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

Muscle phosphorylase b kinase (PHK) deficiency is a rare mild metabolic disorder caused by mutations of the PHKA1 gene encoding the alpha M subunit of PHK. A 16-year-old boy experienced myalgia during the maximal multistage 20-m shuttle run test targeting the maximal oxygen consumption. Although an ischemic forearm exercise test was normal, a muscle biopsy revealed subsarcolemmal glycogen accumulation. He harbored a novel insertion mutation in the PHKA1 gene that resulted in premature termination of the aM subunit close to the C-terminus. Compared with previously reported cases, his reduction in PHK activity was relatively mild.