An autopsy case of Down's syndrome complicated with autoimmune diabetes mellitus and chronic thyroiditis

We report findings for an autopsy case of a 38-year-old woman with Down's syndrome complicated by type 1 diabetes and Hashimoto's thyroiditis. Although the patient was first diagnosed with NIDDM based on her insulin secretion at age 16, her fasting C-peptide gradually decreased, necessitating insulin treatment at 20 years of age. Anti-GAD antibody, HLA DR 9 (DRB 1*0901) and thyroid antibodies were positive at 35 years of age. Due to diabetic complications progressing over the 20 years, she died of renal failure at age 38. Mitochondrial DNA 3357 (G-A) mutation and β₃-adrenergic receptor gene polymorphism were also demonstrated in this case. A pathological examination showed the following: 1) histological findings for the thyroid were compatible with Hashimoto's thyroiditis. 2) The number of islets decreased markedly in the pancreatic tail with hardly any detectable β cells and, while α cells were relatively well preserved. These findings suggest that autoimmunity in addition to gene mutations may have caused her diabetes. An increased prevalence of type 1 diabetes in Down's syndrome is well established, but, its mechanism remains to be clarified. Future genetic studies are thus required to clarify the cause of type 1 diabetes associated with Down's syndrome.