Prevention of complications in glycogen storage disease type Ia with optimization of metabolic control

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.

Short and long-term acceptability and efficacy of extended-release cornstarch in the hepatic glycogen storage diseases: results from the Glyde study

BACKGROUND

Hypoglycaemia is the primary manifestation of all the hepatic types of glycogen storage disease (GSD). In 2008, Glycosade®, an extended-release waxy maize cornstarch, was reported as an alternative to uncooked cornstarch (UCCS) which could prolong the duration of fasting in the GSD population. To date, there has been minimal published experience in (a) young children, (b) the ketotic forms of GSD, and (c) with daytime dosing. The Glyde study was created as a prospective, global initiative to test the efficacy and tolerance of Glycosade use across a broader and more diverse population.

METHODS

A randomised double-blind cross-over fasting study assessing the tolerance and efficacy of Glycosade compared with cornstarch was performed across disease types and ages. Participants and clinicians chose the product deemed superior, whilst still blinded. Participants were followed for 2 years to assess long-term metabolic control, growth, and quality of life.

RESULTS

Sixty-one participants (age 2-62 years; 59% female) were enrolled, and 58 participants completed the fasting studies (28 GSD I; 30 GSD III, VI, IX). Glycosade improved duration of fasting in GSD I and duration of fasting without ketosis in the ketotic forms. Chronic Glycosade use was chosen by 69% of participants. Those treated with Glycosade for the 2-year chronic phase used fewer doses of therapy while markers of metabolic control remained stable.

CONCLUSION

The Glyde study is the first multi-centre international trial demonstrating the efficacy and tolerance of Glycosade in a large cohort of hepatic GSD patients across a diverse international population. The ability to use fewer doses of therapy per day and avoidance of overnight therapy may improve compliance, safety, and quality of life without sacrificing metabolic control.

Medium-Chain Triglyceride Oil and Dietary Intervention Improved Body Composition and Metabolic Parameters in Children with Glycogen Storage Disease Type 1 in Jordan: A Clinical Trial

Glycogen storage diseases (GSDs) are a group of carbohydrate metabolism disorders, most of which are inherited in autosomal recessive patterns. GSDs are of two types: those that have to do with liver and hypoglycaemia (hepatic GSDs) and those that are linked to neuromuscular presentation. This study aims to assess the impact of dietary intervention, including medium-chain triglyceride (MCT) oil, on anthropometric measurements, body composition analysis and metabolic parameters among Jordanian children and is expected to be the first in the country. A sample of 38 children with glycogen storage disease type 1 (GSD-1) (median age = 6.4 years) were on a diet that included uncooked cornstarch therapy and a fructose-, sucrose- and lactose-restricted diet. Patients started to take MCT oil along with the prescribed diet after the first body composition test. Patients' nutritional status was re-evaluated three months later. The study results show that the percentage of patients who suffered from hypoglycaemia at the beginning of the study decreased significantly from 94.7% to 7.9% (p < 0.0001). The serum levels of triglycerides, cholesterol, uric acid and lactate decreased significantly after three months of intervention (100-71.1%, 73.7-21.1%, 97.4-52.6% and 94.7-18.4%, respectively). In contrast, there was no statistical difference in neutrophil count. Regarding clinical parameters, liver span was significantly reduced from (16.01 ± 2.65 cm) to (14.85 ± 2.26 cm) (p < 0.0001). There were significant improvements in growth parameters, including height-for-age and BMI-for-age for children aged ≥2 years (p = 0.034 and p = 0.074, respectively). Significant improvements in skeletal muscle mass and bone mineral content were also noticed at the end of the trial (p ≤ 0.05). In conclusion, medium-chain triglyceride therapy is found to improve biochemical and growth parameters in children with GSD-1 in Jordan.

Gene therapy for glycogen storage diseases

Glycogen storage disorders (GSDs) are inherited disorders of metabolism resulting from the deficiency of individual enzymes involved in the synthesis, transport, and degradation of glycogen. This literature review summarizes the development of gene therapy for the GSDs. The abnormal accumulation of glycogen and deficiency of glucose production in GSDs lead to unique symptoms based upon the enzyme step and tissues involved, such as liver and kidney involvement associated with severe hypoglycemia during fasting and the risk of long-term complications including hepatic adenoma/carcinoma and end stage kidney disease in GSD Ia from glucose-6-phosphatase deficiency, and cardiac/skeletal/smooth muscle involvement associated with myopathy +/- cardiomyopathy and the risk for cardiorespiratory failure in Pompe disease. These symptoms are present to a variable degree in animal models for the GSDs, which have been utilized to evaluate new therapies including gene therapy and genome editing. Gene therapy for Pompe disease and GSD Ia has progressed to Phase I and Phase III clinical trials, respectively, and are evaluating the safety and bioactivity of adeno-associated virus vectors. Clinical research to understand the natural history and progression of the GSDs provides invaluable outcome measures that serve as endpoints to evaluate benefits in clinical trials. While promising, gene therapy and genome editing face challenges with regard to clinical implementation, including immune responses and toxicities that have been revealed during clinical trials of gene therapy that are underway. Gene therapy for the glycogen storage diseases is under development, addressing an unmet need for specific, stable therapy for these conditions.

Development of hepatocellular adenomas in a patient with glycogen storage disease Ia treated with growth hormone therapy

Glycogen storage disease Ia (GSD Ia), also known as von Gierke disease, is caused by pathogenic variants in the G6PC1 gene (OMIM 232200) which encodes glucose-6-phosphatase. Deficiency of glucose-6-phosphatase impairs the processes of gluconeogenesis and glycogenolysis by preventing conversion of glucose-6-phosphate to glucose. Clinical features include fasting hypoglycemia, lactic acidosis, hypertriglyceridemia, hyperuricemia, hepatomegaly, and development of hepatocellular adenomas (HCAs) with potential for malignant transformation. Additionally, patients with GSD Ia often exhibit short stature, in some instances due to growth hormone (GH) deficiency. Patients with short stature caused by GH deficiency typically receive GH injections. Here, we review the literature and describe a female with GSD Ia who had short stature, failure of growth progression, and suspected GH deficiency. This patient received GH injections from ages 11 to 14 years under careful monitoring of an endocrinologist and developed HCAs during that time. To date, there is no reported long-term follow up data on patients with GSD Ia who have received GH therapy, and therefore the clinical outcomes post-GH therapy are unclear.

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.

Gene therapy and genome editing for type I glycogen storage diseases

Type I glycogen storage diseases (GSD-I) consist of two major autosomal recessive disorders, GSD-Ia, caused by a reduction of glucose-6-phosphatase-α (G6Pase-α or G6PC) activity and GSD-Ib, caused by a reduction in the glucose-6-phosphate transporter (G6PT or SLC37A4) activity. The G6Pase-α and G6PT are functionally co-dependent. Together, the G6Pase-α/G6PT complex catalyzes the translocation of G6P from the cytoplasm into the endoplasmic reticulum lumen and its subsequent hydrolysis to glucose that is released into the blood to maintain euglycemia. Consequently, all GSD-I patients share a metabolic phenotype that includes a loss of glucose homeostasis and long-term risks of hepatocellular adenoma/carcinoma and renal disease. A rigorous dietary therapy has enabled GSD-I patients to maintain a normalized metabolic phenotype, but adherence is challenging. Moreover, dietary therapies do not address the underlying pathological processes, and long-term complications still occur in metabolically compensated patients. Animal models of GSD-Ia and GSD-Ib have delineated the disease biology and pathophysiology, and guided development of effective gene therapy strategies for both disorders. Preclinical studies of GSD-I have established that recombinant adeno-associated virus vector-mediated gene therapy for GSD-Ia and GSD-Ib are safe, and efficacious. A phase III clinical trial of rAAV-mediated gene augmentation therapy for GSD-Ia (NCT05139316) is in progress as of 2023. A phase I clinical trial of mRNA augmentation for GSD-Ia was initiated in 2022 (NCT05095727). Alternative genetic technologies for GSD-I therapies, such as gene editing, are also being examined for their potential to improve further long-term outcomes.

Cytokine profiling in patients with hepatic glycogen storage disease: Are there clues for unsolved aspects?

INTRODUCTION

Hepatic Glycogen Storage Diseases (GSD) are rare genetic disorders in which the gluconeogenesis pathway is impaired. Cytokines control virtually every aspect of physiology and may help to elucidate some unsolved questions about phenotypes presented by GSD patients.

METHODS

This was an exploratory study in which 27 GSD patients on treatment (Ia = 16, Ib = 06, III = 02, IXα = 03) and 24 healthy age- and sex-matched subjects had plasma samples tested for a panel of 20 cytokines (G-CSF,GM-CSF, IL-1α,IL-1β, IL-4, IL-6, IL-8, IL-10, IL-13, IL-17A, GRO, IP-10/CXCL10, MCP-1/CCL2, MIP-1α/CCL3, MIP-1β/CCL4, MDC/CCL22, IFN-γ, TNF-α, TNF-β, VEGF) through a multiplex kit and analyzed in comparison to controls and among patients, regarding to clinical features as anemia, hepatic adenocarcinoma and triglyceride levels.

RESULTS

Patients (GSD-Ia/III/IX) presented reduced levels of IL-4 (p = 0.040), MIP-1α/CCL3 (p = 0.003), MDC/CCL22 (p < 0.001), TNF-β (p = 0.045) and VEGF (p = 0.043) compared to controls. When different types of GSD were compared, G-CSF was higher in GSD-Ib than -Ia (p < 0.001) and than -III/IX (p = 0.033) patients; IL-10 was higher in GSD-Ib than in GSD-Ia patients (p = 0.019); and GSD-III/IX patients had increased levels of IP-10/CXCL10 than GSD-Ib patients (p = 0.019). When GSD-I patients were gathered into the same group and compared with GSD-III/IX patients, IP10/CXCL10 and MCP-1 were higher in the latter group (p = 0.005 and p = 0.013, respectively). GSD-I patients with anemia presented higher levels of IL-4 and MIP-1α in comparison with patients who had not. Triglyceride level was correlated with neutrophil count and MDC levels on GSD-Ia patients without HCA.

CONCLUSION

Altogether, altered levels of cytokines in GSD-I patients reflect an imbalance in immunoregulation process. This study also indicates that neutrophils and some cytokines are affected by triglyceride levels, and future studies on the theme should consider this variable.

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.

Glycogen storage disease type 1a in the Ohio Amish

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

A Prospective Study on Continuous Glucose Monitoring in Glycogen Storage Disease Type Ia: Toward Glycemic Targets

CONTEXT

Although previous research has shown the benefit of continuous glucose monitoring (CGM) for hepatic glycogen storage diseases (GSDs), current lack of prospectively collected CGM metrics and glycemic targets for CGM-derived outcomes in the hepatic GSD population limits its use.

OBJECTIVE

To assess CGM metrics for glycemic variation and glycemic control in adult patients with GSDIa as compared to matched healthy volunteers.

DESIGN

Prospective CGM data were collected during the ENGLUPRO GSDIa trial (NCT04311307) in which a Dexcom G6 device was used. Ten adult patients with GSDIa and 10 age-, sex- and body mass index-matched healthy volunteers were enrolled. Capillary blood glucose was concurrently measured during 2 standardized 2-hour time intervals. Descriptive [eg, glycemic variability (GV), time below range, time in range (TIR), time above range (TAR)] and advanced (ie, first- and second-order derivatives, Fourier analysis) CGM outcomes were calculated. For each descriptive CGM outcome measure, 95% CIs were computed in patients with GSDIa and healthy volunteers, respectively.

RESULTS

CGM overestimation was higher under preprandial and level 1 hypoglycemia (ie, capillary glucose values ≥ 3.0 mmol/L and < 3.9 mmol/L) conditions. GV and TAR were higher while TIR was lower in patients with GSDIa compared to healthy volunteers (P < 0.05). Three patients with GSDIa showed descriptive CGM outcomes outside the calculated 95% CI in GSDIa patients. Advanced CGM analysis revealed a distinct pattern (ie, first- and second-order derivatives and glucose curve amplitude) in each of these 3 patients within the patients group.

CONCLUSIONS

This is the first study to prospectively compare CGM outcomes between adult patients with GSDIa and matched healthy volunteers. The generation of a set of CGM metrics will provide guidance in using and interpreting CGM data in GSDIa and will be useful for the definition of glycemic targets for CGM in patients with GSDIa. Future studies should investigate the prognostic value of CGM outcomes and their major determinants in patients with GSDIa.

Prevalence and Complications of Glycogen Storage Disease in South Korea: A Nationwide Population-Based Study, 2007-2018

Glycogen storage disease (GSD) is a rare disease that can cause life-threatening problems owing to metabolic errors in storing or using glycogen. The disease course of GSD remains unknown, despite medical technology advances. We determined the prevalence and complications of GSD using data from the National Health Insurance Service database. Data were collected and analyzed for the entire South Korean population with GSD during 2007–2018. GSD was defined as a combination of disease code E74.0 and rare incurable disease insurance code V117, a unique disease code combination for GSD in South Korea. Overall, 23,055 patients had the E74 disease code; 404 had an additional V117 insurance code. Most GSD patients were aged <10 years. Many complications were identified, the most common being hepatomegaly, hyperuricemia, and elevated liver enzyme levels. The most prescribed drug was α-glucosidase, followed by allopurinol. Seventy-two percent of patients were treated in pediatrics. Twenty-five patients underwent liver transplantation, and 14 died after GSD diagnosis. In South Korea, more patients than expected had GSD diagnosis and were managed accordingly. GSD causes many complications and hospitalizations, resulting in high medical expenses. Serious complications can result in liver transplantation and, eventually, death in some cases. Although the patients' condition was identified only by the disease code, this is the first study to present the current situation of GSD patients in South Korea. Because GSD patients can have dangerous medical conditions, they should be managed consistently while minimizing various complications that may occur with optimal metabolic control.

High childhood serum triglyceride concentrations associate with hepatocellular adenoma development in patients with glycogen storage disease type Ia

Background & Aims

Glycogen storage disease type Ia (GSDIa) is an inborn error of carbohydrate metabolism caused by pathogenic variants in the glucose-6-phosphatase catalytic subunit 1 (G6PC1) gene and is associated with hepatocellular adenoma (HCA) formation. Data on risk factors for HCA occurrence in GSDIa are scarce. We investigated HCA development in relation to sex, G6PC1 genotype, and serum triglyceride concentration (TG).

Methods

An observational study of patients with genetically confirmed GSDIa ≥12 years was performed. Patients were categorised for sex; presence of 2, 1, or 0 predicted severe G6PC1 variant (PSV); and median TG during childhood (<12 years; stratified for above/below 5.65 mmol/L, i.e. 500 mg/dl).

Results

Fifty-three patients (23 females) were included, of which 26 patients developed HCA at a median (IQR) age of 21 (17–25) years. At the age of 25 years, 48% of females and 30% of males had developed HCA (log-rank p = 0.045). Two-thirds of patients with GSDIa carried 2 PSVs, 20% carried 1, and 13% carried none. Neither the number of PSVs nor any specific G6PC1 variants were associated with HCA occurrence. Childhood TG was 3.4 (3.0–4.2) mmol/L in males vs. 5.6 (4.0–7.9) mmol/L in females (p = 0.026). Childhood TG >5.65 mmol/L was associated with HCA development at younger age, compared with patients with childhood TG <5.65 mmol/L (18 vs. 33 years; log-rank p = 0.001). Cox regression analysis including TG, sex, and TG–sex interaction correction revealed childhood TG >5.65 mmol/L as an independent risk factor for HCA development (hazard ratio [HR] 6.0; 95% CI 1.2–29.8; p = 0.028).

Conclusions

In patients with GSDIa, high childhood TG was associated with an increased risk of HCA, and earlier onset of HCA development, independent of sex-associated hypertriglyceridaemia, and G6PC1 genotype.

Lay summary

Glycogen storage disease type Ia (GSDIa) is a rare, inherited metabolic disease that can be complicated by liver tumours (hepatocellular adenomas), which in turn may cause bleeding or progress to liver cancer. Risk factors associated with hepatocellular adenoma formation in patients with GSDIa are largely unknown. In our study, we found that high serum triglyceride concentrations during childhood, but not specific genetic variants, were associated with increased risk of hepatocellular adenoma diagnosis later in life.

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Glycogen storage disease Ia (GSDIa) is a metabolic disease caused by mutations in glucose-6-phosphatase catalytic subunit 1 (G6PC1).

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Patients with GSDIa often develop hepatocellular adenoma (HCA), with unclear risk factors.

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Metabolic control in GSDIa is commonly evaluated through serum triglyceride concentration (TG).

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Patients with GSDIa with high childhood TG had increased risk and earlier onset of HCA.

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Sex-associated hypertriglyceridaemia and G6PC1 genotype were not associated with HCA.

Case Report: Glycogen Storage Disease Type Ia in a Chinese Child Treated With Growth Hormone

BACKGROUND

Glycogen storage disease type Ia is a rare metabolic disorder that leads to excessive glycogen and fat accumulation in organs, characterized by hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, puberty delay, and growth retardation. Here, we report on a patient with glycogen storage disease type Ia treated with growth hormone.

CASE PRESENTATION

A 10-year-old boy had growth retardation for 6 years, and was admitted to clarify the cause of his short stature. We found that his bone age was 5.5 years, significantly lower than his physical age, while his serum IGF-1 and IGFBP-3 were 23.30 and 1620.0 ng/mL, respectively, both lower than normal. His medical history revealed that he had suffered from steatohepatitis, hyperlipidemia, and hypoglycemia since he was 11 months of age. Whole exome sequencing (WES) showed compound heterozygous mutations in exons 2 and 5 of the glucose-6-phosphatase (G6PC) gene on chromosome 17: c.G248A (p.R83H) and c.G648T (p.L216L). The patient was finally diagnosed with GSD Ia. After growth hormone (GH) treatment and corn starch therapy for 14 months, his height significantly increased (by 13 cm). The serum IGF-1 level increased to the normal range but his lipid levels and liver function did not significantly increase.

CONCLUSION

We describe a young patient with a compound heterozygous G6PC variant in a Chinese family; his height increased significantly after growth hormone and corn starch interventions. This case emphasizes that WES is essential for early diagnosis, and that growth hormone treatment may increase the height of patients with GSD Ia safely.

Exosomal MicroRNAs as Potential Biomarkers of Hepatic Injury and Kidney Disease in Glycogen Storage Disease Type Ia Patients

Glycogen storage disease type Ia (GSDIa) is an inherited metabolic disorder caused by mutations in the enzyme glucose-6-phosphatase-α (G6Pase-α). Affected individuals develop renal and liver complications, including the development of hepatocellular adenoma/carcinoma and kidney failure. The purpose of this study was to identify potential biomarkers of the evolution of the disease in GSDIa patients. To this end, we analyzed the expression of exosomal microRNAs (Exo-miRs) in the plasma exosomes of 45 patients aged 6 to 63 years. Plasma from age-matched normal individuals were used as controls. We found that the altered expression of several Exo-miRs correlates with the pathologic state of the patients and might help to monitor the progression of the disease and the development of late GSDIa-associated complications.

Hepatocyte-specific glucose-6-phosphatase deficiency disturbs platelet aggregation and decreases blood monocytes upon fasting-induced hypoglycemia

OBJECTIVE

Glycogen storage disease type 1a (GSD Ia) is a rare inherited metabolic disorder caused by mutations in the glucose-6-phosphatase (G6PC1) gene. When untreated, GSD Ia leads to severe fasting-induced hypoglycemia. Although current intensive dietary management aims to prevent hypoglycemia, patients still experience hypoglycemic events. Poor glycemic control in GSD Ia is associated with hypertriglyceridemia, hepatocellular adenoma and carcinoma, and also with an increased bleeding tendency of unknown origin.

METHODS

To evaluate the effect of glycemic control on leukocyte levels and coagulation in GSD Ia, we employed hepatocyte-specific G6pc1 deficient (L-G6pc-/-) mice under fed or fasted conditions, to match good or poor glycemic control in GSD Ia, respectively.

RESULTS

We found that fasting-induced hypoglycemia in L-G6pc-/- mice decreased blood leukocytes, specifically proinflammatory Ly6Chi monocytes, compared to controls. Refeeding reversed this decrease. The decrease in Ly6Chi monocytes was accompanied by an increase in plasma corticosterone levels and was prevented by the glucocorticoid receptor antagonist mifepristone. Further, fasting-induced hypoglycemia in L-G6pc-/- mice prolonged bleeding time in the tail vein bleeding assay, with reversal by refeeding. This could not be explained by changes in coagulation factors V, VII, or VIII, or von Willebrand factor. While the prothrombin and activated partial thromboplastin time as well as total platelet counts were not affected by fasting-induced hypoglycemia in L-G6pc-/- mice, ADP-induced platelet aggregation was disturbed.

CONCLUSIONS

These studies reveal a relationship between fasting-induced hypoglycemia, decreased blood monocytes, and disturbed platelet aggregation in L-G6pc-/- mice. While disturbed platelet aggregation likely accounts for the bleeding phenotype in GSD Ia, elevated plasma corticosterone decreases the levels of proinflammatory monocytes. These studies highlight the necessity of maintaining good glycemic control in GSD Ia.

Modeling Phenotypic Heterogeneity of Glycogen Storage Disease Type 1a Liver Disease in Mice by Somatic CRISPR/CRISPR-associated protein 9-Mediated Gene Editing

BACKGROUND AND AIMS

Patients with glycogen storage disease type 1a (GSD-1a) primarily present with life-threatening hypoglycemia and display severe liver disease characterized by hepatomegaly. Despite strict dietary management, long-term complications still occur, such as liver tumor development. Variations in residual glucose-6-phosphatase (G6PC1) activity likely contribute to phenotypic heterogeneity in biochemical symptoms and complications between patients. However, lack of insight into the relationship between G6PC1 activity and symptoms/complications and poor understanding of the underlying disease mechanisms pose major challenges to provide optimal health care and quality of life for GSD-1a patients. Currently available GSD-1a animal models are not suitable to systematically investigate the relationship between hepatic G6PC activity and phenotypic heterogeneity or the contribution of gene-gene interactions (GGIs) in the liver.

APPROACH AND RESULTS

To meet these needs, we generated and characterized a hepatocyte-specific GSD-1a mouse model using somatic CRISPR/CRISPR-associated protein 9 (Cas9)-mediated gene editing. Hepatic G6pc editing reduced hepatic G6PC activity up to 98% and resulted in failure to thrive, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly, hepatic steatosis (HS), and increased liver tumor incidence. This approach was furthermore successful in simultaneously modulating hepatic G6PC and carbohydrate response element-binding protein, a transcription factor that is activated in GSD-1a and protects against HS under these conditions. Importantly, it also allowed for the modeling of a spectrum of GSD-1a phenotypes in terms of hepatic G6PC activity, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly and HS.

CONCLUSIONS

In conclusion, we show that somatic CRISPR/Cas9-mediated gene editing allows for the modeling of a spectrum of hepatocyte-borne GSD-1a disease symptoms in mice and to efficiently study GGIs in the liver. This approach opens perspectives for translational research and will likely contribute to personalized treatments for GSD-1a and other genetic liver diseases.

Modifiable factors affecting renal preservation in type I glycogen storage disease after liver transplantation: a single-center propensity-match cohort study

BACKGROUND AND AIMS

Glycogen storage disease type I (GSD-I) is an autosomal recessive disorder of carbohydrate metabolism, resulting in limited production of glucose and excessive glycogen storage in the liver and kidneys. These patients are characterized by life-threatening hypoglycemia, metabolic derangements, hepatomegaly, chronic kidney disease, and failure to thrive. Liver transplantation (LT) has been performed for poor metabolic control and delayed growth. However, renal outcome was diverse in pediatric GSD patients after LT. The aim of this study was to investigate the long-term outcome of renal function in pediatric GSD-I patients after living donor LT (LDLT), and to identify modifiable variables that potentially permits LT to confer native renal preservation.

METHODS

The study included eight GSD-Ia and one GSD-Ib children with a median age of 9.0 (range 4.2-15.7) years at the time of LT. Using propensity score matching, 20 children with biliary atresia (BA) receiving LT were selected as the control group by matching for age, sex, pre-operative serum creatinine (SCr) and pediatric end-stage liver disease (PELD) score. Renal function was evaluated based on the SCr, estimated glomerular filtration rate (eGFR), microalbuminuria, and morphological changes in the kidneys. Comparability in long-term renal outcome in terms of anatomic and functional parameters will help to identify pre-LT factors of GSD-I that affect renal prognosis.

RESULTS

The clinical and biochemical characteristics of the GSD and BA groups were similar, including immunosuppressive regimens and duration of follow-up (median 15 years) after LT. Overall, renal function, including eGFR and microalbuminuria was comparable in the GSD-I and BA groups (median eGFR: 111 vs. 123 ml/min/1.73m2, P = 0.268; median urine microalbuminuria to creatinine ratio: 16.0 vs. 7.2 mg/g, P = 0.099, respectively) after LT. However, in the subgroups of the GSD cohort, patients starting cornstarch therapy at an older age (≥ 6-year-old) before transplantation demonstrated a worse renal outcome in terms of eGFR change over years (P < 0.001). In addition, the enlarged kidney in GSD-I returned to within normal range after LT.

CONCLUSIONS

Post-LT renal function was well-preserved in most GSD-I patients. Early initiation of cornstarch therapy before preschool age, followed by LT, achieved a good renal prognosis.

A retrospective in-depth analysis of continuous glucose monitoring datasets for patients with hepatic glycogen storage disease: Recommended outcome parameters for glucose management

Continuous glucose monitoring (CGM) systems have great potential for real-time assessment of glycemic variation in patients with hepatic glycogen storage disease (GSD). However, detailed descriptions and in-depth analysis of CGM data from hepatic GSD patients during interventions are scarce. This is a retrospective in-depth analysis of CGM parameters, acquired in a continuous, real-time fashion describing glucose management in 15 individual GSD patients. CGM subsets are obtained both in-hospital and at home, upon nocturnal dietary intervention (n = 1), starch loads (n = 11) and treatment of GSD Ib patients with empagliflozin (n = 3). Descriptive CGM parameters, and parameters reflecting glycemic variation and glycemic control are considered useful CGM outcome parameters. Furthermore, the combination of first and second order derivatives, cumulative sum and Fourier analysis identified both subtle and sudden changes in glucose management; hence, aiding assessment of dietary and medical interventions. CGM data interpolation for nocturnal intervals reduced confounding by physical activity and diet. Based on these analyses, we conclude that in-depth CGM analysis can be a powerful tool to assess glucose management and optimize treatment in individual hepatic GSD patients.

Impaired Very-Low-Density Lipoprotein catabolism links hypoglycemia to hypertriglyceridemia in Glycogen Storage Disease type Ia

Prevention of hypertriglyceridemia is one of the biomedical targets in Glycogen Storage Disease type Ia (GSD Ia) patients, yet it is unclear how hypoglycemia links to plasma triglyceride (TG) levels. We analyzed whole-body TG metabolism in normoglycemic (fed) and hypoglycemic (fasted) hepatocyte-specific glucose-6-phosphatase deficient (L-G6pc^-/- ) mice. De novo fatty acid synthesis contributed substantially to hepatic TG accumulation in normoglycemic L-G6pc^-/- mice. In hypoglycemic conditions, enhanced adipose tissue lipolysis was the main driver of liver steatosis, supported by elevated free fatty acid concentrations in GSD Ia mice and GSD Ia patients. Plasma very-low-density lipoprotein (VLDL) levels were increased in GSD Ia patients and in normoglycemic L-G6pc^-/- mice, and further elevated in hypoglycemic L-G6pc^-/- mice. VLDL-TG secretion rates were doubled in normo- and hypoglycemic L-G6pc^-/- mice, while VLDL-TG catabolism was selectively inhibited in hypoglycemic L-G6pc^-/- mice. In conclusion, fasting-induced hypoglycemia in L-G6pc^-/- mice promotes adipose tissue lipolysis and arrests VLDL catabolism. This mechanism likely contributes to aggravated liver steatosis and dyslipidemia in GSD Ia patients with poor glycemic control and may explain clinical heterogeneity in hypertriglyceridemia between GSD Ia patients.

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.

Emerging roles of autophagy in hepatic tumorigenesis and therapeutic strategies in glycogen storage disease type Ia: A review

Glycogen storage disease type Ia (GSD-Ia) is an inherited metabolic disease caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC) which plays a critical role in blood glucose homeostasis by catalyzing the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate in the terminal step of glycogenolysis and gluconeogenesis. Patients with GSD-Ia manifest life-threatening fasting hypoglycemia along with the excessive accumulation of hepatic glycogen and triglycerides which results in hepatomegaly and a risk of long-term complications such as hepatocellular adenoma and carcinoma (HCA/HCC). The etiology of HCA/HCC development in GSD-Ia, however, is unknown. Recent studies have shown that the livers in model animals of GSD-Ia display impairment of autophagy, a cellular recycling process which is critical for energy metabolism and cellular homeostasis. However, molecular mechanisms of autophagy impairment and its involvement in pathogenesis in GSD-Ia are still under investigation. Here, we summarize the latest advances for signaling pathways implicated in hepatic autophagy impairment and the roles of autophagy in hepatic tumorigenesis in GSD-Ia. In addition, recent evidence has illustrated that autophagy plays an important role in hepatic metabolism and liver-directed gene therapy mediated by recombinant adeno-associated virus (rAAV). Therefore, we highlight the possible role of hepatic autophagy in metabolic control and rAAV-mediated gene therapy for GSD-Ia. In this review, we also provide potential therapeutic strategies for GSD-Ia on the basis of molecular mechanisms underlying hepatic autophagy impairment in GSD-Ia.

Dietary lipids in glycogen storage disease type III: A systematic literature study, case studies, and future recommendations

A potential role of dietary lipids in the management of hepatic glycogen storage diseases (GSDs) has been proposed, but no consensus on management guidelines exists. The aim of this study was to describe current experiences with dietary lipid manipulations in hepatic GSD patients. An international study was set up to identify published and unpublished cases describing hepatic GSD patients with a dietary lipid manipulation. A literature search was performed according to the Cochrane Collaboration methodology through PubMed and EMBASE (up to December 2018). All delegates who attended the dietetics session at the IGSD2017, Groningen were invited to share unpublished cases. Due to multiple biases, only data on GSDIII were presented. A total of 28 cases with GSDIII and a dietary lipid manipulation were identified. Main indications were cardiomyopathy and/or myopathy. A high fat diet was the most common dietary lipid manipulation. A decline in creatine kinase concentrations (n = 19, P < .001) and a decrease in cardiac hypertrophy in paediatric GSDIIIa patients (n = 7, P < .01) were observed after the introduction with a high fat diet. This study presents an international cohort of GSDIII patients with different dietary lipid manipulations. High fat diet may be beneficial in paediatric GSDIIIa patients with cardiac hypertrophy, but careful long-term monitoring for potential complications is warranted, such as growth restriction, liver inflammation, and hepatocellular carcinoma development.

Over 20-Year Follow-up of Patients with Hepatic Glycogen Storage Diseases: Single-Center Experience

BACKGROUND

The published data on the long-term outcomes of glycogen storage disease (GSD) patients is sparse in the literature. The aim of this study was to analyze the long-term (over 20 years) follow-up of patients with hepatic types of GSD-I, III, VI, and IX-from childhood to adulthood, managed by one referral center.

PATIENTS AND METHODS

Thirty adult patients with hepatic GSD were included in the study. A retrospective chart review of patients' medical records has been performed.

RESULTS

During the long-term follow-up, the most frequent complications observed in a group of 14 GSD I patients were nephropathy with blood hypertension (10/14), hyperuricemia (8/14), and development of hepatocellular adenomas (HCA; 5/14). All individuals but four presented with normal height. Two patients with GSD Ib suffered from inflammatory bowel disease (IBD). Nine (64%) GSD I patients were in balanced metabolic condition at the age of 18. Regarding GSD III/VI/IX, the most frequent complication was short stature observed in 5 out of 16 patients. All patients but one with GSD VI were in balanced metabolic condition at the age of 18.

CONCLUSION

The long-term outcomes of patients with GSD depend mainly on proper (adjusted to each type of GSD) dietary management and patient compliance. However, in GSD type I, even proper management does not eliminate all long-term complications in adulthood.

Dietary Management of the Glycogen Storage Diseases: Evolution of Treatment and Ongoing Controversies

The hepatic glycogen storage diseases (GSDs) are a group of disorders where abnormal storage or release of glycogen leads to potentially life-threatening hypoglycemia and metabolic disturbances. Dietary interventions have markedly improved the outcome for these disorders, from a previously fatal condition to one where people can do well with proper care. This article chronicles the evolution of dietary management and treatment of the hepatic GSDs (types 0, I, III, VI, IX, and XI). We examine historic and current approaches for preventing hypoglycemia associated with GSDs. There is a lack of consensus on the optimal dietary management of GSDs despite decades of research, and the ongoing controversies are discussed.

Fenofibrate rapidly decreases hepatic lipid and glycogen storage in neonatal mice with glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD Ia) is caused by autosomal mutations in glucose-6-phosphatase α catalytic subunit (G6PC) and can present with severe hypoglycemia, lactic acidosis and hypertriglyceridemia. In both children and adults with GSD Ia, there is over-accumulation of hepatic glycogen and triglycerides that can lead to steatohepatitis and a risk for hepatocellular adenoma or carcinoma. Here, we examined the effects of the commonly used peroxisomal proliferated activated receptor α agonist, fenofibrate, on liver and kidney autophagy and lipid metabolism in 5-day-old G6pc -/- mice serving as a model of neonatal GSD Ia. Five-day administration of fenofibrate decreased the elevated hepatic and renal triglyceride and hepatic glycogen levels found in control G6pc -/- mice. Fenofibrate also induced autophagy and promoted β-oxidation of fatty acids and stimulated gene expression of acyl-CoA dehydrogenases in the liver. These findings show that fenofibrate can rapidly decrease hepatic glycogen and triglyceride levels and renal triglyceride levels in neonatal G6pc -/- mice. Moreover, since fenofibrate is an FDA-approved drug that has an excellent safety profile, our findings suggest that fenofibrate could be a potential pharmacological therapy for GSD Ia in neonatal and pediatric patients as well as for adults. These findings may also apply to non-alcoholic fatty liver disease, which shares similar pathological and metabolic changes with GSD Ia.

Kidney and Metabolic Phenotypes in Glycogen Storage Disease Type-I Patients

Patients and Methods: A retrospective chart review of 32 GSD- I patients, followed at the American University of Beirut Medical Center, between 2007 and 2018 was conducted. Diagnosis was confirmed by enzymatic and/or genetic studies. Clinical presentation, growth, and kidney outcome were assessed. All patients were evaluated for body mass index, blood parameters of metabolic control including uric acid, alanine, lactic acid, and triglycerides in blood. Kidney evaluation included creatinine clearance, microalbuminuria, citraturia, and calciuria as well as urine microalbumin/creatinine ratio. Results: Almost one third of GSD-I patients developed microalbuminuria. This was detected below 7 months of age in 36% of patients who required early treatment with ACEI with significant reduction in albuminuria. Kidney stones were present in 6% and were associated with hypercalciuria and hypocitraturia. Poor metabolic control reflected by hyperuricemia, lactic acidosis, and hyperalaninemia were noted only in patients who developed microalbuminuria. Conclusion: Glomerular injury may appear in early infancy in poorly controlled patients. Adequate metabolic control and ACEI therapy may improve kidney outcome in GSD I patients. Plasma alanine appears to be a promising and reliable marker reflecting metabolic control in GSD-I patients.

Challenges of Gene Therapy for the Treatment of Glycogen Storage Diseases Type I and Type III

Glycogen storage diseases (GSDs) type I (GSDI) and type III (GSDIII), the most frequent hepatic GSDs, are due to defects in glycogen metabolism, mainly in the liver. In addition to hypoglycemia and liver pathology, renal, myeloid, or muscle complications affect GSDI and GSDIII patients. Currently, patient management is based on dietary treatment preventing severe hypoglycemia and increasing the lifespan of patients. However, most of the patients develop long-term pathologies. In the past years, gene therapy for GSDI has generated proof of concept for hepatic GSDs. This resulted in a recent clinical trial of adeno-associated virus (AAV)-based gene replacement for GSDIa. However, the current limitations of AAV-mediated gene transfer still represent a challenge for successful gene therapy in GSDI and GSDIII. Indeed, transgene loss over time was observed in GSDI liver, possibly due to the degeneration of hepatocytes underlying the physiopathology of both GSDI and GSDIII and leading to hepatic tumor development. Moreover, multitissue targeting requires high vector doses to target nonpermissive tissues such as muscle and kidney. Interestingly, recent pharmacological interventions or dietary regimen aiming at the amelioration of the hepatocyte abnormalities before the administration of gene therapy demonstrated improved efficacy in GSDs. In this review, we describe the advances in gene therapy and the limitations to be overcome to achieve efficient and safe gene transfer in GSDs.

Gene therapy prevents hepatic tumor initiation in murine glycogen storage disease type Ia at the tumor-developing stage

Hepatocellular adenoma/carcinoma (HCA/HCC) is a long-term complication of glycogen storage disease type-Ia (GSD-Ia), which is caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC), a key enzyme in gluconeogenesis. Currently, there is no therapy to address HCA/HCC in GSD-Ia. We have previously shown that a recombinant adeno-associated virus (rAAV) vector-mediated G6PC gene transfer to 2-week-old G6pc-/- mice prevents HCA development. However, it remains unclear whether G6PC gene transfer at the tumor developing stage of GSD-Ia can prevent tumor initiation or abrogate the pre-existing tumors. Using liver-specific G6pc-knockout (L-G6pc-/-) mice that develop HCA/HCC, we now show that treating the mice at the tumor-developing stage with rAAV-G6PC restores hepatic G6Pase-α expression, normalizes glucose homeostasis, and prevents de novo HCA/HCC development. The rAAV-G6PC treatment also normalizes defective hepatic autophagy and corrects metabolic abnormalities in the nontumor liver tissues of both tumor-free and tumor-bearing mice. However, gene therapy cannot restore G6Pase-α expression in the HCA/HCC lesions and fails to abrogate any pre-existing tumors. We show that the expression of 11 β-hydroxysteroid dehydrogenase type-1 that mediates local glucocorticoid activation is downregulated in HCA/HCC lesions, leading to impairment in glucocorticoid signaling critical for gluconeogenesis activation. This suggests that local glucocorticoid action downregulation in the HCA/HCC lesions may suppress gene therapy mediated G6Pase-α restoration. Collectively, our data show that rAAV-mediated gene therapy can prevent de novo HCA/HCC development in L-G6pc-/- mice at the tumor developing stage, but it cannot reduce any pre-existing tumor burden.

A Novel Mutation in a Newborn Baby Leading to Glycogen Storage Disease Type Ia

Glycogen storage disease type Ia (GSD1A) is caused by mutations in the G6PC gene. The G6PC gene was first cloned in 1993. Since then, many different mutations have been identified leading to this disease. Hepatomegaly is one of the important clinical manifestations of the disease. A 23-day-old girl was admitted to the hospital due to respiratory distress. Her physical examination was normal except for tachypnea. She had hypoglycemia, lactic academia, hyperlipidemia and hyperuricemia. With these clinical findings, GSD1A was considered in the patient and the diagnosis was genetically confirmed. By direct sequencing of the G6PC gene, we identified a novel homozygous variation (c.137T>G/p.Leu46Arg) in the patient and the healthy mother and father were heterozygotes for the variant. Here we present a case with a novel homozygous missense mutation c.137T>G/p.Leu46Arg in the G6PC gene leading to GSD1A clinical findings except early hepatomegaly. These findings expand the spectrum of causative mutations, and clinical findings in GSD1A.

Polycystic kidney features of the renal pathology in glycogen storage disease type I: possible evolution to renal neoplasia

Glycogen storage disease type I (GSDI) is a rare genetic pathology characterized by glucose-6 phosphatase (G6Pase) deficiency, translating in hypoglycemia during short fasts. Besides metabolic perturbations, GSDI patients develop long-term complications, especially chronic kidney disease (CKD). In GSDI patients, CKD is characterized by an accumulation of glycogen and lipids in kidneys, leading to a gradual decline in renal function. At a molecular level, the activation of the renin-angiotensin system is responsible for the development of renal fibrosis, eventually leading to renal failure. The same CKD phenotype was observed in a mouse model with a kidney-specific G6Pase deficiency (K.G6pc-/- mice). Furthermore, GSDI patients and mice develop frequently renal cysts at late stages of the nephropathy, classifying GSDI as a potential polycystic kidney disease (PKD). PKDs are genetic disorders characterized by multiple renal cyst formation, frequently caused by the loss of expression of polycystic kidney genes, such as PKD1/2 and PKHD1. Interestingly, these genes are deregulated in K.G6pc-/- kidneys, suggesting their possible role in GSDI cystogenesis. Finally, renal cysts are known to predispose to renal malignancy development. In addition, HNF1B loss is a malignancy prediction factor. Interestingly, Hnf1b expression was decreased in K.G6pc-/- kidneys. While a single case of renal cancer has been reported in a GSDI patient, a clear cell renal carcinoma was recently observed in one K.G6pc-/- mouse (out of 36 studied mice) at a later stage of the disease. This finding highlights the need to further analyze renal cyst development in GSDI patients in order to evaluate the possible associated risk of carcinogenesis, even if the risk might be limited.

Long-term safety and efficacy of AAV gene therapy in the canine model of glycogen storage disease type Ia

BACKGROUND

Viral mediated gene therapy has progressed after overcoming early failures, and gene therapy has now been approved for several conditions in Europe and the USA. Glycogen storage disease (GSD) type Ia, caused by a deficiency of glucose-6-phosphatase-α, has been viewed as an outstanding candidate for gene therapy. This follow-up report describes the long-term outcome for the naturally occurring GSD-Ia dogs treated with rAAV-GPE-hG6PC-mediated gene therapy.

METHODS

A total of seven dogs were treated with rAAV-GPE-hG6PC-mediated gene therapy. The first four dogs were treated at birth, and three dogs were treated between 2 and 6 months of age to assess the efficacy and safety in animals with mature livers. Blood and urine samples, radiographic studies, histological evaluation, and biodistribution were assessed.

RESULTS

Gene therapy improved survival in the GSD-Ia dogs. With treatment, the biochemical studies normalized for the duration of the study (up to 7 years). None of the rAAV-GPE-hG6PC-treated dogs had focal hepatic lesions or renal abnormalities. Dogs treated at birth required a second dose of rAAV after 2-4 months; gene therapy after hepatic maturation resulted in improved efficacy after a single dose.

CONCLUSION

rAAV-GPE-hG6PC treatment in GSD-Ia dogs was found to be safe and efficacious. GSD-Ia is an attractive target for human gene therapy since it is a monogenic disorder with limited tissue involvement. Blood glucose and lactate monitoring can be used to assess effectiveness and as a biomarker of success. GSD-Ia can also serve as a model for other hepatic monogenic disorders.