Mitochondrial DNA 3243 mutation may be associated with positivity of zinc transporter 8 autoantibody in cases of slowly progressive type 1 diabetes mellitus.

Slowly progressive type 1 diabetes mellitus (SPIDDM), solely positive for zinc transporter 8 autoantibody (ZnT8A) is rare, and the factors involved in the single positivity remain largely unknown. Thus, this case report aimed to infer the factors based on a literature review. A 40-year-old female was hospitalized for hyperglycemia. She was diagnosed with sensorineural hearing loss and steroid-induced diabetes at 29 and 30 years of age, respectively. She started insulin therapy at 36 years of age, following oral hypoglycemic medication. Blood test results at admission showed fasting serum C-peptide level of 0.29 ng/mL; single positivity for ZnT8A; mitochondrial DNA 3243 mutation; and human leukocyte antigen-DRB1*09:01-DQB1*03:03 associated with Japanese type 1 diabetes. She was diagnosed with ZnT8A-single-positive SPIDDM accompanying mitochondrial diabetes. Most islet cell antibody (ICA)-positive SPIDDM cases with mitochondrial DNA 3243 mutations are negative for glutamic acid decarboxylase autoantibodies, suggesting ZnT8A-single-positive SPIDDM cases among such cases. Therefore, mitochondrial DNA 3243 mutation may be associated with ZnT8A single positivity in SPIDDM.