SNCA and Parkinson disease: This result reflects the neuronal loss and α-synuclein degeneration of the brainstem nucleus, so the brain region affected by RBD is in the second phase of the Braak hypothesis (Braak et al., 2003), RBD maybe precede the emergence of other symptoms of PD in the Braak disease flow chart, and it can become suggestive of preclinical PD.