GYS2 gene

Also known as: GSD0a; Hypoglycemia with deficiency of glycogen synthetase in the liver; liver glycogen synthase deficiency; Liver glycogen storage disease 0, GSD 0a.


1. The Disease:

A genetically inherited anomaly of glycogen metabolism and a form of glycogen storage disease (GSD) characterized by fasting hypoglycemia. This is not a glycogenosis, strictly speaking, as the enzyme deficiency decreases glycogen reserves.

2. The Symptoms:

Infants are asymptomatic at birth and in the neonatal period. Signs and symptoms typically begin in infancy or early childhood. Patients present with morning fatigue and fasting hypoglycemia (without hepatomegaly) associated with hyperketonemia but without hyperalaninemia or hyperlactacidemia. After meals, major hyperglycemia associated with lactate and alanine increase and hyperlipidemia is observed.Lack of early signs or symptoms does not exclude the diagnosis.

3. Actions to take in case of early diagnosis:

  • Infants with a positive genetic test (having 2 pathogenic variants or 2 copies of a single pathogenic variant in the gene GYS2) should continue breastfeeding, avoid fasting. Early treatment is essential in preventing chronic symptoms.
  • GSD 0a is a lifelong disease that requires regular evaluation by a metabolic physician and metabolic nutritionist to follow an specific diet that includes frequent meals with high protein intake during the day and addition of uncooked starch in the evening.
  • Prognosis is favorable when the disease is correctly managed.
  • Genetic counseling is highly recommended for family planning and evaluation of at-risk family members such as siblings.

4. For more information



  • Kamenets EA, Gusarova EA, Milovanova NV, et al. Hepatic glycogen synthase (GYS2) deficiency: seven novel patients and seven novel variants. JIMD Rep. 2020; 53(1):39-44. PMID: 32395408.
  • Arko JJ, Debeljak M, Tansek MZ, Battelino T, Groselj U. A patient with glycogen storage disease type 0 and a novel sequence variant in GYS2: a case report and literature review. J Int Med Res. 2020;48(8). PMID: 32779500.
  • Iijima H, Ago Y, Fujiki R, Takayanagi T, Kubota M. Novel GYS2 mutations in a Japanese patient with glycogen storage disease type 0a. Mol Genet Metab Rep. 2021; 26. PMID:33489759.