Recently, several neuropeptides such as ghrelin, neuropeptide Y (NPY), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P (SP), and neurotensin have been shown to play neuroprotective roles in PD both in vivo and in vitro (Wang et al., 2015b; Bayliss et al., 2016a; Maasz et al., 2017; Shi et al., 2017; Lazarova et al., 2018; Li et al., 2019). The gene discussed is TFF2; the disease is Parkinson disease.