GCK-MODY is characterized by non-progressive asymptomatic mild hyperglycemia that is present from birth and may remain in the prediabetes state rather than progress to diabetes.30 As noted, there was 100% penetrance for carriers of clinically significant GCK variants developing diabetes or prediabetes; in addition, all those with glycated hemoglobin (HbA1c) values available (N = 13) had levels consistent with GCK-MODY, ranging from 5.7 to 7.2% (HbA1c in GCK-MODY is typically 5.6–7.6%31) (Supplementary Data 5). This evidence concerns the gene GCK and diabetes mellitus.