SNCA and Abnormal autonomic nervous system physiology: More objective assessments, such as polysomnography for RBD or Metaiodobenzylguanidine (MIBG) scintigraphy of the heart for autonomic dysfunction, as well as α-synuclein seeding assay to verify α-synuclein status, could have provided deeper insights into PD phenotypes features, but access to these tests in clinical settings is often challenging.