Is Alzheimer's a homogeneous disease,Are plaques critical and Does the blood brain barrier really contribute?

Several problems exist with the speculative hypothesis presented. The relationship between neuritic plaques and clinical symptoms is not well established and is further complicated by the likely existence of multiple subforms of Alzheimer's disease. Moreover, direct support for changes in the blood brain barrier with Alzheimer's disease is lacking, and the available circumstantial evidence argues against it having an important role in the pathogenesis of the disease.