ADCYAP1R1 and posterior polymorphous corneal dystrophy: Due to the scarcity of corneal endothelial tissue from affected individuals, we assessed protein expression of one epithelial-associated protein, claudin 1 (CLDN1), and of one endothelial-associated protein, adenylate cyclase activating polypeptide 1 receptor type 1 (ADCYAP1R1), in PPCD endothelium (Fig 1F).