SNCA and Alzheimer disease: Parkinson’s disease (PD) is the second most common age-related neurodegenerative disease after Alzheimer's disease (AD), characterized by the loss of dopaminergic neurons located in the substantia nigra pars compacta and the presence of protein inclusions called Lewy bodies or Lewy neurites, which are composed of mainly α-synuclein (α-syn), a presynaptic protein [1].