Glucokinase variant-induced maturity-onset diabetes of the young (GCK-MODY) exhibits the unique clinical features of mild fasting hyperglycemia. However, formal studies of its glucose excursion pattern in daily life in comparison with those with or without other types of diabetes are lacking. We conducted a case-control study including 25 patients with GCK-MODY, 25 A1C-matched, drug-naive patients with type 2 diabetes (T2DM), and 25 age-, BMI-, and sex-matched subjects with normal glucose tolerance (NGT). All the subjects wore flash glucose monitoring (FGM) sensors for 2 weeks, and glucose readings were masked. Glucose excursion was significantly lower in the GCK-MODY than that in A1C-matched T2DM during the daytime, but was similar during the nighttime. The daytime coefficient of variation (CV) driven by postprandial glucose could separate GCK-MODY from well-controlled T2DM, but the nighttime CV could not. In discriminating between GCK-MODY and T2DM, the area under the curve of the CV was 0.875. However, in GCK-MODY and NGT subjects, the CVs were similar at 24 h, whereas the other four excursion parameters were significantly higher in GCK-MODY than those in NGT subjects. FGM confirmed the stability and mildness of hyperglycemia in GCK-MODY patients. Postprandial regulation is a key driver of the difference in excursion between GCK-MODY and T2DM.

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