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


Reviewed August 2015

What is the official name of the PHKA1 gene?

The official name of this gene is “phosphorylase kinase, alpha 1 (muscle).”

PHKA1 is the gene's official symbol. The PHKA1 gene is also known by other names, listed below.

What is the normal function of the PHKA1 gene?

The PHKA1 gene provides instructions for making one piece, the alpha subunit, of the phosphorylase b kinase enzyme. This enzyme is made up of 16 subunits, four each of the alpha, beta, gamma, and delta subunits. (Each subunit is produced from a different gene.) The alpha subunit helps regulate the activity of phosphorylase b kinase. This enzyme is found in various tissues, although it is most abundant in the liver and muscles. One version of the enzyme is found in liver cells and another in muscle cells. The alpha-1 subunit produced from the PHKA1 gene is part of the enzyme found in muscle cells.

Phosphorylase b kinase plays an important role in providing energy for cells. The main source of cellular energy is a simple sugar called glucose. Glucose is stored in muscle and liver cells in a form called glycogen. Glycogen can be broken down rapidly when glucose is needed, for instance during exercise. Phosphorylase b kinase turns on (activates) another enzyme called glycogen phosphorylase b by converting it to the more active form, glycogen phosphorylase a. When active, this enzyme breaks down glycogen.

How are changes in the PHKA1 gene related to health conditions?

glycogen storage disease type IX - caused by mutations in the PHKA1 gene

At least seven mutations in the PHKA1 gene are known to cause a form of glycogen storage disease type IX (GSD IX) called GSD IXd or X-linked muscle glycogenosis. This form of the disorder is rare and not well understood. It affects muscles and can cause muscle weakness, pain, and cramping, particularly during exercise, although some affected individuals have no signs or symptoms of the condition. Mutations in the PHKA1 gene reduce the activity of phosphorylase b kinase in muscle cells, although the mechanism is unknown. Reduction of this enzyme's function impairs glycogen breakdown. As a result, glycogen builds up in cells, and glucose is not available for energy. Reduced energy production in muscle cells leads to the features of GSD IXd.

Where is the PHKA1 gene located?

Cytogenetic Location: Xq12-q13

Molecular Location on the X chromosome: base pairs 72,578,814 to 72,714,181

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

The PHKA1 gene is located on the long (q) arm of the X chromosome between positions 12 and 13.

The PHKA1 gene is located on the long (q) arm of the X chromosome between positions 12 and 13.

More precisely, the PHKA1 gene is located from base pair 72,578,814 to base pair 72,714,181 on the X chromosome.

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

Where can I find additional information about PHKA1?

You and your healthcare professional may find the following resources about PHKA1 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 PHKA1 gene or gene products?

  • PHKA
  • phosphorylase b kinase regulatory subunit alpha, skeletal muscle isoform
  • phosphorylase kinase, alpha 1 (muscle), muscle glycogenosis
  • phosphorylase kinase alpha M subunit

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

What glossary definitions help with understanding PHKA1?

breakdown ; enzyme ; gene ; glucose ; glycogen ; kinase ; muscle cells ; simple sugar ; skeletal muscle ; subunit

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


  • Brushia RJ, Walsh DA. Phosphorylase kinase: the complexity of its regulation is reflected in the complexity of its structure. Front Biosci. 1999 Sep 15;4:D618-41. Review. (
  • NCBI Gene (
  • Preisler N, Orngreen MC, Echaniz-Laguna A, Laforet P, Lonsdorfer-Wolf E, Doutreleau S, Geny B, Akman HO, Dimauro S, Vissing J. Muscle phosphorylase kinase deficiency: a neutral metabolic variant or a disease? Neurology. 2012 Jan 24;78(4):265-8. doi: 10.1212/WNL.0b013e31824365f9. Epub 2012 Jan 11. (
  • Wuyts W, Reyniers E, Ceuterick C, Storm K, de Barsy T, Martin JJ. Myopathy and phosphorylase kinase deficiency caused by a mutation in the PHKA1 gene. Am J Med Genet A. 2005 Feb 15;133A(1):82-4. (
  • Ørngreen MC, Schelhaas HJ, Jeppesen TD, Akman HO, Wevers RA, Andersen ST, ter Laak HJ, van Diggelen OP, DiMauro S, Vissing J. Is muscle glycogenolysis impaired in X-linked phosphorylase b kinase deficiency? Neurology. 2008 May 13;70(20):1876-82. doi: 10.1212/01.wnl.0000289190.66955.67. Epub 2008 Apr 9. (


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: August 2015
Published: February 8, 2016