Recurrent Myalgia, Dark Urine, and Exercise Intolerance: Glycogen Storage Disease Type X Diagnosed Through Gene Sequencing Panel

Evaluation of a single episode of exercise-induced myalgia, dark urine, and elevated creatine phosphokinase (CPK) levels relies primarily on clinical history and physical examinations. However, recurrent episodes necessitate further investigations for potential genetic conditions. This is a case of an 11-year-old male who presents with recurrent myalgia, dark discolored urine, and exercise intolerance for the past year. The initial examination revealed hematuria and a mild elevation of transaminases. Referral to nephrology showed elevated CPK level, prompting further evaluation by neurology. A DNA sequencing-based neuromuscular genetic panel identified a heterozygous pathogenic variant and two variants of uncertain significance in his genes, leading to a diagnosis of glycogen storage disease X. Metabolic myopathies should be considered in children with recurrent exercise-induced myalgia and dark discoloration of urine. Screening for myoglobinuria, elevated plasma CPK levels, and characteristic acylcarnitine profiles should be considered when clinically indicated. DNA sequencing-based gene panel testing can serve as a non-invasive alternative to muscle biopsy for diagnosing metabolic myopathies when suspicion is high.