EXT1 and obesity due to melanocortin 4 receptor deficiency: Mice with obesity or deletion of the myeloid-cell HS biosynthesis gene exostosin-1 (Ext1) show lower HS levels in WAT macrophages, leading to decreased intercellular mitochondrial transfer from adipocytes to macrophages, which in turn leads to weight gain and impaired glucose tolerance and insulin sensitivity (Figure 2) [88,131].