Amyloid-forming proteins are implicated in over 30 human diseases. The proteins involved in each disease have unrelated sequences and dissimilar native structures, but they all undergo conformational alterations to form fibrillar polymers. The fibrillar assemblies accumulate progressively into disease-specific lesions in vivo. Substantial evidence suggests these lesions are the end state of aberrant protein folding whereas the actual disease-causing culprits likely are soluble, non-fibrillar assemblies preceding the aggregates. The non-fibrillar protein assemblies range from small, low-order...