Prader-Willi psychiatric syndrome and Velo-Cardio-Facial psychiatric syndrome: Similar to the studies on behavioural phenotypes, it is suggested to more rigorously promote the investigation of psychopathological phenotypes. The psychopathological profile in patients with Prader-Willi Syndrome (PWS) or Velo-Cardio-Facial Syndrome (VCFS) appears to be not classifiable within the current nosological systems. On a descriptive level, PWS-psychotic states show similarities with the cycloid psychoses, but VCFS psychosis does not. It is therefore advocated to adopt the notion of a brain-structure phenotype as well as that of a syndrome-specific psychiatric disorder.