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GYS1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

GYS1 gene

The GYS1 gene provides instructions for making muscle glycogen synthase, an enzyme essential for storing energy in cardiac and skeletal muscles.

Normal Function

The GYS1 gene provides instructions for making an enzyme called muscle glycogen synthase. This enzyme is produced in most cells but is most abundant in heart (cardiac) muscle and muscles used for movement (skeletal muscles). Muscle glycogen synthase helps link together molecules of the simple sugar glucose to form the complex sugar glycogen, which is a major source of stored energy in the body.

Most glucose taken in from food is stored as glycogen in muscle cells. During contractions of the cardiac muscle or rapid or sustained movement of skeletal muscle, glycogen stored in muscle cells is broken down to supply the cells with energy.

Health Conditions Related to Genetic Changes

Glycogen storage disease type 0

At least four mutations in the GYS1 gene have been found to cause a form of glycogen storage disease type 0 (GSD 0) that affects cardiac and skeletal muscle. Most GYS1 gene mutations that cause this condition lead to a lack of functional muscle glycogen synthase, resulting in a complete absence of glycogen in muscle cells.

Normally, glycogen is formed from the leftover glucose that is not immediately used by cells after meals. In people with GSD 0, who cannot form glycogen, the extra sugar is released by the body. As a result, individuals with muscle GSD 0 do not have any stored energy, which leads to:

  • Muscle pain
  • Weakness
  • Episodes of fainting following moderate physical activity

Since there is no glycogen in cardiac muscle, affected individuals are also at an increased risk of cardiac arrest and sudden death, particularly after physical activity.

Other Names for This Gene

  • glycogen [starch] synthase, muscle
  • glycogen synthase 1 (muscle)
  • GSY
  • GYS
  • GYS1_HUMAN
  • muscle glycogen synthase
  • muscle glycogen synthase 1

Genomic Location

The GYS1 gene is found on chromosome 19.

Frequently Asked Questions

definitive diagnosis requires a muscle biopsy showing markedly reduced or absent glycogen stores, coupled with an enzymatic assay demonstrating low muscle glycogen synthase activity. Genetic confirmation is achieved by sequencing the GYS1 gene to identify pathogenic variants; whole‑exome sequencing can also be used if the mutation is not found in targeted panels.
Frequent, small meals rich in complex carbohydrates and low in simple sugars help maintain steady glucose levels. A late‑night snack containing slowly digestible carbs (e.g., oatmeal or whole‑grain toast) can prevent overnight hypoglycemia. Some patients benefit from a continuous glucose monitor to guide dietary adjustments.
Key red flags include recurrent episodes of fainting or dizziness after mild exercise, unexplained muscle pain or weakness, and a history of hypoglycemia between meals. In infants, poor feeding, failure to thrive, or a sudden drop in blood glucose after a short fast are also suggestive.
Because cardiac muscle lacks glycogen, patients are at risk for arrhythmias and sudden cardiac arrest. Baseline ECG and echocardiography are recommended at diagnosis, followed by annual cardiac evaluations or sooner if symptoms such as palpitations, chest pain, or syncope occur. In high‑risk patients, ambulatory Holter monitoring may be indicated.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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