ADRB2 and obesity due to melanocortin 4 receptor deficiency: The Gly16Arg (G/C) substitution of ADRB2, which appears to be of significant importance to ADRB2 function, at least in fat cells, but less so for obesity, may induce a significant decrease in agonist affinity for ADRB2 and/or a significant increase in ADRB2 downregulation [41,50].