BACKGROUND AND OBJECTIVES:Patients with Prader-Willi syndrome (PWS) display poor feeding and social skills as infants and fewer hypothalamic oxytocin (OXT)-producing neurons were documented in adults. Animal data demonstrated that early treatment with OXT restores sucking after birth. Our aim is to reproduce these data in infants with PWS.

Prader-Willi syndrome (PWS), first described in 1956, is considered as a paradigm of a neurodevelopmental disorder with severe and early obesity with hyperphagia and impaired satiety. The improved knowledge in the natural history and recent data on genetics offer new perspectives for understanding the metabolic and endocrine dysfunctions and possibly for treatment. Natural history of the disease has been described due to the early diagnosis performed in the first months of life and various nutritional phases have been described. In addition, there is clear evidence that the abnormal feeding behavior is included in the behavioral problems. Brain imaging studies have shown that some brain regions may be important in PWS. The role of SNORD116 gene cluster is detailed and its links with circadian rhythm and brain and hypothalamus development. Pathophysiology of the abnormal ghrelin levels and of OT dysfunction is documented. While no effect on appetite and weight regulation has been reported with ghrelin antagonists, OT has been shown to improve some of the behavioral problems in adults. We discuss our hypothesis of an abnormal ghrelin/OT/dopamine pathway which may explain the switch of nutritional phases and behavior. These new aspects offer an opportunity for therapeutic use and possible early intervention.

Background: People with Prader-Willi Syndrome (PWS) experience great difficulties in social adaptation that could be explained by disturbances in emotional competencies. However, current knowledge about the emotional functioning of people with PWS is incomplete. In particular, despite being the foundation of social adaptation, their emotional expression abilities have never been investigated. In addition, motor and cognitive difficultiescharacteristic of PWS-could further impair these abilities. Method: To explore the expression abilities of children with PWS, twenty-five children with PWS aged 5 to 10 years were assessed for 1) their emotional facial reactions to a funny video-clip and 2) their ability to produce on demand the facial and bodily expressions of joy, anger, fear and sadness. Their productions were compared to those of two groups of children with typical development, matched to PWS children by chronological age and by developmental age. The analyses focused on the proportion of expressive patterns relating to the target emotion and to untargeted emotions in the children's productions. Results: The results showed that the facial and bodily emotional expressions of children with PWS were particularly difficult to interpret, involving a pronounced mixture of different emotional patterns. In addition, it was observed that the emotions produced on demand by PWS children were particularly poor and equivocal. Conclusions: As far as we know, this study is the first to highlight the existence of particularities in the expression of emotions in PWS children. These results shed new light on emotional dysfunction in PWS and consequently on the adaptive abilities of those affected in daily life.

Dys-synchrony can be induced by children's pathology as well as parental pathology with emotional and developmental impact in the both cases. The PWS paradigm shows us the necessity to sustain early parents-child relationship to avoid establishment of a negative transactional pattern of interaction that can impact child's development.