Glucokinase (GK) catalyses the key regulatory step in glucose-stimulated insulin secretion. Correspondingly, hetero- and homozygous mutations in human cause maturity-onset diabetes of the young (GCK-MODY) and permanent neonatal diabetes (PNDM), respectively. To explore the possible utility of glucokinase activators (GKA) and of glucagon-like receptor-1 (GLP-1) agonists in these diseases, we have developed a novel hypomorphic allele in mice encoding an aberrantly spliced mRNA deleted for exons 2 and 3. In islets from homozygous knock-in (Gck) mice, GK immunoreactivity was reduced by >85%, and glucose-stimulated insulin secretion eliminated. Homozygous Gck mice were smaller than wildtype littermates and displayed frank diabetes (fasting blood glucose >18 mmol/L; HbA1c ~12%), ketosis and nephropathy. Heterozygous Gck mice were glucose intolerant (HbA1c ~5.5%). Abnormal glucose-stimulated Ca dynamics and beta cell-beta cell connectivity in Gck islets were completely reversed by the recently-developed GKA, dorzagliatin, which was largely inactive in homozygous Gck mouse islets. The GLP-1 receptor agonist exendin-4 improved glucose tolerance in male Gck mice, an action potentiated by dorzagliatin, in male but not female mice. Sex-dependent additive effects of these agents were also observed on insulin secretion . Combined treatment with GKA and incretin may thus be useful in -MODY or -PNDM.