Diabetes mellitus secondary to glycogen storage disease type III

SUMMARY Background  Diabetes mellitus is a rare complication of glycogen storage disease type III (GSD III).Case report  We describe a 47‐year‐old man with GSD III who developed diabetes mellitus. He was diagnosed as having GSD III at the age of 18 years, and his glucose tolerance was normal at that time. Liver dysfunction and muscle atrophy gradually progressed, and the patient developed diabetes mellitus at the age of 45. When the post‐prandial hyperglycaemia worsened, we instituted treatment with an alpha‐glucosidase inhibitor, voglibose, and this improved glycaemic control without any adverse effects.Conclusions  We recommend serial evaluation for complications of GSD III, and propose that an alpha‐glucosidase inhibitor may be a favourable drug in treating diabetes mellitus secondary to GSD III.