1 Introduction Smith–Magenis syndrome (SMS, OMIM 182290) is a relatively common syndrome (prevalence 1/15,000 to 1/25,000 in the general population), characterized clinically by a distinctive facial appearance (Figure 1), minor skeletal features (brachycephaly, brachydactyly, and scoliosis), hypercholesterolemia, developmental delay of varying degrees, global cognitive impairment greatest in the speech/language realm, sleep disturbance associated with abnormal diurnal melatonin release, and a...