HTT and amyotrophic lateral sclerosis: These include tau in tauopathies, α-synuclein in synucleinopathies, such as Parkinson’s disease (PD), TDP-43 in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), huntingtin in Hungtinton’s disease (HD) and amyloid beta (Aβ) in Alzheimer’s disease (AD) (Ross and Poirier, 2004).