LDLR and obesity due to melanocortin 4 receptor deficiency: Key regulator proteins from lipid biosynthetic pathway, including hydroxymethylglutaryl-CoA synthase (HMGCS1) and low-density lipoprotein receptor (LDLR) were found to be downregulated in myotubes from donors with obesity compared to cells from lean donors (Figure 1; Supplementary Table S2).