NR4A2 and Parkinson disease: Numerous studies, such as age-based declines in Nurr1 immunoreactivity in human substance nigra (Chu et al., 2002), Nurr1 in PD and related diseases (Chu et al., 2006), decreased NURR1 gene expression in PD3 patients (Le et al., 2008; Liu et al., 2012), decreased NURR1 and Pituitary homeobox 3 (PITX3) gene expression in PD Chinese patients (Liu et al., 2012), decreased Nurr1 mRNA in peripheral blood lymphocytes in PD patients (Montarolo et al., 2016; Li et al., 2018; Yang et al., 2019), are erudite evidence that PD is related to the NR4A2 (Nurr1) shortfall.