The Clinical and Biological Relationship between Type II Diabetes Mellitus and Alzheimer's Disease

The clinical relationship between Type II diabetes mellitus and Alzheimer's disease has been debated for over a decade. While several studies have not shown a clear clinical correlation, others have demonstrated that Type II diabetes is an independent risk factor for Alzheimer's disease. Why diabetes would increase the likelihood of Alzheimer's disease is not immediately clear, although recent studies have demonstrated an impact of insulin abnormalities, insulin resistance and advanced glycation end products on both the development of neural amyloid plaques and neurofibrillary tangles. Although endodermal in embryologic development, the pancreas is a highly innervated organ that shares a number of molecular similarities with brain at the level of the transcriptome and proteome. Type II diabetes and Alzheimer's disease are characterized by localized amyloid deposits that progress during the course of the disease. Comparing amyloid deposition in the brain and pancreas reveals some striking pathophysiologic similarities. Neurodegeneration in pancreatic islets, as manifested by neurofibrillary tangles, is less well studied than in Alzheimer's disease but may also occur. This review summarizes what is currently known about the clinical and biological relationships and similarities between Type II diabetes and Alzheimer's disease.