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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Medical Genetics · Glycogen Storage Disease Type I

How GSD I Works in the Body

At a Glance

Glycogen Storage Disease Type I (GSD I) occurs when the body lacks the functional glucose-6-phosphatase enzyme needed to release stored sugar from the liver. This causes the liver to swell with trapped glycogen, leading to dangerously low blood sugar, high lactic acid, and elevated lipids.

To understand Glycogen Storage Disease Type I (GSD I), it helps to think of the liver as a warehouse that stores energy for the body. In a typical person, the liver takes in extra sugar from meals and stores it as glycogen. When the body hasn’t eaten for a few hours, the liver “unlocks” that warehouse, turns the glycogen back into glucose (sugar), and releases it into the blood [1].

The Broken Switch

In GSD I, the body is missing a critical “switch” or “key” called glucose-6-phosphatase (G6Pase) [2]. This enzyme is responsible for the final step of releasing glucose into the bloodstream [3].

  • GSD Ia (von Gierke disease): The body cannot make the enzyme because of a mutation in the G6PC1 gene [4].
  • GSD Ib: The body makes the enzyme, but the “transport truck” (the G6PT protein, from the SLC37A4 gene) that brings the sugar to the enzyme is broken [5][6].

Without this switch, the liver can still store sugar, but it can never release it [1]. The “warehouse” becomes overstuffed with glycogen it cannot use, which is why the liver becomes physically enlarged (hepatomegaly) [3][7].

The Metabolic Domino Effect

When the body’s main energy path is blocked, it begins to “panic” and tries to find other ways to create fuel. This redirection causes the three hallmark metabolic imbalances of GSD I:

  1. Lactic Acidosis (High Lactate): Because the sugar (glucose-6-phosphate) is stuck inside the liver cells, the body tries to process it through an alternative pathway called glycolysis [1]. This creates a massive buildup of lactate (lactic acid) in the blood [8].
  2. Hyperlipidemia (High Fats/Triglycerides): The excess sugar is also diverted into a process called de novo lipogenesis—literally “new fat creation” [9]. This leads to very high levels of triglycerides, although cholesterol is typically only mildly elevated [10][11]. The extreme triglycerides can often appear as “milky” blood in laboratory samples.
  3. Hyperuricemia (High Uric Acid): The chemical backup in the liver also speeds up the production of uric acid [12]. If left untreated, this can lead to symptoms similar to gout or cause kidney stones later in life [13].

Making the Diagnosis

Doctors confirm GSD I using two main sets of data:

  • Biochemical Hallmarks: Finding the combination of low blood sugar (hypoglycemia) paired with high lactate, high uric acid, and high lipids [8][3].
  • Molecular Diagnosis: Genetic testing is now the “gold standard” [2]. By identifying mutations in the G6PC1 or SLC37A4 genes, doctors can confirm the diagnosis and the specific subtype without needing a liver biopsy [4][6].

What GSD I Is Not

Because GSD I is rare, it is sometimes confused with other conditions. It is important to distinguish it from:

  • GSD IX: A milder form of glycogen storage disease that does not typically cause severe lactic acidosis [14].
  • Glycogenic Hepatopathy: A condition seen in people with poorly controlled Type 1 Diabetes, where the liver swells with glycogen due to too much sugar and insulin, rather than a missing enzyme [7][15].
  • HLH (Hemophagocytic lymphohistiocytosis): A severe immune system overreaction that can cause an enlarged liver and low blood counts, occasionally mimicking the presentation of GSD Ib [16].

Common questions in this guide

What causes Glycogen Storage Disease Type I?
GSD I is caused by a missing or defective enzyme called glucose-6-phosphatase (G6Pase), or its transport protein. This defect prevents the liver from releasing stored sugar into the bloodstream, causing dangerously low blood sugar and liver enlargement.
What is the difference between GSD Ia and GSD Ib?
GSD Ia is caused by a mutation in the G6PC1 gene, meaning the body cannot produce the G6Pase enzyme. GSD Ib is caused by a mutation in the SLC37A4 gene, meaning the enzyme is present but the transport protein that moves sugar to it is broken.
Why does GSD I cause high triglycerides and lactic acid?
Because sugar gets trapped in the liver cells, the body attempts to process it through alternative pathways to survive. This redirection leads to an overproduction of lactic acid and the creation of new fat, causing high triglyceride levels in the blood.
How is GSD I diagnosed?
Doctors typically diagnose GSD I by observing biochemical hallmarks like low blood sugar paired with high lactate, high uric acid, and elevated lipids. The diagnosis is officially confirmed using genetic testing to identify specific gene mutations.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which specific gene mutation was found in our child's genetic testing—G6PC (Type Ia) or SLC37A4 (Type Ib)?
  2. 2.How high were our child's lactate and uric acid levels at diagnosis, and what are our target ranges for these during treatment?
  3. 3.Can you explain how 'de novo lipogenesis' is causing our child's high triglycerides?
  4. 4.If our child is in 'good metabolic control,' will their lactate and uric acid levels automatically return to normal?
  5. 5.Were other conditions like GSD IX, HLH, or glycogenic hepatopathy ruled out before this diagnosis?

Questions For You

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References

References (16)
  1. 1

    Fluorodeoxyglucose-positron emission tomography as a potential alternative tool for functional diagnosis of glycogen storage disease type I.

    Sato T, Inokuchi M, Nakano S, et al.

    Radiology case reports 2023; (18(1)):91-93 doi:10.1016/j.radcr.2022.09.084.

    PMID: 36324837
  2. 2

    Genome editing using Staphylococcus aureus Cas9 in a canine model of glycogen storage disease Ia.

    Arnson B, Kang HR, Brooks ED, et al.

    Molecular therapy. Methods & clinical development 2023; (29()):108-119 doi:10.1016/j.omtm.2023.03.001.

    PMID: 37021039
  3. 3

    Glucose-6 Phosphate, A Central Hub for Liver Carbohydrate Metabolism.

    Rajas F, Gautier-Stein A, Mithieux G

    Metabolites 2019; (9(12)) doi:10.3390/metabo9120282.

    PMID: 31756997
  4. 4

    The role of glucose-6-phosphatase activity in glucose homeostasis and its potential for diabetes therapy.

    Tan LS, Lau HH, Abdelalim EM, et al.

    Trends in molecular medicine 2025; (31(2)):152-164 doi:10.1016/j.molmed.2024.09.005.

    PMID: 39426930
  5. 5

    Structural basis of G6P/Pi transport and inhibition in SLC37A4.

    Zhou D, Zhang Y, Chen N, et al.

    Nature structural & molecular biology 2025; doi:10.1038/s41594-025-01711-5.

    PMID: 41225049
  6. 6

    Mutation analysis of SLC37A4 in a patient with glycogen storage disease-type Ib.

    Zhang Y, Sun H, Wan N

    The Journal of international medical research 2019; (47(12)):5996-6003 doi:10.1177/0300060519867819.

    PMID: 31617422
  7. 7

    Computed Tomography and Magnetic Resonance Imaging Features of Primary and Secondary Hepatic Glycogenosis.

    Chen ZY, Liu YP, Zheng GJ

    Annals of hepatology 2018; (17(6)):903-905 doi:10.5604/01.3001.0012.7189.

    PMID: 30600303
  8. 8

    Recoverable, Record-High Lactic Acidosis in a Patient with Glycogen Storage Disease Type 1: A Mixed Type A and Type B Lactate Disorder.

    Oster Y, Wexler ID, Heyman SN, Fried E

    Case reports in medicine 2016; (2016()):4362743 doi:10.1155/2016/4362743.

    PMID: 27974893
  9. 9

    Hepatic Carbohydrate Response Element Binding Protein Activation Limits Nonalcoholic Fatty Liver Disease Development in a Mouse Model for Glycogen Storage Disease Type 1a.

    Lei Y, Hoogerland JA, Bloks VW, et al.

    Hepatology (Baltimore, Md.) 2020; (72(5)):1638-1653 doi:10.1002/hep.31198.

    PMID: 32083759
  10. 10

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

    Hoogerland JA, Peeks F, Hijmans BS, et al.

    Journal of inherited metabolic disease 2021; (44(4)):879-892 doi:10.1002/jimd.12380.

    PMID: 33739445
  11. 11

    The absence of hepatic glucose-6 phosphatase/ChREBP couple is incompatible with survival in mice.

    Rajas F, Dentin R, Cannella Miliano A, et al.

    Molecular metabolism 2021; (43()):101108 doi:10.1016/j.molmet.2020.101108.

    PMID: 33137488
  12. 12

    Mutational analysis and clinical investigations of medically diagnosed GSD 1a patients from Pakistan.

    Gul B, Firasat S, Shan T, et al.

    PloS one 2023; (18(11)):e0288965 doi:10.1371/journal.pone.0288965.

    PMID: 38033126
  13. 13

    [Advances on the management of renal lesion in glycogen storage disease type I].

    Wu WC, Wang JS

    Zhonghua gan zang bing za zhi = Zhonghua ganzangbing zazhi = Chinese journal of hepatology 2021; (29(1)):75-78 doi:10.3760/cma.j.cn501113-20201230-00687.

    PMID: 33541027
  14. 14

    Hepatic Glycogenosis In Children: Spectrum Of Presentation And Diagnostic Modalities.

    Bilal H, Cheema HA, Fayyaz Z, et al.

    Journal of Ayub Medical College, Abbottabad : JAMC 2019; (31(3)):368-371.

    PMID: 31535508
  15. 15

    Hepatopathy Associated With Type 1 Diabetes: Distinguishing Non-alcoholic Fatty Liver Disease From Glycogenic Hepatopathy.

    Mertens J, De Block C, Spinhoven M, et al.

    Frontiers in pharmacology 2021; (12()):768576 doi:10.3389/fphar.2021.768576.

    PMID: 34759828
  16. 16

    Glycogen storage disorder-mimicking presentation of X-linked lymphoproliferative syndrome (XLP).

    Elangovan A, Bali A, Vellingiri B, Wander A

    BMJ case reports 2025; (18(12)) doi:10.1136/bcr-2025-265290.

    PMID: 41475861

This page explains the metabolic mechanisms of GSD I for educational purposes. Always consult your child's metabolic geneticist or pediatrician for personalized medical advice and disease management.

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