CALCA and migraine disorder: Some studies identified the involvement of two endogenous neuropeptides in the pathophysiology of migraine: CGRP and PACAP.34 CGRP manifests in two human isoforms: α-CGRP and β-CGRP, encoded by the CALCA and CALCB genes, respectively.35 On the other hand, PACAP is encoded by the ADCYAP1 gene and exhibits two functional isoforms: PACAP38 (representing approximately 90% of total PACAP) and PACAP27.