Mutations in the liver glycogen phosphorylase (Pygl) gene are associated with the diagnosis of glycogen storage disease type VI (GSD‐VI). To understand the pathogenesis of GSD‐VI, we generated a mouse model with Pygl deficiency (Pygl ^−/−). Pygl ^−/− mice exhibit hepatomegaly, excessive hepatic glycogen accumulation, and low hepatic free glucose along with lower fasting blood glucose levels and elevated blood ketone bodies. Hepatic glycogen accumulation in Pygl ^−/− mice increases with age. Masson's trichrome and picrosirius red staining revealed minimal to mild collagen deposition in periportal, subcapsular, and/or perisinusoidal areas in the livers of old Pygl ^−/− mice (>40 weeks). Consistently, immunohistochemical analysis showed the number of cells positive for alpha smooth muscle actin (α‐SMA), a marker of activated hepatic stellate cells, was increased in the livers of old Pygl ^−/− mice compared with those of age‐matched wild‐type (WT) mice. Furthermore, old Pygl ^−/− mice had inflammatory infiltrates associated with hepatic vessels in their livers along with up‐regulated hepatic messenger RNA levels of C‐C chemokine ligand 5 (Ccl5/Rantes) and monocyte chemoattractant protein 1 (Mcp‐1), indicating inflammation, while age‐matched WT mice did not. Serum levels of aspartate aminotransferase and alanine aminotransferase were elevated in old Pygl ^−/− mice, indicating liver damage. Conclusion: Pygl deficiency results in progressive accumulation of hepatic glycogen with age and liver damage, inflammation, and collagen deposition, which can increase the risk of liver fibrosis. Collectively, the Pygl‐deficient mouse recapitulates clinical features in patients with GSD‐VI and provides a model to elucidate the mechanisms underlying hepatic complications associated with defective glycogen metabolism.

In the last three decades, gene therapy has demonstrated significant progress. Over 700 active investigational new drug (IND) applications have been reported. Research on in utero gene therapy has advanced, but ethical and safety concerns persist. A novel approach under investigation is placental gene therapy, which holds promise for targeting diseases associated with placental dysfunction, such as fetal growth restriction (FGR) and preeclampsia. One of the underlying causes of placental insufficiency in these conditions is reduced placental growth factor-driven angiogenesis and endothelial cell dysfunction during fetal development. Studies have explored the overexpression of growth factor transgenes like IGF-1 to address FGR, yielding promising outcomes in animal models. Furthermore, intra-placental gene transfer, instead of systemic delivery of gene therapy vectors, has the potential to treat and cure these disorders. However, challenges and limitations akin to in utero gene therapy persist, including the risk of in utero infection, potential impairment of the mother’s future fertility, the risk of germline integration, and possible off-target effects of gene transfer in the fetus or the mother. Consequently, additional research and deliberation within the scientific and medical communities are warranted to fully comprehend the potential benefits and risks of placental gene therapy.

Glycogen storage disease type IX (GSD-IX) constitutes nearly a quarter of all GSDs. This ketotic form of GSD is caused by mutations in phosphorylase kinase (PhK), which is composed of four subunits (α, β, γ, δ). PhK is required for the activation of the liver isoform of glycogen phosphorylase (PYGL), which generates free glucose-1-phosphate monomers to be used as energy via cleavage of the α -(1,4) glycosidic linkages in glycogen chains. Mutations in any of the PhK subunits can negatively affect the regulatory and catalytic activity of PhK during glycogenolysis. To understand the pathogenesis of GSD-IX-beta, we characterized a newly created PHKB knockout (Phkb^−/−) mouse model. In this study, we assessed fasting blood glucose and ketone levels, serum metabolite concentrations, glycogen phosphorylase activity, and gene expression of gluconeogenic genes and fibrotic genes. Phkb^−/− mice displayed hepatomegaly with lower fasting blood glucose concentrations. Phkb^−/− mice showed partial liver glycogen phosphorylase activity and increased sensitivity to pyruvate, indicative of partial glycogenolytic activity and upregulation of gluconeogenesis. Additionally, gene expression analysis demonstrated increased lipid metabolism in Phkb^−/− mice. Gene expression analysis and liver histology in the livers of old Phkb^−/− mice (>40 weeks) showed minimal profibrogenic features when analyzed with age-matched wild-type (WT) mice. Collectively, the Phkb^−/− mouse recapitulates mild clinical features in patients with GSD-IX-beta. Metabolic and molecular analysis confirmed that Phkb^−/− mice were capable of sustaining energy homeostasis during prolonged fasting by using partial glycogenolysis, increased gluconeogenesis, and potentially fatty acid oxidation in the liver.

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.