OXT and Prader-Willi syndrome: PWS is due to the absence of expression of maternally imprinted gene(s),38 a class of genes known to drive placental–foetal nutritional pathways.39 Intranasal oxytocin is being tried experimentally to treat various aspects of the early and later PWS phenotypes, including the hyperphagia, and growth and sex hormone replacement therapy is now routine, both seeking to compensate for the deficits of hypothalamic origin.