Case reportPGM1 deficiency: Substrate use during exercise and effect of treatment with galactose

•PGM1 deficiency is associated with severe exercise intolerance due to a block in skeletal muscle glycogenolytic capacity.•Oral galactose treatment in adults with PGM1 deficiency is safe and improves walking distance.•Galactose treatment tends to normalize skeletal muscle substrate use from fat to carbohydrates during exercise.

Mutations in PGM1 (phosphoglucomutase 1) cause Glycogen Storage Disease type XIV, which is also a congenital disorder of protein N-glycosylation. It presents throughout life as myopathy with additional systemic symptoms. We report the effect of oral galactose treatment during five months in a patient with biochemically and genetically confirmed PGM1 deficiency. The 12-minute-walking distance increased by 225 m (65%) and transferrin glycosylation was restored to near-normal levels. The exercise assessments showed a severe exercise intolerance due to a block in skeletal muscle glycogenolytic capacity and that galactose treatment tended to normalize skeletal muscle substrate use from fat to carbohydrates during exercise.