In addition, one of two PACAP forms (PACAP1-38; a 38-amino-acid neuropeptide), along with its receptors, may be involved in the pathogenesis of migraine and cluster headache, as evidenced by elevated PACAP-38 plasma levels during ictal phases of both painful conditions [87,88,89,90]. This evidence concerns the gene ADCYAP1 and migraine disorder.