CHI3L1 and Parkinson disease: The study aimed to validate the reference interval (RI) for serum chitinase 3‐like 1 (S CHI3L1) in a control group and measure the CHI3L1 concentration in different diagnostic groups, including individuals with AD, non‐AD dementia, Parkinson's disease, other movement disorders, a combination of a cognitive syndrome and a movement disorder, and healthy controls.