Glycogen Storage disease, type 0 : GYS2 Sequencing

Test Information

GYS2 sequencing is a molecular test used to identify variants in the gene associated with Glycogen Storage disease, type 0.

Turnaround Time

3 weeks

CPT Code(s)





  • GYS2

Clinical Information

Glycogen synthase deficiency, or glycogen storage disease type 0, is caused by mutations in the GYS2 gene that prevent the synthesis of glycogen in the liver. Symptoms of this condition usually appear in infancy or early childhood, and they include fasting hypoglycemia, ketosis, and low levels of lactate and alanine in blood. Hyperglycemia and hyperlacticacidemia often occur after eating. Some individuals with glycogen synthase deficiency may be relatively asymptomatic with occasional episodes of fasting hypoglycemia, while others may experience recurrent fatigue and vomiting, particularly during periods of fasting or illness. Severe episodes of hypoglycemia may present with pallor, drowsiness, confusion, seizures, and ultimately coma if left untreated. Muscle cramping, exercise intolerance, and minor growth delays may occur, but intelligence is generally not affected. Unlike many storage conditions, glycogen levels are decreased in the liver, so hepatomegaly is typically absent. Most symptoms can be relieved by dietary intervention. Glycogen synthase deficiency is inherited as an autosomal recessive condition and is believed to be significantly underdiagnosed.


Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutations within a family to allow for carrier testing and prenatal diagnosis.


Sanger Sequencing

Specimen Requirements

The preferred sample type is peripheral blood collected in an EDTA (purple top) tube - at least 2-3ml for pediatric patients and 5-6ml for adult patients. Extracted DNA, dried blood spots, and saliva are also accepted for this test. Saliva samples must be submitted in an approved saliva kit. Contact the lab to receive a saliva kit or to have one sent to your patient.

Transport Instructions

The specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.

Prenatal Testing Information

Prenatal diagnosis is available if the familial mutations are known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory prior to sending a prenatal specimen.

Have Questions? Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Falecia Thomas, MS, CGC

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