A female patient with GSD IXc developing multiple and recurrent hepatocellular carcinoma: a case report and literature review

Understanding Glycogen Storage Disease Type IX: A Systematic Review with Clinical Focus-Why It Is Not Benign and Requires Vigilance

BACKGROUND/OBJECTIVES

Glycogen storage disease type IX (GSD IX) is a group of inherited metabolic disorders caused by phosphorylase kinase deficiency affecting the liver or muscle. Despite being relatively common among GSDs, GSD IX remains underexplored.

METHODS

A systematic review of GSD IX was conducted per PRISMA guidelines using SCOPUS and PubMed, registered with PROSPERO. Inclusion focused on human clinical studies published up to 31 December 2024.

RESULTS

A total of 400 patients with GSD IX were analyzed: 274 IXa (mean age at diagnosis 5.1 years), 72 IXc (mean age at diagnosis 4.9 years), 39 IXb (mean age at diagnosis 4.2 years), and 15 IXd (mean age at diagnosis 44.9 years). Hepatomegaly was commonly reported in types IXa, IXb, and especially IXc (91.7%), but was rare in IXd. Elevated transaminases were frequently observed in types IXa, IXb, and particularly IXc, while uncommon in IXd. Fasting hypoglycemia was occasionally observed in types IXa and IXb, more frequently in IXc (52.7%), and was not reported in IXd. Growth delay or short stature was observed in a substantial proportion of patients with types IXa (43.8%), IXb, and IXc, but was rare in IXd. Muscle involvement was prominent in IXd, with all patients showing elevated CPK (mean 1011 U/L). Neurological involvement was infrequently reported in types IXa and IXc.

CONCLUSIONS

This systematic review includes the most extensive clinical case history of GSD IX described in the literature. The clinical spectrum of GSD IX varies widely among subtypes, with IXc being the most aggressive. While liver forms are generally present in early childhood, muscle-type IXd shows delayed onset and milder symptoms, often leading to diagnostic delays. For diagnosis, it is essential not to underestimate key clinical features such as hepatic involvement and hypoglycemia in a child under 5 years of age. Other manifestations, including the as-yet unexplored systemic involvement of bone and kidney, remain insufficiently understood and require further investigation. Next-generation sequencing has improved diagnostic precision over traditional biopsy. Dietary management, including uncooked cornstarch, Glycosade®, and high-protein intake, remains the cornerstone of treatment. However, there is a paucity of well-designed, evidence-based studies to determine the most effective therapeutic approach. Despite its historically perceived benign course, the broad phenotypic variability of GSD IX, including progressive liver involvement and potential neurological complications, highlights its substantial clinical relevance and underscores the need for accurate diagnostic classification and long-term multidisciplinary follow-up.

Glycogen storage disorder types IX: the mutation spectrum and ethnic distribution

Glycogen storage disorders (GSD) GSD-IX are characterized by deficiencies in muscular and/or hepatic phosphorylase enzymes. GSD type IX za is an X-linked disorder, while IXb and IXc are autosomal recessive disorders resulting from pathogenic variants in the genes encoding the Phosphorylase b Kinase regulatory subunit alpha (PHKA), beta (PHKB), and gamma (PHKG), respectively. Despite progress in understanding these diseases, there are still unclear questions regarding their clinical manifestations, genetic variations, and the relationship between genotype and phenotype. Therefore, this review focuses on variants of GSD IX subtypes and all clinical findings to establish a genotype-phenotype relationship as well as highlighting the wide spectrum of disease-causing variants. Such information is beneficial for the establishment of a privileged mutation screening process in a specific region or ethnic group. Diagnosis is based on clinical manifestations and laboratory test results, but molecular analysis is often necessary to distinguish the various forms with similar presentations.

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.

A Mouse Model of Glycogen Storage Disease Type IX-Beta: A Role for Phkb in Glycogenolysis

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.

Expanding the clinicopathological-genetic spectrum of glycogen storage disease type IXd by a Chinese neuromuscular center

Background

Glycogen storage disease (GSDs) is characterized by abnormally inherited glycogen metabolism. GSD IXd, which is caused by mutations in the PHKA1 gene, is an X-linked rare disease with mild myopathic symptoms. To date, only 13 patients with GSD IXd have been reported. In this study, we aimed to expand the clinicopathological-genetic spectrum of GSD IXd at a neuromuscular center in China.

Methods

Data on patients diagnosed with GSD IXd at our neuromuscular center were collected retrospectively. Clinical features, electrophysiology, muscle pathology, and genetic information were analyzed.

Results

Between 2015 and 2021, three patients were diagnosed with GSD IXd based on clinical manifestations, pathological findings, and genetic testing. One patient presented with mitochondrial myopathy. All patients exhibited muscle weakness and elevated levels of creatine kinase. Electromyography-detected myopathic changes were found in two patients, whereas one patient refused to undergo this examination. Pathological examinations in all patients revealed subsarcolemmal accumulation of glycogen under PAS staining. All patients had mutations in the PHKA1 gene and the patient with mitochondrial myopathy also had a mutation in the MT-TL1 gene.

Conclusion

Our study expands the clinicogenotype and phenotype of GSD IXd in a Chinese population. Our study also expands the known mutation spectrum for GSD IXd, contributing to a better characterization and understanding of this ultrarare neuromuscular disorder.