INS and hyperinsulinism: Compared to 2.5-month wild-type littermates, the Csn2WT/K70E mice have normal levels of fed blood glucose, free fatty acid, and triglyceride (Fig. 1b and Fig. S1b, c), but display fasting hypoglycemia (Fig. 1b), hyperinsulinemia (Fig. 1c), and elevated levels of the degradation-resistant proinsulin cleavage product: C-peptide (Fig. 1d), indicating enhanced insulin secretion.