SNCA and Parkinson disease: Further, although there are pathological hallmarks of PD (dopaminergic neuronal dysfunction in the substantia nigra pars compacta and Lewy-body formation from misfolded α-synuclein proteins) (MacMahon Copas et al. 2021; Dickson 2018; Levin et al. 2016), it is difficult to distinguish PD from other Lewy body disease such as Lewy-body dementia (LBD), idiopathic rapid eye movement sleep behaviour disorder, and pure autonomic failure, especially during the early disease stages (Levin et al. 2016; Sezgin et al. 2019).