MRGPRX2 and granular corneal dystrophy type II: In skin lesions of ACD, in addition to histamine (HST), proinflammatory cytokines, and prostaglandins (PGs), the highly expressed pro-adrenomedullin peptide 12 (PAMP12) stimulates, via Mas-related G-protein-coupled receptor member X2 (MRGPRX2), the augmented MCs to release tryptase β2.