title: Thoughts on the behavioural phenotypes in Prader-Willi syndrome and velo-cardio-facial syndrome: a novel approach.
abstract: BACKGROUND
  In both Prader-Willi syndrome (PWS) and 22q11 deletion syndrome [velo-cardio-facial syndrome (VCFS)], an increased risk for psychotic disorders is reported, which are as a rule not included in the behavioural phenotype of these two syndromes. For the description of a behavioural phenotype, the complete spectrum of physical, developmental, neuropsychological and psychiatric aspects is generally not taken into account. Moreover, psychiatric signs and symptoms often do not meet the criteria for a categorical diagnosis.
  
  
  OBJECTIVE
  In this study, a further specification of psychotic symptoms in PWS and VCFS is shown as well as a proposal for a new model to ascertain predictors, including behavioural, for a genetic syndrome.
  
  
  METHODS
  Over the past years, 27 patients with PWS and 19 with VCFS were referred for neuropsychiatric evaluation because of psychotic symptoms. In all the patients, a standardised psychiatric examination was performed; seven of the patients with VCFS were evaluated by means of an extensive neuropsychological battery.
  
  
  RESULTS
  In both patient groups, a rather specific psychopathological profile seemed to be present, which in the case of patients with PWS showed some resemblance with bipolar affective disorder. In patients with VCFS, no formal psychiatric diagnosis could be established. Because the psychopathological profiles were rather aspecific, they are not sufficient to predict membership of a certain syndrome.
  
  
  CONCLUSIONS
  A quantitative probabilistic approach toward the description of a (behavioural) phenotype is suggested. For such a procedure, large data sets and international collaboration are required.
authors.affiliation: 1Vincent van Gogh Institute for Psychiatry, Venray, The Netherlands.
authors.forename: Willem
authors.initials: W
authors.lastname: Verhoeven
authors.affiliation: 1Vincent van Gogh Institute for Psychiatry, Venray, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Egger
authors.affiliation: 1Vincent van Gogh Institute for Psychiatry, Venray, The Netherlands.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Tuinier