LoF mutations or deletions of RAI1 are the cause of Smith–Magenis syndrome (SMS; MIM 182290), a complex disorder characterized by ID, sleep disturbance, multiple congenital anomalies, obesity, and neurobehavioral problems [17–21], whereas duplications of RAI1 are associated with a developmental disorder characterized by hypotonia, failure to thrive, ID, ASD, and congenital anomalies [22, 23], designated Potocki–Lupski syndrome (PTLS; MIM 610883). The gene discussed is RAI1; the disease is obesity due to melanocortin 4 receptor deficiency.