MC4R and obesity due to melanocortin 4 receptor deficiency: For example, eight genes have been reported as causes for obesity, including leptin (LEP), the leptin receptor (LEPR), proopiomelanocortin (POMC), prohormone convertase 1 (PCSK1), the melanocortin 4 receptor (MC4R), single-minded homolog 1 (SIM1), brain-derived neurotrophic factor (BDNF), and the neurotrophic tyrosine kinase receptor type 2 gene (NTRK2) [8,9], from over 500 obesity-related genes [5].