From these results of our studies on IH-treated neuronal and enteroendocrine cells, IH observed in SAS patients up-regulates the expression of POMC and CART mRNAs in neuronal cells and PYY, GLP-1, and NTS mRNAs in enteroendocrine cells; therefore, it is possible that IH itself suppresses SAS patients’ appetite through the gut–brain axis (Figure 2). Here, PYY is linked to isolated hemihyperplasia.