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PYGL gene

glycogen phosphorylase L

Normal Function

The PYGL gene provides instructions for making an enzyme called liver glycogen phosphorylase. This enzyme breaks down a complex sugar called glycogen. Liver glycogen phosphorylase is one of three related enzymes that break down glycogen in cells; the other glycogen phosphorylases are found in the brain and in muscles. Liver glycogen phosphorylase is found only in liver cells, where it breaks down glycogen into a type of sugar called glucose-1-phosphate. Additional steps convert glucose-1-phosphate into glucose, a simple sugar that is the main energy source for most cells in the body.

Health Conditions Related to Genetic Changes

Glycogen storage disease type VI

At least 17 mutations in the PYGL gene have been found to cause glycogen storage disease type VI (GSDVI). Most mutations change single protein building blocks (amino acids) in liver glycogen phosphorylase, affecting the normal function of the enzyme. In the Old Order Mennonite population, a common mutation (written as 1620+1G>A) disrupts the way the PYGL gene's instructions are used to make the enzyme. A defective liver glycogen phosphorylase enzyme impairs the normal breakdown of glycogen. As a result, liver cells cannot use glycogen for energy, so liver function becomes impaired. A lack of glycogen breakdown within liver cells leads to the major features of GSDVI.

More About This Health Condition

Other Names for This Gene

  • glycogen phosphorylase, liver form
  • GSD6
  • phosphorylase, glycogen, liver

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Beauchamp NJ, Taybert J, Champion MP, Layet V, Heinz-Erian P, Dalton A, Tanner MS, Pronicka E, Sharrard MJ. High frequency of missense mutations in glycogen storage disease type VI. J Inherit Metab Dis. 2007 Oct;30(5):722-34. doi: 10.1007/s10545-007-0499-9. Epub 2007 Aug 21. Citation on PubMed
  • Burwinkel B, Bakker HD, Herschkovitz E, Moses SW, Shin YS, Kilimann MW. Mutations in the liver glycogen phosphorylase gene (PYGL) underlying glycogenosis type VI. Am J Hum Genet. 1998 Apr;62(4):785-91. doi: 10.1086/301790. Citation on PubMed or Free article on PubMed Central
  • Chang S, Rosenberg MJ, Morton H, Francomano CA, Biesecker LG. Identification of a mutation in liver glycogen phosphorylase in glycogen storage disease type VI. Hum Mol Genet. 1998 May;7(5):865-70. doi: 10.1093/hmg/7.5.865. Citation on PubMed
  • Labrador E, Weinstein DA. Glycogen Storage Disease Type VI. 2009 Apr 23 [updated 2019 Nov 27]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.