Genetic testing is generally not necessary for diabetes, genetic testing is for some special types of diabetes, such as mitochondrial gene mutation diabetes. Genetic testing for specific types of diabetes is necessary to help clarify the diagnosis. Genetic diagnosis can be done for patients suspected of having single gene mutation diabetes. For example, single gene defects in pancreatic islet beta cell function such as glucokinase gene mutation resulting in adult onset diabetes mellitus in adolescents, single gene defects in insulin action such as insulin receptor gene mutation resulting in type A insulin resistance, short goblin look syndrome, and so on. Special types of diabetes caused by genetic defects in pancreatic β-cell function, such as mitochondrial gene mutation diabetes, mitochondrial gene mutation diabetes is the most common single-gene mutation diabetes mellitus, accounting for 0.6% of all adult diabetes mellitus in China. When special type of diabetes mellitus is suspected, genetic testing or chromosome examination can be done according to the clinical characteristics of the patient, in order to clarify the diagnosis and treatment as early as possible, and follow the doctor’s instructions to actively treat the disease.