Here we aimed to evaluate the disease-specificity of increased YKL-40 levels in cerebrospinal fluid (CSF) from AD patients with mild to moderate dementia (n = 49) versus Parkinson’s disease (PD) (n = 61) and dementia with Lewy bodies (DLB) patients (n = 36), and non-demented controls (n = 44). The gene discussed is CHI3L1; the disease is Parkinson disease.