Browsing by Subject "Glycogen Storage Disease"

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    Characterization of liver GSD IX γ2 pathophysiology in a novel Phkg2-/- mouse model.
    (Molecular genetics and metabolism, 2021-07) Gibson, Rebecca A; Lim, Jeong-A; Choi, Su Jin; Flores, Leticia; Clinton, Lani; Bali, Deeksha; Young, Sarah; Asokan, Aravind; Sun, Baodong; Kishnani, Priya S

    Introduction

    Liver Glycogen Storage Disease IX is a rare metabolic disorder of glycogen metabolism caused by deficiency of the phosphorylase kinase enzyme (PhK). Variants in the PHKG2 gene, encoding the liver-specific catalytic γ2 subunit of PhK, are associated with a liver GSD IX subtype known as PHKG2 GSD IX or GSD IX γ2. There is emerging evidence that patients with GSD IX γ2 can develop severe and progressive liver disease, yet research regarding the disease has been minimal to date. Here we characterize the first mouse model of liver GSD IX γ2.

    Methods

    A Phkg2-/- mouse model was generated via targeted removal of the Phkg2 gene. Knockout (Phkg2-/-, KO) and wild type (Phkg2+/+, WT) mice up to 3 months of age were compared for morphology, Phkg2 transcription, PhK enzyme activity, glycogen content, histology, serum liver markers, and urinary glucose tetrasaccharide Glcα1-6Glcα1-4Glcα1-4Glc (Glc4).

    Results

    When compared to WT controls, KO mice demonstrated significantly decreased liver PhK enzyme activity, increased liver: body weight ratio, and increased glycogen in the liver, with no glycogen accumulation observed in the brain, quadricep, kidney, and heart. KO mice demonstrated elevated liver blood markers as well as elevated urine Glc4, a commonly used biomarker for glycogen storage disease. KO mice demonstrated features of liver structural damage. Hematoxylin & Eosin and Masson's Trichrome stained KO mice liver histology slides revealed characteristic GSD hepatocyte architectural changes and early liver fibrosis, as have been reported in liver GSD patients.

    Discussion

    This study provides the first evidence of a mouse model that recapitulates the liver-specific pathology of patients with GSD IX γ2. The model will provide the first platform for further study of disease progression in GSD IX γ2 as well as for the evaluation of novel therapeutics.
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    Every Three Hours
    (2020-12-14) Shaw, Janet
    Every Three Hours is a memoir about raising my son Patrick who has two rare medical conditions--Glycogen Storage Disease 1a (GSD1a) and Mast Cell Activation Syndrome (MCAS). As I analyze the events in Patrick’s life when my spouse and I educated and nurtured him, it raises the central question for my research: how can parents of chronically ill children foster safety and independence for their children? This master’s project is multi-disciplinary in that it incorporates primary and secondary data as well as creative writing. Using first-person narrative, I explore how my husband and I navigated the uncharted medical and parenting challenges of GSD1a and MCAS. Secondly, woven into this primary research is data exploring the medical and psychological aspects of GSD and MCAS. Additional insights come from memoirs of parents who have walked down a similar road. As I chronicled Patrick’s life, I realized that this project has become not only a story of raising an ill child to become independent. This memoir has become an awareness of life choices I had to make once I had a compromised child. This memoir is also about my false sense of control as a young adult and the loss of that control. Additionally, this account acknowledges that almost all parents love their chronically ill children and only want the best for them. The reality of raising an ill child is that it takes health insurance and money—not moral superiority.
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    Gene therapy for glycogen storage diseases.
    (Human molecular genetics, 2019-10) Kishnani, Priya S; Sun, Baodong; Koeberl, Dwight D
    The focus of this review is the development of gene therapy for glycogen storage diseases (GSDs). GSD results from the deficiency of specific enzymes involved in the storage and retrieval of glucose in the body. Broadly, GSDs can be divided into types that affect liver or muscle or both tissues. For example, glucose-6-phosphatase (G6Pase) deficiency in GSD type Ia (GSD Ia) affects primarily the liver and kidney, while acid α-glucosidase (GAA) deficiency in GSD II causes primarily muscle disease. The lack of specific therapy for the GSDs has driven efforts to develop new therapies for these conditions. Gene therapy needs to replace deficient enzymes in target tissues, which has guided the planning of gene therapy experiments. Gene therapy with adeno-associated virus (AAV) vectors has demonstrated appropriate tropism for target tissues, including the liver, heart and skeletal muscle in animal models for GSD. AAV vectors transduced liver and kidney in GSD Ia and striated muscle in GSD II mice to replace the deficient enzyme in each disease. Gene therapy has been advanced to early phase clinical trials for the replacement of G6Pase in GSD Ia and GAA in GSD II (Pompe disease). Other GSDs have been treated in proof-of-concept studies, including GSD III, IV and V. The future of gene therapy appears promising for the GSDs, promising to provide more efficacious therapy for these disorders in the foreseeable future.
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    Novel AAV Based Genome Editing Therapies for Glycogen Storage Disease Type Ia
    (2023) Arnson, Benjamin Donald

    Glycogen storage disease type Ia (GSD Ia) is an autosomal recessive metabolicdisorder caused deficiency of glucose-6-phosphatase (G6Pase) resulting from pathogenic variants in the G6PC gene. G6Pase catalyzes the hydrolysis of glucose-6-phosphate to release glucose which can then enter the bloodstream. GSD Ia patients have excess glycogen accumulation mainly in the liver and kidneys and suffer from life threatening hypoglycemia. The current treatment for GSD Ia is dietary therapy that requires patients to frequently consume uncooked cornstarch on a strict schedule. Cornstarch provides a complex carbohydrate that slowly releases glucose to prevent hypoglycemia. This treatment fails to prevent long-term complications associated with GSD Ia including renal failure and the development of hepatocellular adenomas and carcinomas. This lab and others have developed adeno-associated virus (AAV) vector based gene therapies to deliver and therapeutic G6PC transgene to affected tissues in GSD Ia animal models. However, the therapeutic effect is limited as AAV vector genomes are rapidly lost and the biochemical correction declines. Currently no treatment for GSD Ia exists that provides stable, robust expression of G6Pase that can clear glycogen and prevent hypoglycemia. This study employed a novel genome editing approach designed to insert the therapeutic G6PC into the endogenous locus in canine and murine models of GSD Ia. Integration of the transgene into the genome will promote stable expression of G6Pase and prevent the decline of vector genomes and the therapeutic benefit. This genome editing approach utilizes the CRISPR/Cas9 system to generated targeted double stranded DNA breaks at a targeted site in the genome. The G6PC transgene is present in a Donor template with homology to the DNA break to drive homology directed repair (HDR) resulting in the integration of the transgene into the genome. In a canine model of GSD Ia, editing and incorporation of the transgene was achieved in both adult dogs and puppies. Up to 1.0% of alleles were edited in the dog livers and contained the transgene. G6Pase production from the integrated transgene was detected, which correlated with prevention of hypoglycemia during fasting. This demonstrated genome editing in the liver of a large animal model for an inherited metabolic disorder using HDR to insert a therapeutic transgene. A subsequent study in GSD Ia mice also showed incorporation of a G6PC transgene in the mouse genome. Mice were treated with either the Donor transgene vector alone or with both the Donor and a CRISPR/Cas9 vector to assess to role of nuclease activity on integration. Mice treated with both vectors demonstrated improved blood glucose concentrations during fasting, decreased liver glycogen, and increased vector genome copies. Treatment with the pan PPAR agonist bezafibrate increased the efficiency of genome editing. Mice treated with bezafibrate that received both editing vectors had 5.9% of alleles that contained the integrated transgene, whereas only 3.1% of alleles contained the transgene in mice not treated with the drug. This work showed that integration of a therapeutic transgene using CRISPR/Cas9 based genome editing is possible in murine and canine models of GSD Ia. Editing resulted in biochemical correction and sustained transgene expression. These data support the further development of genome editing technologies for GSD Ia and other inherited metabolic disorders.

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    Preclinical Development of New Therapy for Glycogen Storage Diseases.
    (Curr Gene Ther, 2015) Sun, Baodong; Brooks, Elizabeth D; Koeberl, Dwight D
    Glycogen storage disease (GSD) consists of more than 10 discrete conditions for which the biochemical and genetic bases have been determined, and new therapies have been under development for several of these conditions. Gene therapy research has generated proof-of-concept for GSD types I (von Gierke disease) and II (Pompe disease). Key features of these gene therapy strategies include the choice of vector and regulatory cassette, and recently adeno-associated virus (AAV) vectors containing tissue-specific promoters have achieved a high degree of efficacy. Efficacy of gene therapy for Pompe disease depend upon the induction of immune tolerance to the therapeutic enzyme. Efficacy of von Gierke disease is transient, waning gradually over the months following vector administration. Small molecule therapies have been evaluated with the goal of improving standard of care therapy or ameliorating the cellular abnormalities associated with specific GSDs. The receptor-mediated uptake of the therapeutic enzyme in Pompe disease was enhanced by administration of β2 agonists. Rapamycin reduced the liver fibrosis observed in GSD III. Further development of gene therapy could provide curative therapy for patients with GSD, if efficacy from preclinical research is observed in future clinical trials and these treatments become clinically available.