APP and multiple system atrophy: Besides, several proteins including calbindin D, amyloid precursor protein (APP), S100B, and synuclein-alpha (α-synuclein) have been ascertained in neurodegenerative diseases such as AD, Huntington’s disease (HD), multiple sclerosis, and MSA (Steiner et al., 2011; Stefanits et al., 2014; van Waalwijk van Doorn et al., 2016; Mavroudis et al., 2020).