In contrast, heterozygous inactivating GCK mutations are less deleterious and manifest in a mild fasting hyperglycemia from birth (5.5–8 mmol l−1) otherwise known as maturity-onset diabetes of the young; subtype GCK (GCK-MODY; OMIM entry #125851) (8). This evidence concerns the gene GCK and type 2 diabetes mellitus.