BACKGROUND: Patients with type 1 diabetes mellitus, myasthenia gravis (MG), and Hashimoto disease are diagnosed as having autoimmune polyendocrine syndrome type 3 (APS3). APS3 is rare, and its pathogenesis is unclear. We describe a female patient with APS3 whose human leukocyte antigen (HLA) type could provide a clue to the pathogenesis of APS3.

CASE REPORT: A 40-year-old Japanese female patient who had been diagnosed with MG at 5 years of age, and which had been treated with cholinesterase inhibitors, was referred to our hospital with thirst, polydipsia, polyuria, weight loss, and hyperglycemia. She was found to have type 1 diabetes mellitus based on laboratory tests. She was also positive for anti-thyroid peroxidase antibody and was thus diagnosed with Hashimoto disease. This combination of type 1 diabetes mellitus, myasthenia gravis, and Hashimoto disease led to a diagnosis of APS3. Her HLA serotype was A24; B46/54; DR4/9; DQ8/9, and genotype was A*24: 02; B*46: 01: 01/54: 01: 01; C*01: 02; DRB1*04: 06/09: 01: 02; DQB1*03: 02: 01/03: 03: 02; and DQA1*03: 01/03: 02: 01. We subsequently reviewed 10 cases of APS3 combined with MG, including the present case and cases reported in Japanese. This review revealed that HLA-DR9/DQ9 might be a specific HLA subtype associated with APS3 with MG. Four of the 10 cases had MG diagnosed before diabetes mellitus and autoimmune thyroid disease.

CONCLUSIONS: The present case showed that, in people with HLA-B46 and -DR9, antibody-negative MG can precede the development of APS3 by many years. Physicians should consider the possibility of APS3 when evaluating patients with ocular-type myasthenia gravis, and screen them for type 1 diabetes.

Keywords: Autoimmune Diseases, Diabetes Mellitus, Hashimoto disease, HLA Antigens, Myasthenia Gravis, Polyendocrinopathies, Autoimmune, Diabetes Mellitus, Type 1