Most studies, systematic reviews, and meta-analyses which examined the validity of α-synuclein in the CSF as a putative biomarker for PD emphasized that a decreased level of α-synuclein in CSF reliably separated PD from control subjects, but the specificity of this measurement was low (Mollenhauer et al., 2011, 2013; Aerts et al., 2012; Gao et al., 2015; Zhou et al., 2015; Chahine et al., 2020). This evidence concerns the gene SNCA and Parkinson disease.