GPNMB and Parkinson disease: Alternatively, the increase of KTN1 mRNA expression in the putamen and SNc in PD patients may reflect the consequences of long-term treatments with L-DOPA, or processes in relation to elevated α-synuclein, glycoprotein GPNMB, SN free water, iron accumulation, as has been observed in PD (Barbosa et al., 2015; An et al., 2018; Guttuso et al., 2018; Longhena et al., 2018; Moloney et al., 2018).