Ultrastructure of amyloid fibrils in Alzheimer's disease and Down's syndrome.

Amyloid fibrils in brains of patients with Alzheimer's disease and Down's syndrome were examined by light and electron microscopy. In addition, replicas of amyloid fibrils produced by a quick freezing method from the brain of a patient with Down's syndrome were examined by electron microscopy. The amyloid fibrils were shown to consist of hollow rods. These were composed of filaments arranged as a tightly coiled helix, each turn of which consisted of five globular subunits. This structure appears to be similar to the prion filament observed in Creutzfeldt-Jakob disease (CJD). The possibility therefore arises that amyloid fibrils in Alzheimer's disease and Down's syndrome may be related to the transmissible agents responsible for diseases such as CJD, kuru and Gerstmann-Sträussler Syndrome (GSS).