SNCA and early-onset autosomal dominant Alzheimer disease: Two of the most common forms of age-related neurodegenerative disorders, Alzheimer’s disease (AD) and Parkinson’s disease (PD), which canonically exhibit accumulations of amyloid β (Aβ) and α-synuclein (αSyn) respectively, often exhibit co-pathology of these proteins and represent keystone components on the spectrum of neurodegenerative disorders [4–18].