Finally, in vitro work has found that in addition to degrading GLP-1 and GIP, DPP-4 also degrades orexin B [57], and so it is reasonable to predict that a DPP-4 inhibitor like saxagliptin will also raise circulating levels of this orexin, though the relevance of this to DOC is unclear, as only orexin A deficiency has been studied in the context of acute and chronic brain injury [19–21]. Here, HCRT is linked to ichthyosis.