NR4A2 and Parkinson disease: The Nurr1 level in mDA neurons decreases in the elderly (Chu et al, 2002) and PD patients (Bauer et al, 2008), and polymorphisms and mutations resulting in reduced expression of Nurr1 are associated with familial and sporadic PD (Le et al, 2003; Zheng et al, 2003; Hering et al, 2004).