This was based on a simulation model of type 2 diabetes complications occurring in incident cases of diabetes diagnosed in a hypothetical population aged 20–40 years according to UKPDS data, with an underlying prevalence of monogenic diabetes of 2% (35% with GCK, 65% with HNF1A or HNF4A), assuming 75% of those with HNF1A or HNF4A would be treated effectively with sulphonylurea monotherapy and that all patients with GCK would discontinue therapy. This evidence concerns the gene HNF4A and type 2 diabetes mellitus.