It is noteworthy that an enzyme semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1), which is responsible for deamination of the primary amines such as methylamine and converts them into cytotoxic aldehydes, e.g., formaldehyde, ammonia, and hydrogen peroxide, is found to be associated with obesity and related diseases. Here, AOC3 is linked to obesity due to melanocortin 4 receptor deficiency.