SNCA and Parkinson disease: According to Braak's hypothesis, sporadic PD development can originate from a pathogen entering the body via the nasal cavity or gut and can subsequently migrate to the brain, facilitating Lewy body formation.111 Hyposmia and GI dysfunction are commonly observed as early symptoms of PD and often precede the formal PD diagnosis.99 Aggregation of alpha-synuclein (ASN) and formation of Lewy bodies are the characteristic pathophysiological features of PD.