Anecdotal evidence from routine clinical care suggests that patients with sulphonylurea-treated KCNJ11 neonatal diabetes, when they eat, may experience mild hypoglycaemia if the food consumed lacks carbohydrate. It has been suggested that this may be due to regulation of insulin secretion via the incretin pathway as opposed to the classical ATP pathway. Therefore the investigators hypothesise that foods with a relatively high protein content compared to those with a relatively high carbohydrate content will result in excessive insulin secretion and relatively lower glucose values in KCNJ11 patients. This would be in contrast to healthy control subjects or subjects with SU-treated T2D where the insulin secretion will be moderated by the ambient glucose via the classical ATP pathway. The investigators will formally study this hypothesis by comparing the insulin, glucose and incretin hormone responses to a high protein meal with a high carbohydrate meal in people with KCNJ11 neonatal diabetes, people without diabetes and people with sulphonylurea-treated Type 2 Diabetes. To assess whether any effect seen is due to direct stimulation of the beta cell by the sulphonylurea itself, people with KCNJ11 neonatal diabetes will also undergo the same tests in the fasting state, having taken the sulphonylurea in the absence of any food.