AQP8 and obesity due to melanocortin 4 receptor deficiency: The crucial genes of aquaporin 8a (aqp8), mucin 2.1 (muc2.1), fibroblast growth factor 2 (fgf2), and proopiomelanocortin a (pomca) can indicate the intestinal secretory and absorptive-, and obesity-related functional abnormality in the host (Campion et al., 2009; Dotti et al., 2017; Montalbano et al., 2018).