GCK and MODY: To validate our metabolomic profiling results, we collected new serum samples from the following groups of patients: HNF1B-mutated patients, HNF1A-mutated patients, GCK-mutated patients (as the third type of MODY phenotypes), HNF1B-negative patients (patients referred for HNF1B genetic testing due to HNF1B-MODY phenotype but with negative results confirmed by Whole-Genome-Sequencing) and control healthy individuals.