Hyperphagia, severe obesity, impaired cognitive function, and hyperactivity associated with functional loss of one copy of the brain-derived neurotrophic factor (BDNF) gene Hyperphagia, severe obesity, impaired cognitive function, and hyperactivity associated with functional loss of one copy of the brain-derived neurotrophic factor (BDNF) gene Diabetes Diabetes 2006 2006 55 55 3366 3366 3371 3371 17130481 17130481. Here, BDNF is linked to obesity due to melanocortin 4 receptor deficiency.