, including six novel variants, and seven previously reported pathogenic variants in genes such as AGL, G6PC, GAA, PYGL, PYGM, GBE1, SLC37A4, and PHKA2. Most types of GSDs observed in the cohort were associated with hepatomegaly, which was the most common clinical presentation. This study provides valuable insights into the phenotype and genotype spectrum of GSDs in a cohort of Iranian patients. The identification of novel variants adds to the growing body of knowledge regarding the genetic landscape of GSDs and has implications for genetic counseling and future therapeutic interventions. The diverse nature of GSDs underscores the need for comprehensive genetic testing methods to improve diagnostic accuracy. Continued research in this field will enhance our understanding of GSDs, ultimately leading to improved management and outcomes for individuals affected by these rare metabolic disorders.

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.

In vivo characterization of glycogen storage disease type III in a mouse model using glycoNOE MRI

PURPOSE

Glycogen storage disease type III (GSD III) is a rare inherited metabolic disease characterized by excessive accumulation of glycogen in liver, skeletal muscle, and heart. Currently, there are no widely available noninvasive methods to assess tissue glycogen levels and disease load. Here, we use glycogen nuclear Overhauser effect (glycoNOE) MRI to quantify hepatic glycogen levels in a mouse model of GSD III.

METHODS

Agl knockout mice (n = 13) and wild-type controls (n = 10) were scanned for liver glycogen content using glycoNOE MRI. All mice were fasted for 12 to 16 h before MRI scans. GlycoNOE signal was quantified by fitting the Z-spectrum using a four-pool Voigt lineshape model. Next, the fitted direct water saturation pool was removed and glycoNOE signal was estimated from the integral of the residual Z spectrum within -0.6 to -1.4 ppm. Glycogen concentration was also measured ex vivo using a biochemical assay.

RESULTS

GlycoNOE MRI clearly distinguished Agl knockout mice from wild-type controls, showing a statistically significant difference in glycoNOE signals in the livers across genotypes. There was a linear correlation between glycoNOE signal and glycogen concentration determined by the biochemical assay. The obtained glycoNOE maps of mouse livers also showed higher glycogen levels in Agl knockout mice compared to wild-type mice.

CONCLUSION

GlycoNOE MRI was used successfully as a noninvasive method to detect liver glycogen levels in mice, suggesting the potential of this method to be applied to assess glycogen storage diseases.

Report of an Iranian child with chronic abdominal pain and constipation diagnosed as glycogen storage disease type IX: a case report

BACKGROUND

Glycogen storage disease type IX is a rare disorder that can cause a wide variety of symptoms depending on the specific deficiency of the phosphorylase kinase enzyme and the organs it affects.

CASE PRESENTATION

A 4-and-a-half-year-old Caucasian girl was referred to our clinic with a liver biopsy report indicating a diagnosis of glycogen storage disease. Prior to being referred to our clinic, the patient had been under the care of pediatric gastroenterologists. The patient's initial symptoms included chronic abdominal pain, constipation, and elevated liver transaminase. With the help of the pediatric gastroenterologists, cholestasis, Wilson disease, and autoimmune hepatitis were ruled out. Given that glycogen storage diseases type I and type III are the most common, we initially managed the patient with frequent feedings and a diet that included complex carbohydrates such as a corn starch supplement and a lactose restriction. Following an unfavorable growth velocity and hepatomegaly during the follow-up period, genetic analysis was conducted, which revealed a novel mutation of the phosphorylase kinase regulatory subunit beta gene- a c.C412T (P.Q138x) mutation. As the diagnosis of glycogen storage disease type IX was confirmed, the treatment regimen was altered to a high protein diet (more than 2 g/kg/day) and a low fat diet.

CONCLUSION

Given the mild and varied clinical manifestations of glycogen storage disease type IX, it is possible for the diagnosis to be overlooked. It is important to consider glycogen storage disease type IX in children who present with unexplained hepatomegaly and elevated transaminase levels. Furthermore, due to the distinct management of glycogen storage disease type IX compared with glycogen storage disease type I and glycogen storage disease type III, genetic analysis is essential for an accurate diagnosis.

Comparative metabolomics analysis investigating the impact of melatonin-enriched diet on energy metabolism in the crayfish, Cherax destructor

Melatonin is a multifunctional bioactive molecule present in almost all organisms and has been gradually used in the aquaculture industry in recent years. Energy metabolism is an essential process for individuals to maintain their life activities; however, the process through which melatonin regulates energy metabolism in aquatic animals remains unclear. The present study aimed to conduct a comprehensive analysis of the regulatory mechanism of melatonin for energy metabolism in Cherax destructor by combining metabolomics analysis with the detection of the key substance content, enzymatic activity, and gene expression levels in the energy metabolism process after culturing with dietary melatonin supplementation for 8 weeks. Our results showed that dietary melatonin increased the content of glycogen, triglycerides, and free fatty acids; decreased lactate levels; and promoted the enzymatic activity of pyruvate kinase (PK), malate dehydrogenase (MDH), and acetyl-CoA carboxylase. The results of gene expression analysis showed that dietary melatonin also increased the expression levels of hexokinase, PK, MDH, lactate dehydrogenase, lipase, and fatty acid synthase genes. The results of metabolomics analysis showed that differentially expressed metabolites were significantly enriched in lysine degradation and glycerophospholipid metabolism. In conclusion, our study demonstrates that dietary melatonin increased oxidative phosphorylation, improved glucose utilization, and promoted storage of glycogen and lipids in C. destructor. These lipids are used not only for energy storage but also to maintain the structure and function of cell membranes. Our results further add to the understanding of the mechanisms of energy regulation by melatonin in crustaceans.

Glycogen-binding protein STBD1: Molecule and role in pathophysiology

Starch-binding domain-containing protein 1 (STBD1) is a glycogen-binding protein discovered in skeletal muscle gene differential expression that is pivotal to cellular energy metabolism. Recent studies have indicated that STBD1 is involved in many physiological processes, such as glycophagy, glycogen accumulation, and lipid droplet formation. Moreover, dysregulation of STBD1 causes multiple diseases, including cardiovascular disease, metabolic disease, and even cancer. Deletions and/or mutations in STBD1 promote tumorigenesis. Therefore, STBD1 has garnered considerable interest in the pathology community. In this review, we first summarized the current understanding of STBD1, including its structure, subcellular localization, tissue distribution, and biological functions. Next, we examined the roles and molecular mechanisms of STBD1 in related diseases. Based on available research, we discussed the novel function and future of STBD1, including its potential application as a therapeutic target in glycogen-related diseases. Given the significance of STBD1 in energy metabolism, an in-depth understanding of the protein is crucial for understanding physiological processes and developing therapeutic strategies for related diseases.

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.

Molecular, Biochemical, and Clinical Characterization of Thirteen Patients with Glycogen Storage Disease 1a in Malaysia

Background

Glycogen storage disease type 1a (GSD1a) is a rare autosomal recessive metabolic disorder characterized by hypoglycaemia, growth retardation, lactic acidosis, hepatomegaly, hyperlipidemia, and nephromegaly. GSD1a is caused by a mutation in the G6PC gene encoding glucose-6-phosphatase (G6Pase); an enzyme that catalyses the hydrolysis of glucose-6-phosphate (G6P) to phosphate and glucose.

Objective

To elaborate on the clinical findings, biochemical data, molecular genetic analysis, and short-term prognosis of 13 GSD1a patients in Malaysia.

Methods

The information about 13 clinically classified GSD1a patients was retrospectively studied. The G6PC mutation analysis was performed by PCR-DNA sequencing.

Results

Patients were presented with hepatomegaly (92%), hypoglycaemia (38%), poor weight gain (23%), and short stature (15%). Mutation analysis revealed nine heterozygous mutations; eight previously reported mutations (c.155 A > T, c.209 G > A, c.226 A > T, c.248 G > A, c.648 G > T, c.706 T > A, c.1022 T > A, c.262delG) and a novel mutation (c.325 T > C). The most common mutation found in Malaysian patients was c.648 G > T in ten patients (77%) of mostly Malay ethnicity, followed by c.248 G > A in 4 patients of Chinese ethnicity (30%). A novel missense mutation (c.325 T > C) was predicted to be disease-causing by various in silico software.

Conclusions

The establishment of G6PC molecular genetic testing will enable the detection of presymptomatic patients, assisting in genetic counselling while avoiding the invasive methods of liver biopsy.

Increased atherosclerosis in a mouse model of glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD Ia) is an inborn error of carbohydrate metabolism. Despite severe hyperlipidemia, GSD Ia patients show limited atherogenesis compared to age-and-gender matched controls. Employing a GSD Ia mouse model that resembles the severe hyperlipidemia in patients, we here found increased atherogenesis in GSD Ia. These data provide a rationale for investigating atherogenesis in GSD Ia in a larger patient cohort.

Two successful pregnancies and first use of empagliflozin during pregnancy in glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD Ib) is caused by biallelic variants in SLC37A4. GSD Ib is characterized by hepatomegaly, recurrent hypoglycemia, neutropenia, and neutrophil dysfunction. Only seven pregnancies in four women with GSD Ib have been reported so far. We report on two further successful pregnancies in two patients with GSD Ib. One of these pregnancies was managed with empagliflozin, an SGLT2 inhibitor, repurposed for the treatment of neutropenia in GSD Ib. Both pregnancies were unremarkable and resulted in healthy offspring. Gestational care and pre‐ and perinatal management in GSD Ib are challenging and require close interdisciplinary metabolic and obstetric monitoring. In our patient, the use of empagliflozin during pregnancy was successful in the prevention of neutropenic symptoms and infections and enabled good wound healing after Cesarean section, while no adverse effects were observed.

Diagnosis and follow-up of Glycogen Storage Disease (GSD) Type VI from the largest GSD center in China

Glycogen storage disease (GSD) type VI is a glycogenolysis disorder caused by variants of PYGL. Knowledge about this disease is limited because only approximately 50 cases have been reported. we investigated the clinical profiles, molecular diagnosis, and treatment outcomes in patients with gsd VI from 2000 to 2021. The main initial clinical features of this cohort include hepatomegaly, short stature, elevated liver transaminases, hypertriglyceridemia, fasting hypoglycemia, and hyperuricemia. After uncooked cornstarch treatment, the stature and biochemical parameters improved significantly (P < 0.05). However, hyperuricemia recurred in most patients during adolescence. Among the 56 GSD VI patients, 54 biallelic variants and two single allelic variants of PYGL were identified, of which 43 were novel. There were two hotspot variants, c.1621-258_2178-23del and c.2467C>T p.(Gln823*), mainly in patients from Southwest and South China. c.1621-258_2178-23del is a 3.6 kb deletion that results in an out-of-frame deletion r.1621_2177del and an in-frame deletion r.1621_2265del. Our data show for the first time that long-term monitoring of uric acid is recommended for older GSD VI patients. This study also broadens the variant spectrum of PYGL and indicates that there are two hot-spot variants in China. This article is protected by copyright. All rights reserved.

Multidisciplinary management of pregnancy and labour in a patient with glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD 1a) is a metabolic disorder caused by deficiency of an enzyme required for glycogen breakdown, causing hypoglycaemia and lactic acidosis. Metabolic derangements cause disease manifestations affecting the kidneys, liver and platelet function. Physiological changes in pregnancy worsen fasting intolerance and increase reliance on exogenous glucose to avoid lactic acidosis. Fetal macrosomia and declining respiratory function result in high rates of caesarean sections. We report the multidisciplinary team (MDT) management of a 25-year-old woman with GSD 1a in an unplanned pregnancy. Existing percutaneous endoscopic gastrostomy tube feeding, alongside high-calorie drinks and intravenous dextrose during labour, managed the risks of hypoglycaemia and lactic acidosis. Metabolic parameters were regularly monitored and fortnightly growth scans were assessed for macrosomia. Allopurinol was continued throughout the pregnancy to reduce the risk of hyperuricaemia. MDT management optimised maternal and fetal care throughout pregnancy and labour, resulting in a successful vaginal delivery.

PHKA2 variants expand the phenotype of phosphorylase B kinase deficiency to include patients with ketotic hypoglycemia only

Idiopathic ketotic hypoglycemia (IKH) is a diagnosis of exclusion with glycogen storage diseases (GSDs) as a differential diagnosis. GSD IXa presents with ketotic hypoglycemia (KH), hepatomegaly, and growth retardation due to PHKA2 variants. In our multicenter study, 12 children from eight families were diagnosed or suspected of IKH. Whole‐exome sequencing or targeted next‐generation sequencing panels were performed. We identified two known and three novel (likely) pathogenic PHKA2 variants, such as p.(Pro869Arg), p.(Pro498Leu), p.(Arg2Gly), p.(Arg860Trp), and p.(Val135Leu), respectively. Erythrocyte phosphorylase kinase activity in three patients with the novel variants p.(Arg2Gly) and p.(Arg860Trp) were 15%–20% of mean normal. One patient had short stature and intermittent mildly elevated aspartate aminotransferase, but no hepatomegaly. Family testing identified two asymptomatic children and 18 adult family members with one of the PHKA2 variants, of which 10 had KH symptoms in childhood and 8 had mild symptoms in adulthood. Our study expands the classical GSD IXa phenotype of PHKA2 missense variants to a continuum from seemingly asymptomatic carriers, over KH‐only with phosphorylase B kinase deficiency, to more or less complete classical GSD IXa. In contrast to typical IKH, which is confined to young children, KH may persist into adulthood in the KH‐only phenotype of PHKA2.

A triple-blinded crossover study to evaluate the short-term safety of sweet manioc starch for the treatment of glycogen storage disease type Ia

Background

Glycogen storage disease type 1a (GSD Ia) is characterized by severe fasting hypoglycemia. The clinical management includes the administration of uncooked cornstarch (UCCS). Although such a diet approach is effective in achieving euglycemia, its impact on the quality of life of patients should be considered. In vitro analyses suggest a longer release of glucose when using sweet manioc starch (SMS).

Methods

We compared the efficacy and safety of the administration of SMS and UCCS during a short-fasting challenge in patients with GSD Ia in a randomized, triple-blind, phase I/II, cross-over study. GSD Ia patients aged ≥ 16 years and treated with UCCS were enrolled. Participants were hospitalized for two consecutive nights, receiving UCCS or SMS in each night. After the administration of the starches, glucose, lactate and insulin levels were measured in 1-h interval throughout the hospitalization period. The procedures were interrupted after 10 h of fasting or in a hypoglycemic episode (< 3.88 mmol/L).

Results

Eleven individuals (mean age: 21.6 ± 4.3 years; all presenting body mass index > 25 kg/m²) participated in the study. The average fasting period was 8.2 ± 2.0 h for SMS and 7.7 ± 2.3 h for UCCS (p = 0.04). SMS maintained euglycemia for a greater period over UCCS. Increased lactate concentrations were detected even in absence of hypoglycemia, not being influenced by the different starches investigated (p = 0.17). No significant difference was found in total cholesterol, HDL, triglycerides and uric acid levels in both arms. None of the patients showed severe adverse events.

Conclusions

SMS appears to be non-inferior to UCCS in the maintenance of euglycemia, thus emerging as a promising alternative to the treatment of GSD Ia.

A novel gene therapy for neurodegenerative Lafora disease via EPM2A-loaded DLinDMA lipoplexes

Aim: To develop novel cationic liposomes as a nonviral gene delivery vector for the treatment of rare diseases, such as Lafora disease - a neurodegenerative epilepsy. Materials & methods: DLinDMA and DOTAP liposomes were formulated and characterized for the delivery of gene encoding laforin and expression of functional protein in HEK293 and neuroblastoma cells. Results: Liposomes with cationic lipids DLinDMA and DOTAP showed good physicochemical characteristics. Nanosized DLinDMA liposomes demonstrated desired transfection efficiency, negligible hemolysis and minimal cytotoxicity. Western blotting confirmed successful expression and glucan phosphatase assay demonstrated the biological activity of laforin. Conclusion: Our study is a novel preclinical effort in formulating cationic lipoplexes containing plasmid DNA for the therapy of rare genetic diseases such as Lafora disease.

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.

A Noncoding Variant Near PPP1R3B Promotes Liver Glycogen Storage and MetS, but Protects Against Myocardial Infarction

CONTEXT

Glycogen storage diseases are rare. Increased glycogen in the liver results in increased attenuation.

OBJECTIVE

Investigate the association and function of a noncoding region associated with liver attenuation but not histologic nonalcoholic fatty liver disease.

DESIGN

Genetics of Obesity-associated Liver Disease Consortium.

SETTING

Population-based.

MAIN OUTCOME

Computed tomography measured liver attenuation.

RESULTS

Carriers of rs4841132-A (frequency 2%-19%) do not show increased hepatic steatosis; they have increased liver attenuation indicative of increased glycogen deposition. rs4841132 falls in a noncoding RNA LOC157273 ~190 kb upstream of PPP1R3B. We demonstrate that rs4841132-A increases PPP1R3B through a cis genetic effect. Using CRISPR/Cas9 we engineered a 105-bp deletion including rs4841132-A in human hepatocarcinoma cells that increases PPP1R3B, decreases LOC157273, and increases glycogen perfectly mirroring the human disease. Overexpression of PPP1R3B or knockdown of LOC157273 increased glycogen but did not result in decreased LOC157273 or increased PPP1R3B, respectively, suggesting that the effects may not all occur via affecting RNA levels. Based on electronic health record (EHR) data, rs4841132-A associates with all components of the metabolic syndrome (MetS). However, rs4841132-A associated with decreased low-density lipoprotein (LDL) cholesterol and risk for myocardial infarction (MI). A metabolic signature for rs4841132-A includes increased glycine, lactate, triglycerides, and decreased acetoacetate and beta-hydroxybutyrate.

CONCLUSIONS

These results show that rs4841132-A promotes a hepatic glycogen storage disease by increasing PPP1R3B and decreasing LOC157273. rs4841132-A promotes glycogen accumulation and development of MetS but lowers LDL cholesterol and risk for MI. These results suggest that elevated hepatic glycogen is one cause of MetS that does not invariably promote MI.

Neurological Characteristics of Pediatric Glycogen Storage Disease

Glycogen storage diseases (GSD) encompass a group of rare inherited diseases due dysfunction of glycogen metabolism. Hypoglycemia is the most common primary manifestation of GSD, and disturbances in glucose metabolism can cause neurological damage. The aims of this study were to first investigate the metabolic, genetic, and neurological profiles of children with GSD, and to test the hypothesis whether GSD type I would have greater neurological impact than GSD type IX. A cross-sectional study was conducted with 12 children diagnosed with GSD [Types: Ia (n=5); 1, Ib (n=1); 4, IXa (n=5); and 1, IXb (n=1)]. Genetic testing was conducted for the following genes using multigene panel analysis. The biochemical data and magnetic resonance imaging of the brain presented by the patients were evaluated. The criteria of adequate metabolic control were adopted based on the European Study on Glycogen Storage Disease type I consensus. Pathogenic mutations were identified using multigene panel analyses. The mutations and clinical chronology were related to the disease course and neuroimaging findings. Adequate metabolic control was achieved in 67% of patients (GSD I, 43%; GSD IX, 100%). Fourteen different mutations were detected, and only two co-occurring mutations were observed across families (G6PC c.247C>T and c.1039C>T). Six previously unreported variants were identified (5 PHKA2; 1 PHKB). The proportion of GSD IX was higher in our cohort compared to other studies. Brain imaging abnormalities were more frequent among patients with GSD I, early-symptom onset, longer hospitalization, and inadequate metabolic control. The frequency of mutations was similar to that observed among the North American and European populations. None of the mutations observed in PHKA2 have been described previously. Therefore, current study reports six GSD variants previously unknown, and neurological consequences of GSD I. The principal neurological impact of GSD appeared to be related to inadequate metabolic control, especially hypoglycemia.

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.

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.

[Case of diagnostics of a rare form of glycogen disease]

Differential diagnosis of hypoglycemic syndrome remains an urgent problem in Pediatrics. In this article, a case of glycogen storage disease (BNG) type 0 is described in the boy, which is undoubtedly a rare pathology, which makes it difficult to diagnose this form of glycogenosis. In this description, the case of type 0 BNG is caused by a mutation in the GYS2 gene encoding the hepatic isoform of glycogen synthase. This form of the disease is usually asymptomatic in infancy. However, it can be suspected in the case when the refusal of night feeding causes certain difficulties due to the hungry ketotic hypoglycemia that occurs in the child. The first clinical symptoms appear in early childhood with the inclusion of a more varied diet in the child, increasing the intervals between meals. Symptoms of the disease are primarily caused by hypoglycemia. It should be noted that, despite the low levels of glycemia, most children do not have any mental development disorders, since the increase in the level of ketone bodies in the blood plasma provides the brain with an alternative source of energy.

A novel frameshift PHKA2 mutation in a family with glycogen storage disease type IXa: A first report in Vietnam and review of literature

BACKGROUND

Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders. Overlapping features between liver GSDs are a major challenge in the clinical diagnosis of them. Genetic testing can provide an early and accurate diagnosis of patients suspected with GSDs.

CASE PRESENTATION

In this study, we report two siblings born to healthy, non-consanguineous Vietnamese parents with hepatomegaly. The proband presented with hepatomegaly, normal spleen, elevated transaminases, without hypoglycemia, normal lactate dehydrogenase and creatine kinase. Liver biopsy revealed degeneration and swollen hepatocytes, suggesting a diagnosis with GSDs.

METHODS

Whole exome sequencing was applied to identify genetic variants in the proband. Variant validation and familial co-segregation analysis were examined using Sanger sequencing.

RESULTS

A novel frameshift duplication mutation c.3308_3312dupATGTC (p.L1105Mfs*11) of the PHKA2 gene was identified in the proband and his elder brother at the hemizygous state. This mutation was inherited from their mother. Their father and younger brother were normal genotype.

CONCLUSIONS

The two siblings were accurately diagnosed with GSD type XIa. This is the first case report of GSD type IXa in Vietnamese patients with a mutation in the PHKA2 gene. This finding may support for genetics diagnosis of unknown cause of hepatomegaly.

Discovery and Development of Small-Molecule Inhibitors of Glycogen Synthase

The overaccumulation of glycogen appears as a hallmark in various glycogen storage diseases (GSDs), including Pompe, Cori, Andersen, and Lafora disease. Accumulating evidence suggests that suppression of glycogen accumulation represents a potential therapeutic approach for treating these GSDs. Using a fluorescence polarization assay designed to screen for inhibitors of the key glycogen synthetic enzyme, glycogen synthase (GS), we identified a substituted imidazole, (rac)-2-methoxy-4-(1-(2-(1-methylpyrrolidin-2-yl)ethyl)-4-phenyl-1H-imidazol-5-yl)phenol (H23), as a first-in-class inhibitor for yeast GS 2 (yGsy2p). Data from X-ray crystallography at 2.85 Å, as well as kinetic data, revealed that H23 bound within the uridine diphosphate glucose binding pocket of yGsy2p. The high conservation of residues between human and yeast GS in direct contact with H23 informed the development of around 500 H23 analogs. These analogs produced a structure-activity relationship profile that led to the identification of a substituted pyrazole, 4-(4-(4-hydroxyphenyl)-3-(trifluoromethyl)-1H-pyrazol-5-yl)pyrogallol, with a 300-fold improved potency against human GS. These substituted pyrazoles possess a promising scaffold for drug development efforts targeting GS activity in GSDs associated with excess glycogen accumulation.

PRE AND POST-OPERATIVE OTORHINOLARYNGOLOGY SURGERY CARE IN PATIENTS WITH GLYCOGEN STORAGE DISEASE TYPE 1

OBJECTIVE

To discuss aspects of pre and post-operative otorhinolaryngology surgery in patients with glycogen storage disease type 1b.

CASE DESCRIPTION

Description of three clinical cases with probable glycogen storage disease type 1b who underwent otorhinolaryngology surgery, showing the importance of multidisciplinary interaction to avoid episodes of hypoglycemia.

COMMENTS

Patients with glycogen storage disease type 1b present recurrent infections, including the otorhinolaryngology affections. When there is an indication for surgical treatment, the caloric intake should be carefully followed in order to prevent hypoglycemia. The way to ensure this is to perform the pre and postoperative period in the hospital ward. In the postoperative period, it is important to make a slow transition between the intravenous and oral routes and not suspend the infusion of glucose during the surgical procedure. The cases illustrate the need for the interaction of the otorhinolaryngologic surgeon with the anesthesiologist, the pediatrician and the gastro-pediatrician in the management of these patients, avoiding hypoglycemic episodes.

Diagnosis and management of glycogen storage diseases type VI and IX: a clinical practice resource of the American College of Medical Genetics and Genomics (ACMG)

PURPOSE

Glycogen storage disease (GSD) types VI and IX are rare diseases of variable clinical severity affecting primarily the liver. GSD VI is caused by deficient activity of hepatic glycogen phosphorylase, an enzyme encoded by the PYGL gene. GSD IX is caused by deficient activity of phosphorylase kinase (PhK), the enzyme subunits of which are encoded by various genes: ɑ (PHKA1, PHKA2), β (PHKB), ɣ (PHKG1, PHKG2), and δ (CALM1, CALM2, CALM3). Glycogen storage disease types VI and IX have a wide spectrum of clinical manifestations and often cannot be distinguished from each other, or from other liver GSDs, on clinical presentation alone. Individuals with GSDs VI and IX can present with hepatomegaly with elevated serum transaminases, ketotic hypoglycemia, hyperlipidemia, and poor growth. This guideline for the management of GSDs VI and IX was developed as an educational resource for health-care providers to facilitate prompt and accurate diagnosis and appropriate management of patients.

METHODS

A national group of experts in various aspects of GSDs VI and IX met to review the limited evidence base from the scientific literature and provided their expert opinions. Consensus was developed in each area of diagnosis, treatment, and management. Evidence bases for these rare disorders are largely based on expert opinion, particularly when targeted therapeutics that have to clear the US Food and Drug Administration (FDA) remain unavailable.

RESULTS

This management guideline specifically addresses evaluation and diagnosis across multiple organ systems involved in GSDs VI and IX. Conditions to consider in a 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, and prenatal diagnosis are addressed.

CONCLUSION

A guideline that will facilitate the accurate diagnosis and optimal management of patients with GSDs VI and IX was developed. This guideline will help health-care providers recognize patients with GSDs VI and IX, expedite diagnosis, and minimize adverse sequelae from delayed diagnosis and inappropriate management. It will also help identify gaps in scientific knowledge that exist today and suggest future studies.

Feeding Difficulties and Orofacial Myofunctional Disorder in Patients with Hepatic Glycogen Storage Diseases

Hepatic glycogen storage diseases (GSDs) are inborn errors of metabolism whose dietary treatment involves uncooked cornstarch administration and restriction of simple carbohydrate intake. The prevalence of feeding difficulties (FDs) and orofacial myofunctional disorders (OMDs) in these patients is unknown.

OBJECTIVE

To ascertain the prevalence of FDs and OMDs in GSD.

METHODS

This was a cross-sectional, prospective study of 36 patients (19 males; median age, 12.0 years; range, 8.0-18.7 years) with confirmed diagnoses of GSD (type Ia = 22; Ib = 8; III = 2; IXa = 3; IXc = 1). All patients were being treated by medical geneticists and dietitians. Evaluation included a questionnaire for evaluation of feeding behavior, the orofacial myofunctional evaluation (AMIOFE), olfactory and taste performance (Sniffin' Sticks and Taste Strips tests), and facial anthropometry.

RESULTS

Nine (25%) patients had decreased olfactory perception, and four (11%) had decreased taste perception for all flavours. Eight patients (22.2%) had decreased perception for sour taste. Twenty-six patients (72.2%) had FD, and 18 (50%) had OMD. OMD was significantly associated with FD, tube feeding, selective intake, preference for fluid and semisolid foods, and mealtime stress (p < 0.05). Thirteen patients (36.1%) exhibited mouth or oronasal breathing, which was significantly associated with selective intake (p = 0.011) and not eating together with the rest of the family (p = 0.041). Lower swallowing and chewing scores were associated with FD and with specific issues related to eating behavior (p < 0.05).

CONCLUSION

There is a high prevalence of FDs and OMDs in patients with GSD. Eating behavior, decreased taste and smell perception, and orofacial myofunctional issues are associated with GSD.

Structure and Digestion of Common Complementary Food Starches

Starch is the major source of dietary glucose for rapid development of children. Starches from various crops naturally differ in molecular structures and properties. Cooking, processing, and storage may change their molecular properties and affect their digestibility and functionality. Starch digestion is affected by its susceptibility to α-amylase and α-glucosidase (maltase), and the susceptibility is determined by starch granule architecture and glucan structures, as well as the interaction between starch and other food components. Starch is given as a complementary feeding to young children in many cultures, and starch or modified starch, is used in special formulae of infant foods or supplements. Although indigestible starch does not provide much energy, it can benefit colonic health.

[Molecular and clinical characterization of Colombian patients suffering from type III glycogen storage disease]

INTRODUCTION

Type III glycogen storage disease (GSD III) is an autosomal recessive disorder in which a mutation in the AGL gene causes deficiency of the glycogen debranching enzyme. The disease is characterized by fasting hypoglycemia, hepatomegaly and progressive myopathy. Molecular analyses of AGL have indicated heterogeneity depending on ethnic groups. The full spectrum of AGL mutations in Colombia remains unclear.

OBJECTIVE

To describe the clinical and molecular characteristics of ten Colombian patients diagnosed with GSD III.

MATERIALS AND METHODS

We recruited ten Colombian children with a clinical and biochemical diagnosis of GSD III to undergo genetic testing. The full coding exons and the relevant exon-intron boundaries of the AGL underwent Sanger sequencing to identify mutation.

RESULTS

All patients had the classic phenotype of the GSD III. Genetic analysis revealed a mutation p.Arg910X in two patients. One patient had the mutation p.Glu1072AspfsX36, and one case showed a compound heterozygosity with p.Arg910X and p.Glu1072AspfsX36 mutations. We also detected the deletion of AGL gene 3, 4, 5, and 6 exons in three patients. The in silico studies predicted that these defects are pathogenic. No mutations were detected in the amplified regions in three patients.

CONCLUSION

We found mutations and deletions that explain the clinical phenotype of GSD III patients. This is the first report with a description of the clinical phenotype and the spectrum of AGL mutations in Colombian patients. This is important to provide appropriate prognosis and genetic counseling to the patient and their relatives.

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.

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.

Hypoinsulinaemic, hypoketotic hypoglycaemia due to mosaic genetic activation of PI3-kinase

OBJECTIVE

Genetic activation of the insulin signal-transducing kinase AKT2 causes syndromic hypoketotic hypoglycaemia without elevated insulin. Mosaic activating mutations in class 1A phospatidylinositol-3-kinase (PI3K), upstream from AKT2 in insulin signalling, are known to cause segmental overgrowth, but the metabolic consequences have not been systematically reported. We assess the metabolic phenotype of 22 patients with mosaic activating mutations affecting PI3K, thereby providing new insight into the metabolic function of this complex node in insulin signal transduction.

METHODS

Three patients with megalencephaly, diffuse asymmetric overgrowth, hypoketotic, hypoinsulinaemic hypoglycaemia and no AKT2 mutation underwent further genetic, clinical and metabolic investigation. Signalling in dermal fibroblasts from one patient and efficacy of the mTOR inhibitor Sirolimus on pathway activation were examined. Finally, the metabolic profile of a cohort of 19 further patients with mosaic activating mutations in PI3K was assessed.

RESULTS

In the first three patients, mosaic mutations in PIK3CA (p.Gly118Asp or p.Glu726Lys) or PIK3R2 (p.Gly373Arg) were found. In different tissue samples available from one patient, the PIK3CA p.Glu726Lys mutation was present at burdens from 24% to 42%, with the highest level in the liver. Dermal fibroblasts showed increased basal AKT phosphorylation which was potently suppressed by Sirolimus. Nineteen further patients with mosaic mutations in PIK3CA had neither clinical nor biochemical evidence of hypoglycaemia.

CONCLUSIONS

Mosaic mutations activating class 1A PI3K cause severe non-ketotic hypoglycaemia in a subset of patients, with the metabolic phenotype presumably related to the extent of mosaicism within the liver. mTOR or PI3K inhibitors offer the prospect for future therapy.

Cataract and optic disk drusen in a patient with glycogenosis and di George syndrome: clinical and molecular report

Background

We report the ophthalmic findings of a patient with type Ia glycogen storage disease (GSD Ia), DiGeorge syndrome (DGS), cataract and optic nerve head drusen (ONHD).

Case presentation

A 26-year-old white woman, born at term by natural delivery presented with a post-natal diagnosis of GSD Ia. Genetic testing by array-comparative genomic hybridization (CGH) for DGS was required because of her low levels of serum calcium. The patient has been followed from birth, attending the day-hospital every six months at the San Paolo Hospital, Milan, outpatient clinic for metabolic diseases and previously at another eye center. During the last day-hospital visit, a complete eye examination showed ONHD and cataract in both eyes. Next Generation Sequencing (NGS) was subsequently done to check for any association between the eye problems and metabolic aspects.

Conclusions

This is the first description of ocular changes in a patient with GSD Ia and DGS. Mutations explaining GSD Ia and DGS were found but no specific causative mutation for cataract and ONHD. The metabolic etiology of her lens changes is known, whereas the pathogenesis of ONHD is not clear. Although the presence of cataract and ONHD could be a coincidence; the case reported could suggest that hypocalcemia due to DGS could be the common biochemical pathway.

Glycogen storage disease type IX and growth hormone deficiency presenting as severe ketotic hypoglycemia

BACKGROUND

Glycogen storage disease (GSD) type IX and growth hormone (GH) deficiency cause ketotic hypoglycemia via different mechanisms and are not known to be associated. We describe a patient presenting with severe ketotic hypoglycemia found to have both GSD IX and isolated GH deficiency.

CASE PRESENTATION

A 3-year-and-11-month-old boy with a history of prematurity, autism, developmental delay, seizures, and feeding difficulty was admitted for poor weight gain and symptomatic hypoglycemia. He was nondysmorphic, with a height of 93.8 cm (2%, -1.97 SDS), and has no hepatomegaly. He developed symptomatic hypoglycemia, with a serum glucose level of 37 mg/dL after 14 h of fasting challenge. Critical sample showed a GH of 0.24 ng/mL. GH provocative stimulation testing was done with a peak GH of 2.8 ng/mL. Brain magnetic resonance imaging showed a hypoplastic pituitary gland. Given the clinical symptoms, suspicion for mitochondrial disease was high. Dual Genome Panel by Massively Parallel Sequencing revealed a hemizygous variant c.721A>G (p1241V) in the X-linked PHKA2 gene, a causative gene for GSD IX. Red blood cell PhK enzyme activity testing was low, supporting the diagnosis.

CONCLUSIONS

Given the patient's developmental delays that were not explained by GH deficiency alone, further investigation showed two unrelated conditions resulting in deranged metabolic adaptation to fasting leading to severe hypoglycemia.

The structure of brain glycogen phosphorylase-from allosteric regulation mechanisms to clinical perspectives

Glycogen phosphorylase (GP) is the key enzyme that regulates glycogen mobilization in cells. GP is a complex allosteric enzyme that comprises a family of three isozymes: muscle GP (mGP), liver GP (lGP), and brain GP (bGP). Although the three isozymes display high similarity and catalyze the same reaction, they differ in their sensitivity to the allosteric activator adenosine monophosphate (AMP). Moreover, inactivating mutations in mGP and lGP have been known to be associated with glycogen storage diseases (McArdle and Hers disease, respectively). The determination, decades ago, of the structure of mGP and lGP have allowed to better understand the allosteric regulation of these two isoforms and the development of specific inhibitors. Despite its important role in brain glycogen metabolism, the structure of the brain GP had remained elusive. Here, we provide an overview of the human brain GP structure and its relationship with the two other members of this key family of the metabolic enzymes. We also summarize how this structure provides valuable information to understand the regulation of bGP and to design specific ligands of potential pharmacological interest.

Var2GO: a web-based tool for gene variants selection

Background

One of the most challenging issue in the variant calling process is handling the resulting data, and filtering the genes retaining only the ones strictly related to the topic of interest. Several tools permit to gather annotations at different levels of complexity for the detected genes and to group them according to the pathways and/or processes they belong to. However, it might be a time consuming and frustrating task. This is partly due to the size of the file, that might contain many thousands of genes, and to the search of associated variants that requires a gene-by-gene investigation and annotation approach. As a consequence, the initial gene list is often reduced exploiting the knowledge of variants effect, novelty and genotype, with the potential risk of losing meaningful pieces of information.

Results

Here we present Var2GO, a new web-based tool to support the annotation and filtering of variants and genes coming from variant calling of high-throughput sequencing data. Var2GO permits to upload either the unprocessed Variant Calling Format file or a table containing the annotated variants. The raw data undergo a preliminary step of variants annotation, using the SnpEff tool, and are converted to a table format. The table is then uploaded into an on the fly generated database. Genes associated to the variants are automatically annotated with the corresponding Gene Ontology terms covering the three GO domains. Using the web interface it is then possible to filter and extract, from the whole list, genes having annotations in the domain of interest, by simply specifying filtering parameters and one or more keywords. The relevance of this tool is demonstrated on exome sequencing data.

Conclusions

Var2GO is a novel tool that implements a topic-based approach, expressly designed to help biologists in narrowing the search of relevant genes coming from variant calling analysis. Its main purpose is to support non-bioinformaticians in handling and processing raw variant calling data through an intuitive web interface. Furthermore, Var2GO offers a complete pipeline that, starting from the raw VCF file, allows to annotate both variants and associated genes and supports the extraction of relevant biological knowledge.

Serum and Muscle Metabolomics for the Prediction of Ultimate pH, a Key Factor for Chicken-Meat Quality

Variations in muscle glycogen storage are highly correlated with variations in meat ultimate pH (pHu), a key factor for poultry meat quality. A total of two chicken lines were divergently selected on breast pHu to understand the biological basis for variations in meat quality (i.e., the pHu- and the pHu+ lines that are characterized by a 17% difference in muscle glycogen content). The effects of this selection on bird metabolism were investigated by quantifying muscle metabolites by high-resolution NMR ((1)H and (31)P) and serum metabolites by (1)H NMR. A total of 20 and 26 discriminating metabolites between the two lines were identified by orthogonal partial least-squares discriminant analysis (OPLS-DA) in the serum and muscle, respectively. There was over-representation of carbohydrate metabolites in the serum and muscle of the pHu- line, consistent with its high level of muscle glycogen. However, the pHu+ line was characterized by markers of oxidative stress and muscle catabolism, probably because of its low level of energy substrates. After OPLS-DA multiblock analysis, a metabolic set of 15 high-confidence biomarkers was identified that could be used to predict the quality of poultry meat after validation on an independent population.

Lens opacities in glycogenoses type I and III

OBJECTIVE

The glycogen storage diseases (GSD) or glycogenoses comprise several inherited diseases caused by abnormalities of the enzymes that regulate the synthesis or degradation of glycogen. This report presents lens opacities not previously described in patients with type I or III GSD.

PARTICIPANTS

Eleven patients with type I and III GSD.

METHODS

We examined a series of 11 consecutive patients (aged 13-40 years) with type I and III GSD by full ophthalmologic examination.

RESULTS

We found changes of the lens on 7 of 11 patients (aged 23-40 years) with glycogenoses I and III. In 6 patients, the lens showed multiple, bilateral, punctate, and peripheral opacities; only 1 patient showed a posterior subcapsular opacity in both eyes. We did not observe changes in the cornea and the posterior pole correlated to the accumulation of glycogen and lipids.

CONCLUSIONS

In this series, we found that 60% of patients with type I and III GSD show lens opacities. These opacities are bilateral, peripheral, multiple, and small; they do not give any visual disturbance. Considering that subjects with age ranging from 13 to 23 years had no lens opacities, we postulate that they could progressively develop over time because of exposure to recurrent attacks of hypoglycemia, which lead to a progressive depletion of hexokinase.

Suppressed glycolytic metabolism in the prostate of transgenic rats overexpressing calcium-binding protein regucalcin underpins reduced cell proliferation

Regucalcin (RGN) is a calcium-binding protein underexpressed in human prostate cancer cases, and it has been associated with the suppression of cell proliferation and the regulation of several metabolic pathways. On the other hand, it is known that the metabolic reprogramming with augmented glycolytic metabolism and enhanced proliferative capability is a characteristic of prostate cancer cells. The present study investigated the influence of RGN on the glycolytic metabolism of rat prostate by comparing transgenic adult animals overexpressing RGN (Tg-RGN) with their wild-type counterparts. Glucose consumption was significantly decreased in the prostate of Tg-RGN animals relatively to wild-type, and accompanied by the diminished expression of glucose transporter 3 and glycolytic enzyme phosphofructokinase. Also, prostates of Tg-RGN animals displayed lower lactate levels, which resulted from the diminished expression/activity of lactate dehydrogenase. The expression of the monocarboxylate transporter 4 responsible for the export of lactate to the extracellular space was also diminished with RGN overexpression. These results showed the effect of RGN in inhibiting the glycolytic metabolism in rat prostate, which was underpinned by a reduced cell proliferation index. The present findings also suggest that the loss of RGN may predispose to a hyper glycolytic profile and fostered proliferation of prostate cells.

Safety and Efficacy of Chronic Extended Release Cornstarch Therapy for Glycogen Storage Disease Type I

BACKGROUND

Glycogen storage disease type I (GSD I) causes severe hypoglycemia during periods of fasting since both glycogenolysis and gluconeogenesis are impaired. Primary treatment in North America consists of cornstarch therapy every 3-4 h. Waxy maize extended release cornstarch was introduced for maintaining overnight glucose concentrations, but no studies have assessed long-term safety and efficacy of the product.

OBJECTIVE

To demonstrate the safety and efficacy of modified cornstarch in GSD I.

DESIGN

An open-label overnight trial of extended release cornstarch was performed. Subjects with a successful trial (optimal metabolic control 2 or more hours longer than with traditional cornstarch) were given the option of continuing into the chronic observational phase. Subjects were assessed biochemically at baseline and after 12 months.

RESULTS

Of the 106 subjects (93 GSD Ia/13 GSD Ib), efficacy was demonstrated in 82 patients (88%) with GSD Ia and 10 patients (77%) with GSD Ib. The success rate for extending fasting was 95% for females and 78% for males. Of the patients who entered the longitudinal phase, long-term data are available for 44 subjects. Mean duration of fasting on traditional cornstarch prior to study for the cohort was 4.1 and 7.8 h on the extended release cornstarch (P < 0.001). All laboratory markers of metabolic control have remained stable in the chronically treated patients.

CONCLUSION

Extended release cornstarch appears to improve the quality of life of patients with GSD I without sacrificing metabolic control. Avoiding the overnight dose of cornstarch should enhance safety in this population.

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.