Maximal Multistage Shuttle Run Test-induced Myalgia in a Patient with Muscle Phosphorylase B Kinase Deficiency

Area of Science:

• Biochemistry
• Genetics
• Metabolic Disorders

Background:

• Muscle phosphorylase b kinase (PHK) deficiency is a rare metabolic disorder.
• It is caused by mutations in the PHKA1 gene, which encodes the alpha-M subunit of PHK.
• This enzyme plays a crucial role in glycogen metabolism within muscle tissue.

Observation:

• A 16-year-old male experienced myalgia during maximal exercise testing.
• An ischemic forearm exercise test was normal, but a muscle biopsy showed subsarcolemmal glycogen accumulation.
• This indicated a potential issue with glycogen breakdown or utilization.

Findings:

• A novel insertion mutation in the PHKA1 gene was identified in the patient.
• This mutation led to premature termination of the alpha-M subunit of PHK.
• The patient exhibited a relatively mild reduction in PHK activity compared to previously reported cases.

Implications:

• This case expands the known spectrum of PHKA1 mutations associated with PHK deficiency.
• It highlights the importance of genetic testing and muscle biopsy in diagnosing unexplained myalgia during exercise.
• Understanding novel mutations can improve diagnosis and management of this rare metabolic disorder.