Patients with MODY due to a heterozygous inactivating mutation in the GCK gene are frequently misdiagnosed with type 1 (T1D) or type 2 (T2D) diabetes yet they have lifelong mild fasting hyperglycaemia[3], [4], [5], [6], pharmacological treatment is rarely required [5], [7], [8] and the development of complications is atypical [8], [9], [10], [11], [12], [13]. Here, GCK is linked to diabetes mellitus.