OGT and obesity due to melanocortin 4 receptor deficiency: Another X-linked gene is O-GlcNAc transferase (OGT), although its functions on body weight balance appears to be site specific, with OGT in orexigenic agouti-related peptide (AgRP) neurons promoting weight gain (Ruan et al., 2014) while OGT in anorexigenic PVH neurons prevent overeating and obesity (Lagerlof et al., 2016).