We herein presented a case of a ７９-year-old woman who was referred to our hospital with dry mouth and polyuria that had persisted for three months prior to her admission. She developed Hashimoto disease at ７３ years old and pernicious anemia at ７８ years old. Her blood glucose level was ６８２ mg/dl, HbA１c １４．６％, and urinary ketone was positive ; therefore, she was diagnosed with diabetic ketosis. Acute-onset autoimmune type １ diabetes mellitus was diagnosed based on the diagnostic criteria for acute-onset type １ diabetes mellitus （２０１２） by the committee of the Japan Diabetes Society. Autoimmune polyglandular syndrome was subsequently diagnosed based on the complications of type １ diabetes and Hashimoto’s thyroiditis. Her ８７-year-old brother had developed acute-onset autoimmune type １ diabetes ２ months before his sister was hospitalized. Autoimmune polyglandular syndrome type III was also diagnosed because he had autoimmune thyroid disease. No epidemiological data are currently available for late elderly with acute-onset type １ diabetes in Japan. To the best of our knowledge, this is the first case of acute-onset autoimmune type １ diabetes mellitus that developed around the same time period in an elderly brother and sister who were diagnosed with autoimmune polyglandular syndrome type III. Common genetic and environmental factors were etiologically implicated in the almost simultaneous onset between these siblings.
