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PYGM gene

glycogen phosphorylase, muscle associated

Normal Function

The PYGM gene provides instructions for making an enzyme called myophosphorylase. This enzyme breaks down a complex sugar called glycogen. Myophosphorylase is one of three related enzymes called glycogen phosphorylases that break down glycogen in cells. Myophosphorylase is found only in muscle cells, where it breaks down glycogen into a simpler 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.

Health Conditions Related to Genetic Changes

Glycogen storage disease type V

Approximately 130 mutations in the PYGM gene have been found to cause glycogen storage disease type V (GSDV). One mutation that is common in North American and European populations is written as Arg50Ter or R50X. This mutation creates a premature stop signal in the instructions for making myophosphorylase, which decreases the production of the enzyme. A shortage of myophosphorylase impairs the normal breakdown of glycogen. Other mutations that cause GSDV may severely reduce enzyme activity or change the way the enzyme folds into a 3-dimensional shape. The defective enzyme is unable to break down glycogen. As a result, muscle cells cannot produce enough energy, so muscles become easily fatigued. Reduced energy production in muscle cells leads to the major features of GSDV.

More About This Health Condition

Other Names for This Gene

  • glycogen phosphorylase, muscle form
  • myophosphorylase
  • phosphorylase, glycogen, muscle

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


  • Aquaron R, Berge-Lefranc JL, Pellissier JF, Montfort MF, Mayan M, Figarella-Branger D, Coquet M, Serratrice G, Pouget J. Molecular characterization of myophosphorylase deficiency (McArdle disease) in 34 patients from Southern France: identification of 10 new mutations. Absence of genotype-phenotype correlation. Neuromuscul Disord. 2007 Mar;17(3):235-41. doi: 10.1016/j.nmd.2006.12.014. Epub 2007 Feb 26. Citation on PubMed
  • Bruno C, Cassandrini D, Martinuzzi A, Toscano A, Moggio M, Morandi L, Servidei S, Mongini T, Angelini C, Musumeci O, Comi GP, Lamperti C, Filosto M, Zara F, Minetti C. McArdle disease: the mutation spectrum of PYGM in a large Italian cohort. Hum Mutat. 2006 Jul;27(7):718. doi: 10.1002/humu.9434. Citation on PubMed
  • Deschauer M, Morgenroth A, Joshi PR, Glaser D, Chinnery PF, Aasly J, Schreiber H, Knape M, Zierz S, Vorgerd M. Analysis of spectrum and frequencies of mutations in McArdle disease. Identification of 13 novel mutations. J Neurol. 2007 Jun;254(6):797-802. doi: 10.1007/s00415-006-0447-x. Epub 2007 Apr 3. Citation on PubMed
  • Nogales-Gadea G, Arenas J, Andreu AL. Molecular genetics of McArdle's disease. Curr Neurol Neurosci Rep. 2007 Jan;7(1):84-92. doi: 10.1007/s11910-007-0026-2. Citation on PubMed
  • Nogales-Gadea G, Rubio JC, Fernandez-Cadenas I, Garcia-Consuegra I, Lucia A, Cabello A, Garcia-Arumi E, Arenas J, Andreu AL, Martin MA. Expression of the muscle glycogen phosphorylase gene in patients with McArdle disease: the role of nonsense-mediated mRNA decay. Hum Mutat. 2008 Feb;29(2):277-83. doi: 10.1002/humu.20649. 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.