Glycogen storage disease type X (GSDX) is an autosomal recessive condition that results in a metabolic myopathy which primarily manifests with exercise intolerance, muscle cramps and myoglobinuria. It has been historically found in adults. We present a case of an infant who presented with tongue fasciculations and was found to have GSDX.
To describe an atypical presentation of GSDX.
A 9-month-old African American male presented with tongue fasciculations in the setting of elevated creatine kinase (CK). His developmental milestones were appropriate for age. Physical exam was remarkable for tongue fasciculations. Spinal muscular atrophy was ruled out with molecular testing. Nerve conduction studies and electromyogram were normal though the rest potentials were difficult to obtain due to limited cooperation. A comprehensive neuromuscular panel found 2 pathogenic PGAM2 mutations of the common null variant c.233G>A. On subsequent testing both parents and a sibling were found to be carriers of the same PGAM2 mutation.
What makes our patient unique is that he is the youngest person with GSDX to be reported. We found a rare disorder incidentally with a symptom that was not previously associated. The authors would encourage PGAM2 testing in those with muscle cramping, myoglobinuria or elevated CK without any other etiology. More widespread testing can help us understand the full symptom profile of GSDX. Further, early diagnosis allows for anticipatory guidance on exercise and overexertion to prevent those with GSDX from pushing themselves into rhabdomyolysis. Conclusively, fasciculations may be an independent presenting symptom of GSDX and should be considered if other causes are ruled out.