SNCA and Parkinson disease: The earliest stages of LP (before SNpc involvement) have been linked to the prodromal non-motor symptoms of PD, such as olfactory impairment and gastrointestinal dysfunctions [7], since consistent evidence has demonstrated the presence of α-synuclein aggregates in the gut and in the neurons of the olfactory bulb during the prodromal phase, before the clinical diagnosis of PD [6,8].