PCSK1 and obesity due to melanocortin 4 receptor deficiency: Mutations in leptin (LEP), prohormone convertase 1 (PCSK1), proopiomelanocortin (POMC) and melanocortin 4 receptor (MC4R) are involved in rare monogenic recessive forms of obesity [5], but studies relying on populations with morbid obesity may not represent processes contributing to overweight and obesity in the general population.