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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed July 2010

What is the official name of the PYGM gene?

The official name of this gene is “phosphorylase, glycogen, muscle.”

PYGM is the gene's official symbol. The PYGM gene is also known by other names, listed below.

What is the normal function of the PYGM gene?

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.

How are changes in the PYGM gene related to health conditions?

glycogen storage disease type V - caused by mutations in the PYGM gene

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.

Where is the PYGM gene located?

Cytogenetic Location: 11q12-q13.2

Molecular Location on chromosome 11: base pairs 64,746,389 to 64,760,715

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The PYGM gene is located on the long (q) arm of chromosome 11 between positions 12 and 13.2.

The PYGM gene is located on the long (q) arm of chromosome 11 between positions 12 and 13.2.

More precisely, the PYGM gene is located from base pair 64,746,389 to base pair 64,760,715 on chromosome 11.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about PYGM?

You and your healthcare professional may find the following resources about PYGM helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the PYGM gene or gene products?

  • glycogen phosphorylase, muscle form
  • myophosphorylase

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding PYGM?

breakdown ; enzyme ; gene ; glucose ; glycogen ; muscle cells ; mutation ; phosphate ; simple sugar

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Aquaron R, Bergé-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. Epub 2007 Feb 26. (
  • 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. (
  • Deschauer M, Morgenroth A, Joshi PR, Gläser 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. Epub 2007 Apr 3. (
  • NCBI Gene (
  • Nogales-Gadea G, Arenas J, Andreu AL. Molecular genetics of McArdle's disease. Curr Neurol Neurosci Rep. 2007 Jan;7(1):84-92. Review. (
  • Nogales-Gadea G, Rubio JC, Fernandez-Cadenas I, Garcia-Consuegra I, Lucia A, Cabello A, Garcia-Arumi E, Arenas J, Andreu AL, Martín 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. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: July 2010
Published: February 1, 2016