PHKA1 encodes the alpha regulatory subunit of phosphorylase kinase (PhK), a key enzyme complex that regulates glycogen breakdown in muscle tissue through phosphorylation of glycogen phosphorylase 1. The protein functions as part of a multimeric PhK complex responsible for controlling glycogen catabolism, particularly in skeletal muscle 2. PHKA1 is located on the X chromosome X follows X-linked inheritance patterns 3. Mutations in PHKA1 cause glycogen storage disease type IXd (GSD IXd), which presents with variable clinical manifestations including exercise intolerance, myalgia, muscle cramps, myoglobinuria, and progressive muscle weakness 2. Some patients develop late-onset distal myopathy affecting calf muscles without exercise intolerance 4. Emerging evidence suggests PHKA1 may have broader roles beyond muscle metabolism, with recent studies indicating potential involvement in cognitive impairment and brain development 2, as well as oncogenic functions in breast and lung cancers where elevated expression correlates with poor prognosis and enhanced glycolytic activity 56. The rarity of PHKA1-related disorders and limited case reports highlight the need for better recognition and understanding of this gene's diverse biological functions.