While many studies have reported a lower mean total α-synuclein in CSF of PD patients with respect to age-matched controls or other neurological controls, a few studies failed to find any significant difference between the PD and control groups (Tokuda et al., 2006; Mollenhauer et al., 2008, 2011, 2013; Ohrfelt et al., 2009; Hong et al., 2010; Park et al., 2011; Parnetti et al., 2011; Shi et al., 2011; Hall et al., 2012; Toledo et al., 2013; van Dijk et al., 2013; Hansson et al., 2014; Wennström et al., 2013). This evidence concerns the gene SNCA and Parkinson disease.