GRN and Parkinson disease: Indeed, reduced levels of PGRN have been linked to AD (Kelley et al., 2010; Lee et al., 2011; Minami et al., 2014; Sheng et al., 2014; Redaelli et al., 2017) and Parkinson’s disease (Chang et al., 2013; Mateo et al., 2013; Van Kampen et al., 2014; Chen et al., 2015).