In view of the reports documenting that BDNF+/- mice exhibit growth retardation, obesity, hyperactivity and aggressiveness [7-10], we felt it was critical to assess these parameters in our cKO mice that accumulate hippocampal BDNF to 50% of the levels observed in WT animals. The gene discussed is BDNF; the disease is obesity due to melanocortin 4 receptor deficiency.