​Currently sulphonylureas are the drug of choice when treating patients with HNF1A-diabetes (also known as MODY3). However, no study have investigated combination treatment. This study will provide insight into if combination of incretin based treatment and sulphonylurea may be a good treatment option in patients with HNF1A-diabetes. This study is a glucose-clamp study, where patients will receive combinations of GLP-1, GIP and glimepiride. The effects on insulin and glucagon will be investigated.