With respect to YKL-40 and PD, results from CSF studies are conflicting; some studies found the same concentration in PD patients as in controls (Magdalinou et al., 2015; Wennström et al., 2015; Hall et al., 2016), whereas others found YKL-40 to be lower in PD patients compared to controls (Olsson et al., 2013; Hall et al., 2018). The gene discussed is CHI3L1; the disease is Parkinson disease.