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GSD9 was first described in 1966. It is categorized into four subtypes - 9a, 9b, 9c and 9d, of which only GSD9d is a muscle GSD. It is also known as muscle phosphorylase kinase deficiency. It is an extremely rare form of the disorder.
Estimated cases diagnosed worldwide: <100.



Muscle pain during and following activity. Possible progressive muscle weakness and atrophy.




Childhood (rare), and adulthood.


Skeletal muscle.


High-protein, complex carbohydrate diet.


Good with avoidance of intense exercise.

IamGSD would welcome hearing from patients, doctors and researchers who could help us to improve and expand our information on this extremely rare Muscle GSD.

Affected individuals may experience pain, muscle cramps or contractures during activity. This can lead to dark-coloured urine (myoglobinuria) due to the release of myoglobin from breakdown of the muscle. Over time they may develop progressive muscle degeneration and weakness.

GSD9d is caused by a mutation in the PHKA1 gene and has X-linked inheritance. It is these days normally diagnosed through genetic testing but sometimes a muscle biopsy is also undertaken. 

There are some case reports of GSD9d summarised on the OMIM website. Many cases are not diagnosed until adulthood.


Very little is know about GSD9d, but given that affected individuals experience “exercise intolerance” (better thought of as “physical activity intolerance”), it would be reasonable to follow the same advice about avoiding rhabdomyolysis as is given for McArdle disease (GSD5). In addition, the same advice applies for when to seek medical attention in the event of a strong cramp or contracture.


It is very likely that with the advent of Next Generation Sequencing and a gene panel for conditions which can be the cause of rhabdomyolysis, more cases of GSD9d will be identified. As understanding of the condition grows, IamGSD will be able to offer better support for this extremely rare muscle GSD.

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We have a Facebook group dedicated to GSD9d and the number of members is slowly building. It can be very helpful to share with others affected by the same condition. For more details and a link go to our page for “Join social media”.


 We will endeavor to let you know here of recent research on GSD9d. 

Frontiers in Neurology, August 2022
Expanding the clinicopathological-genetic spectrum of glycogen storage disease type IXd by a Chinese neuromuscular center.
Go to paper.


We have only heard of a few dozen cases of GSD9d worldwide, and we know it is really difficult for those affected to find each other and swap notes. If you have GSD9d, as well as making use of our Facebook group, please contact us so that we can try to put people in touch with each other.

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