Is the "preamyloid" of diffuse plaques in Alzheimer's disease really nonfibrillar?

Several papers have described an 'amorphous' component of the amyloid in diffuse plaques and it has been suggested that this is 'preamyloid,' which is not organized into fibrils. Because most of the studies have been performed on autopsy tissue it was the purpose of this study to compare the ultrastructure of diffuse amyloid deposits in well preserved Alzheimer's disease biopsy specimens with autopsy tissues from patients with Alzheimer's disease and Down's syndrome. A postembedding immunogold technique with anti-beta/A4 protein demonstrated gold particles exclusively on extracellular amyloid fibrils in both biopsy and autopsy brains. We have presented evidence that suggests the claim for the existence of an amorphous component within the beta/A4 protein-positive material is unconvincing.