ENO3 and hyperinsulinemic hypoglycemia, familial, 4: Glycogen storage disease type XIII (GSDXIII) is a very rare inherited metabolic myopathy characterized by an enzymatic defect of the distal part of glycolysis; to date only four patients have been reported in the literature1, 2 The condition is caused by recessive mutations in ENO3 (OMIM # 131370) resulting in muscle β‐enolase deficiency.