SNCA and Alzheimer disease: Four studies have reported increased CSF oligomeric α-synuclein levels in PD compared with controls (Tokuda et al., 2010; Park et al., 2011; Parnetti et al., 2014a,b), and one of them showed increased CSF α-Syn in PD patients compared with patients with PSP and AD (Tokuda et al., 2010).