Recent studies have demonstrated that the GPNMB is selectively up-regulated, and can be a disease-associated biological marker in several neurodegenerative diseases such as NPC1 (Marques et al, 2016; Fukaura et al, 2021; Rodriguez-Gil et al, 2021), Gaucher disease (Zigdon et al, 2015; Kramer et al, 2016), ALS (Tanaka et al, 2012), AD (Hüttenrauch et al, 2018; Aichholzer et al, 2021), and PD (Moloney et al, 2018). Here, NPC1 is linked to Parkinson disease.