Molecular genetic findings of the recent 10–15 years contributed to the understanding of different subtypes of diabetes mellitus caused by a single gene defect. APECED and IPEX syndrome represent rare monogenic forms of autoimmune diabetes mellitus. Single gene inborn defects of beta-cell function include a prevalent glucokinase defect (MODY2), a rare failure of potassium channel subunit Kir6.2 associated with permanent neonatal diabetes mellitus, and relatively abundant defects of components of transcriptional regulation network of beta-cells (“transcriptional factor diabetes” – MODY1, 3, 4, 5 and 6). Also cystic fibrosis related diabetes, DIDMOAD or Wolfram syndrome and diabetes mellitus caused by a mitochondrial DNA defect may be regarded as single gene diabetes in the broader sense. For some patients, an exact diagnostic evaluation may bring novel and more attractive therapeutic options. Additionally, every newly diagnosed patients contributes to the general understanding of the function of beta-cell, that is functionally one of the most sophisticated cells of the human body.

        Key words: diabetes mellitus, APECED, IPEX syndrome, glucokinase, Kir6.2, MODY