National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Muscular phosphorylase kinase deficiency

The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.
orphanet

Orpha Number: 715

Definition
Glycogen storage disease due to muscle phosphorylase kinase (PhK) deficiency is a benign inborn error of glycogen metabolism characterized by exercise intolerance.

Epidemiology
The disease is very rare with less than 30 patients reported in the literature.

Clinical description
The disease starts generally in adolescence or adulthood. Patients may present with exercise intolerance with myalgia, cramps, fatigue, and sometimes myoglobinuria. In some cases, patients may present with progressive muscle weakness. Symptoms are usually mild, and myopathy may be asymptomatic. A neonatal form with generalized muscular hypotonia and respiratory insufficiency has also been described.

Etiology
Phosphorylase kinase (PhK) is an enzyme which plays a key role in the regulation of glycogenolysis as it is required for glycogen phosphorylase activation. It consists of four copies of each four subunits (alpha, beta, gamma and calmoduline) encoded by different genes on different chromosomes and differentially expressed in various tissues. Muscle-specific isoforms of the alpha and gamma subunits are encoded by the PHKA1 gene and the PHKG1 gene respectively, but until now mutations have been only identified in the PHKA1 gene and the transmission is X-linked.

Diagnostic methods
Biochemical diagnosis of the muscle form can be made by measuring phosphorylase kinase activity in a muscle biopsy. Genetic testing is useful to confirm or establish the diagnosis.

Differential diagnosis
Differential diagnoses include GSD due to myophosphorylase deficiency (GSD type V), and other GSDs affecting the muscle (GSD types XI, XII, XIII and XIV) (see these terms).

Management and treatment
Most patients do not require any specific treatment.

Prognosis
Prognosis is generally good.

Visit the Orphanet disease page for more resources.
Last updated: 5/1/2011

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In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.

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