Prader-Willi syndrome: the psychopathological phenotype in uniparental disomy.

P rader-Willi syndrome (PWS) is a neurogenetic disorder resulting from the absence of a normal paternal contribution to the chromosome 15q11-13 region. The clinical manifestations of PWS are: reduced fetal activity during pregnancy, a transient severe hypotonia and feeding problems in the neonatal period, a variable degree of mental retardation, hyperphagia, obsessive compulsive features such as skin picking, and a variety of hypothalamic dysfunctions. The latter become manifest as hypogonadism, short stature, sleep disturbances, and defects in temperature regulation. In addition, post mortem studies reveal a significantly lower number of small oxytocin secreting neurones in the paraventricular hypothalamus and, in some cases, a reduction of vasopressin secreting neurones as well as diminished vasopressin precursor processing. 2 Apart from the behavioural problems associated with food seeking and intellectual disability per se, PWS carries the risk of obsessive compulsive disorder, mood abnormalities and psychotic disorders. Given the high prevalence of these psychiatric symptoms, the term psychopathological phenotype is justified.