Obesity-prone SR mice showed further downregulation of Slc25a13, Slc25a21, as well as Slc25a2 (a transporter of the positively charged amino acids ornithine, lysine, and arginine), Slc25a4 and Slc25a31 (which enable ATP/ADP antiporter uncoupling activity), Slc25a22 (an import of glutamate), and the unique upregulation of Slc25a1 (citrate export in exchange for malate). Here, SLC25A21 is linked to obesity due to melanocortin 4 receptor deficiency.