A 3-month-old infant without significant past history was brought to the emergency center by her mother with a generalized tonic-clonic seizure. She is found to have glucose of 5 mg/dL. After correction of her hypoglycemia, she is admitted to your service for further evaluation. Several hours later, her nurse calls to tell you that her bedside glucose check was now 10 mg/dL. You order laboratory work suggested by the pediatric endocrinology team and again correct the infant's hypoglycemia. The results of the laboratory tests you drew include an elevated serum insulin level of 50 μU/mL, and a low IGFBP-1 (plasma insulin-like growth factor binding protein-1). C-peptide levels are not detectable. Which of the following is the likely cause of this child's recurrent hypoglycemia?
a) Congenital adrenal hyperplasia
b) Insulinoma
c) Glycogen storage disease type I
d) Galactosemia