In recent decades, the involvement of many genes and polymorphisms in the pathogenesis of overweight/obesity have been hypothesized, such as: tumor necrosis factor-α (TNFα), interleukin (IL)-6, methylenetetrahydrofolate reductase (MTHFR) and fat mass and obesity-associated (FTO) gene. Here, MTHFR is linked to obesity due to melanocortin 4 receptor deficiency.