Pituitary adenylate cyclase-activating peptide-38 (PACAP38) and vasoactive intestinal peptide (VIP) are both members of the vip glucagon, growth hormone-releasing factor-secretin superfamily, and their possible involvement in the initiation of attacks is supported by elevated plasma levels of PACAP and VIP during spontaneous CH attacks. The gene discussed is ADCYAP1; the disease is cyclic hematopoiesis.