SIM1 and obesity due to melanocortin 4 receptor deficiency: Some of the genes associated with monogenetic severe obesity are: leptin (LEP), leptin receptor (LEPR), proopiomelanocortin (POMC), MC4R, preproconvertase 1 (PCSK1), single minded 1 (SIM1), brain-derived neurotrophic factor (BDNF), and tyrosine kinase receptor tropomycin-related kinase B (TrkB) (Ramachandrappa and Farooqi, 2011).