HNF1A and maturity-onset diabetes of the young type 3: After in vivo maturation, the WT β-like cells secreted insulin (≥2-fold insulin fold change) and C-peptide (≥1.5-fold C-peptide fold change) in response to high glucose, while the mutant HNF1A+/H126D β-like cells were non-responsive (Figs. 6c and S8a), consistent with the pathophysiology of our MODY3 patients.