Rapid progression of β-cell dysfunction in a patient with glycogen storage disease type 1a complicated by diabetes: longitudinal assessment by serial OGTTs with a review of the literature.

Glycogen storage disease type 1a (GSD1a) is characterized by hypoglycemia in childhood; however, cases complicated by diabetes in adulthood have increasingly been reported. The clinical phenotype of GSD1a appears heterogeneous, and insulin secretory capacity in the patients has not been fully characterized. Herein, we report the case of a 20-year-old woman with GSD1a who was initially diagnosed with type 2 diabetes in early adulthood. The patient's glycemic control gradually deteriorated despite administration of oral antidiabetic agents. Longitudinal evaluation using 75-g oral glucose tolerance tests demonstrated a marked decline in insulin secretion within 10 months. Based on these findings, insulin therapy was initiated, resulting in stable glycemic control. This case suggests that rapid β-cell decompensation occurs during the clinical course of early-onset diabetes in young patients with GSD1a.