Leptin and its receptor, Lepr, have been shown to be involved in leptin-dependent adult hippocampal neurogenesis [57] and mediated neuroprotection of dopaminergic cells via activation of Jak-Stat, mitogen-activated protein kinases (MEK)/extracellular signal-regulated kinases (ERK) and growth factor receptor-bound protein 2 (GRB2) signaling pathways in a mouse model of Parkinson’s disease [58]. The gene discussed is GRB2; the disease is Parkinson disease.