EGF and Parkinson disease: Also, levels of epidermal growth factor (EGF) and its receptor (EGFR) are decreased in the PD Str and the prefrontal cortex of PD patients, and EGFR+‐NSC numbers are decreased in the SVZ of PD patients (O'Keeffe, Barker, et al., 2009; O'Keeffe, Tyers, et al., 2009b).