Abstract
Diabetes has historically been thought of as a medical specialty which primarily deals with treatment rather than diagnosis. Molecular genetic testing can now be used to make a diagnosis of the 1-2% of all diabetic patients with monogenic diabetes. Making a diagnosis of monogenic diabetes is important as it can have a dramatic effect on the treatment a patient should receive: glucokinase MODY patients need no treatment; HNF1alpha MODY patients are very sensitive to low dose sulphonylureas; and patients with neonatal diabetes due to Kir6.2 mutations, despite being insulin dependent, can discontinue insulin and be well controlled on high dose sulphonylurea tablets. The challenge for diabetologists is to use clinical skills to detect these monogenic patients whose care will be greatly helped by the treatment changes that follow molecular genetic testing.