MAPT and early-onset autosomal dominant Alzheimer disease: Fibril polymorphism has been shown to be responsible for the development of different diseases caused by the same protein [e.g., αSyn causing Parkinson’s disease or Multiple System Atrophy or Dementia with Lewy Bodies (Shahnawaz et al., 2020) or Tau causing Alzheimer’s disease, Pick’s disease, chronic traumatic encephalitis, and corticobasal degeneration (Fitzpatrick et al., 2017; Falcon et al., 2018; Scheres et al., 2020)].