Given the fact that ACTH is not the predominant POMC-derived peptide produced by the equine PI, the choice of this hormone as the preferred biomarker rather than any of the other PI products might seem illogical; however, this choice is likely due to ACTH assays being readily available commercially, the lack of availability of assays for other PI-derived peptides outside of the research setting and, potentially, the incorrect historical assumption that PPID was analogous to pituitary-dependent hyperadrenocorticism in other species [57]. This evidence concerns the gene POMC and Cushing syndrome.