The ADRB3 rs4994 polymorphism (Trp64Arg), a T to C switch leading to the replacement of tryptophan by arginine at position 64, has been related to lower resting metabolic rate [9], weaker response to obesity treatment [10], and increased capacity to gain weight [11] according to scattered evidence. This evidence concerns the gene ADRB3 and obesity due to melanocortin 4 receptor deficiency.