SNCA and Alzheimer disease: Because the predominant source of α-synuclein in CSF is considered to be the central nervous system [43], the decrease in the level of CSF α-synuclein in DLB may reflect a dysfunction in the metabolism or clearance of α-synuclein in the brain, similarly to AD patients with Aβ accumulation in the brain showing a decrease in the level of Aβ42 in CSF.