HTT and neurodegenerative disease: Poirier et al. examined the aggregation of huntingtin fragment, and found that intermediate species such as oligomers and protofibrils are produced before amyloid formation of the polyQ proteins, which are structurally similar to those of amyloid-β and α-synuclein formed in Alzheimer’s disease and Parkinson’s disease, implying the pathogenic mechanism shared among the neurodegenerative diseases associated with protein aggregation [53].