Even though sequence variations within NR4A2 are not considered a widespread genetic cause of PD (Nichols et al., 2004; Tan et al., 2004), one mutation leading to decreased Nurr1 expression has been identified in a PD patient (Sleiman et al., 2009), and decreased Nurr1 expression has also been reported in midbrain dopaminergic neurones from patients with idiopathic PD (Jankovic et al., 2005). This evidence concerns the gene NR4A2 and Parkinson disease.