ADCYAP1 and migraine disorder: Recent studies show diagnostic value of serum PACAP in non-traumatic osteonecrosis (Zhu et al. 2021), migraine (Yan et al. 2021), anxiety disorder (Ross et al. 2020), post-traumatic stress disorder (Wang et al. 2021), and multiple sclerosis (Al-Keilani et al. 2021).