Alglucosidase alfa treatment alleviates liver disease in a mouse model of glycogen storage disease type IV

Clinical genetic analysis of an adult polyglucosan body disease (APBD) family caused by the compound heterozygous variant of GBE1 p.R156C and deletion exon 3-7

Introduction

Adult Polyglucosan Body Disease (APBD) is a rare, autosomal recessive neurodegenerative disorder that affects both the central and peripheral nervous systems. It is primarily caused by mutations in the Glycogen Branching Enzyme 1 (GBE1) gene. APBD is typically associated with Ashkenazi Jewish populations, though it can occur in other ethnic groups. This study aims to expand the phenotypic and genetic spectrum of APBD, particularly in non-Ashkenazi Jewish patients, and to identify atypical genetic alterations linked to the disease.

Methods

A 57-year-old Chinese male (Ⅱ3) presented with a 4-year history of progressive bladder dysfunction, upper and lower motor neuron impairment, sensory loss, and lower limb weakness, leading to difficulty with gait. Genetic testing was performed to identify potential pathogenic variants in the GBE1 gene. A family assessment revealed a sister (Ⅱ5) with the same clinical features. Both patients underwent genetic analysis, which included sequencing and deletion analysis.

Results

Genetic testing revealed that both affected individuals (Ⅱ3 and Ⅱ5) carried compound heterozygous variants in the GBE1 gene: c.466C>T (p.R156C) in exon 4 and a large deletion of exons 3-7. The two pathogenic variants co-segregated in the family, confirming the diagnosis of APBD in these individuals.

Discussion

This case expands the phenotypic and genetic spectrum of APBD, particularly by documenting its occurrence in non-Ashkenazi Jewish patients. Additionally, the identification of atypical genetic alterations, such as the large deletion in GBE1, provides new insights into the genetic basis of the disease and may aid in understanding its broader clinical manifestations. These findings suggest the need for a broader genetic screening approach in APBD diagnosis, especially in diverse populations.

Progressive liver disease and dysregulated glycogen metabolism in murine GSD IX γ2 models human disease

Hepatic glycogen storage disease type IX γ2 (GSD IX γ2) is a severe, liver-specific subtype of GSD IX. While all patients with hepatic GSD IX present with similar symptoms, over 95 % of patients with GSD IX γ2 progress to liver fibrosis and cirrhosis. Despite disease severity, the long-term natural history of GSD IX γ2 liver disease progression is not known. Our lab previously characterized the Phkg2-/- mouse model at 3 months of age, demonstrating that the mouse recapitulates the early liver disease phenotype of GSD IX γ2. To understand how liver disease progresses in GSD IX γ2, we characterized the mouse model through 24 months of age. Our study showed for the first time that GSD IX γ2 mice develop liver fibrosis that progresses to cirrhosis. Importantly, we observed that the progression of liver fibrosis is associated with an initial elevation and subsequent decrease of key GSD biomarkers - the latter being a finding that is often considered to be an improvement of disease in patients. In recognition of the unique liver fibrosis pattern and to support future therapeutic investigations using this model, we developed a novel scoring system for GSD IX γ2 mouse liver pathology. Lastly, this work introduces evidence of a dysregulated glycogen metabolism pathway which can serve as an endpoint for future therapeutic evaluation. As we await longitudinal clinical natural history data, these findings greatly expand our understanding of liver disease manifestations in GSD IX γ2 and have notable clinical applications.

Alleviation of a polyglucosan storage disorder by enhancement of autophagic glycogen catabolism

This work employs adult polyglucosan body disease (APBD) models to explore the efficacy and mechanism of action of the polyglucosan-reducing compound 144DG11. APBD is a glycogen storage disorder (GSD) caused by glycogen branching enzyme (GBE) deficiency causing accumulation of poorly branched glycogen inclusions called polyglucosans. 144DG11 improved survival and motor parameters in a GBE knockin (Gbeys/ys ) APBD mouse model. 144DG11 reduced polyglucosan and glycogen in brain, liver, heart, and peripheral nerve. Indirect calorimetry experiments revealed that 144DG11 increases carbohydrate burn at the expense of fat burn, suggesting metabolic mobilization of pathogenic polyglucosan. At the cellular level, 144DG11 increased glycolytic, mitochondrial, and total ATP production. The molecular target of 144DG11 is the lysosomal membrane protein LAMP1, whose interaction with the compound, similar to LAMP1 knockdown, enhanced autolysosomal degradation of glycogen and lysosomal acidification. 144DG11 also enhanced mitochondrial activity and modulated lysosomal features as revealed by bioenergetic, image-based phenotyping and proteomics analyses. As an effective lysosomal targeting therapy in a GSD model, 144DG11 could be developed into a safe and efficacious glycogen and lysosomal storage disease therapy.

The potential of dietary treatment in patients with glycogen storage disease type IV

There is paucity of literature on dietary treatment in glycogen storage disease (GSD) type IV and formal guidelines are not available. Traditionally, liver transplantation was considered the only treatment option for GSD IV. In light of the success of dietary treatment for the other hepatic forms of GSD, we have initiated this observational study to assess the outcomes of medical diets, which limit the accumulation of glycogen. Clinical, dietary, laboratory, and imaging data for 15 GSD IV patients from three centres are presented. Medical diets may have the potential to delay or prevent liver transplantation, improve growth and normalize serum aminotransferases. Individual care plans aim to avoid both hyperglycaemia, hypoglycaemia and/or hyperketosis, to minimize glycogen accumulation and catabolism, respectively. Multidisciplinary monitoring includes balancing between traditional markers of metabolic control (ie, growth, liver size, serum aminotransferases, glucose homeostasis, lactate, and ketones), liver function (ie, synthesis, bile flow and detoxification of protein), and symptoms and signs of portal hypertension.