A Case of Type 1 Glycogen Storage Disease with Increased Serum and Urinary C-Peptide Levels

A 30-year-old woman was admitted for evaluation of hepatic function. Hepatomegaly in this patient was originally pointed out when she was one year old. On admission, her liver was palpable 5 f. b. below the costal margin in the right midclavicular line. She was diagnosed as having glycogen storage disease type 1 on the basis of changes in serum lactate levels in response to glucose ingestion and glucagon administration. Her fasting plasma glucose level was 66 mg/d? and her HbA₁C level was 4.0%. The concentration of serum insulin increased slightly from 4.6 U/m? to 19.8 U/m? in response to an injection of 75 g glucose, whereas the concentration of serum C-peptide increased markedly from 1.0 ng/m? to 8.4 ng/m?. In addition, urinary excretion ot C-peptide was remarkably elevated varying from 253 g/day to 268 g/day. As to glucagon secretion, no response of plasma glucagon to hypoglycemia induced by insulin administration was observed, whereas the response of glucagon to arginine administration was normal. This patient is thought to be a rare case of glycogen storage disease type 1 with high levels of serum and urinary C-peptide and with an insensitivity of glucagon secretion to hypoglycemia.