Secondary diabetes mellitus: late complication of glycogen storage disease type 1b.

We report a 22 year-old male with glycogen storage disease type 1 (GSD-1) who developed diabetes mellitus secondary to pancreatic islet beta-cell insufficiency. Diabetes mellitus should be considered among the late complications of GSD-1. The pathogenesis of the conversion, from a disease characterized by hypoglycemia to a disease dominated by hyperglycemia, is discussed.