The varying levels of evidence combined with an expert opinion have led to recommendations for optimum treatment in international guidelines such as the International Society for Pediatric and Adolescent Diabetes (ISPAD)4, with the strongest support for sulfonylureas (SU) as first-line therapy for HNF1A-diabetes and Hepatic Nuclear Factor 4 alpha (HNF4A)-diabetes, no pharmacologic therapy for GCK-related hyperglycemia, insulin for Hepatic Nuclear Factor 1 beta (HNF1B)-diabetes and mitochondrial diabetes (MD) and high-dose SU for KATP-ND. This evidence concerns the gene GCK and diabetes mellitus.