APLN and migraine disorder: Neuropeptides directly associated with pain or migraine from significantly differentially expressed neuropeptide prohormone genes include apelin (APLN) [67,68], cortistatin (CORT) [69], IGF2 [70,71], neuromedin B (NMB) [72], neuropeptide W (NPW) [73], PDGFA and platelet-derived growth factor, D polypeptide (PDGFD) [74], TAC4 [75], and VIP [76].