GFPT1 and obesity due to melanocortin 4 receptor deficiency: The reason behind this difference is entirely unexplored but may be partly related to alternative regulation of flux through the HBP via GFAT phosphorylation or isoform expression or the obesity-linked enzyme that can counteract GFAT, Gnpda (Oikari et al. 2016; Oki et al. 1999; Schleicher and Weigert 2000; Ouyang et al. 2016).