NTRK2 and obesity due to melanocortin 4 receptor deficiency: Mice with the conditional knockout of BDNF develop obesity and hyperactivity,52–54 with subsequent human studies showing a chromosomal inversion leading to the loss of one functional copy of BDNF in an 8-year-old girl; this resulted in increased food intake, severe early-onset obesity, hyperactivity, and cognitive impairment.55 In addition, a Y722C missense variant in NTRK2 has been reported in an 8-year-old boy with severe obesity and impaired memory.56