Concentrations of CSF YKL-40 were positively associated with α-synuclein in non-demented controls (Spearman’s rho = 0.4824, p = 0.0009), AD (Spearman’s rho = 0.4166, p = 0.0032), DLB (Spearman’s rho = 0.4934, p = 0.0041) and PD patients (Spearman’s rho = 0.4474, p = 0.0003) (for distribution see S2D Fig). This evidence concerns the gene CHI3L1 and Parkinson disease.