Prader-Willi Syndrome (PWS) is a rare neurodevelopmental disorder stemming from genetic damage in the 15q11-q13 region, leading to hypothalamic dysfunction. Individuals with PWS often exhibit social interaction challenges, intellectual deficits, significant eating disorders, mood disturbances, and sensory-related autistic features. Although PWS is recognized by DSM-5 as a genetic cause of Autism Spectrum Disorder (ASD), ASD diagnosis in PWS remains rare in France. The CASSPER study aims to investigate the distinct autistic and sensory profiles in children with PWS, also analyzing the potential impact of early oxytocin treatment on these manifestations, in line with recommendations for early and tailored intervention.

Prader-Willi syndrome (PWS) is a rare and complex neurodevelopmental disorder (NDD) with genetic origin linked to chromosomal damage in the 15q11-q13 region and characterised by hypothalamic dysfunction. At the psychiatric level, patients with PWS display difficulties in social interaction, mild to moderate intellectual deficit, major eating disorders, mood disorders and autistic manifestations, including hypo-/hyper-reactivity to sensory stimuli.

While the International Classification (DSM-5) lists PWS as one of the genetic causes of Autism Spectrum Disorder (ASD), little is known about the interaction between autistic traits, sensory features and PWS.

To date, assessment and diagnosis of ASD in PWS remains exceptional in standard care in France, despite the obvious importance of correct assessment for early identification and intervention.

In this context, the CASSPER study aims to identify the specificity of PWS in terms of autistic symptomatology and sensory characteristics. The CASSPER study is in line with the recommendations of the French National Health Authority (HAS) for early and appropriate guidance of children with PWS.

In addition, almost all children with PWS under the age of 5 have received early treatment with oxytocin (OT). As the neuromodulatory effect of OT treatment and the involvement of this neurohormone in the development of attachment, social interaction and sensory processing may explain a difference in autistic symptomatology, this parameter will be included in the analyses.

The CASSPER study aims to fill gaps in our knowledge of PWS and its care and could be useful more generally to improve our understanding of autistic manifestations in NDD of genetic origin.

Inclusion Criteria:

• Child with genetically confirmed PWS and identification of genetic subtype;
• Child aged between 3 and 16 years;
• Hospitalisation or multidisciplinary consultation planned for the child's routine follow-up at one of the investigating centres;
• No parental/legal guardian objection.

Exclusion Criteria:

• Change in psychotropic treatment (start, change in dose or discontinuation) in the past 3 months;
• Inability to provide clear information to parents/legal guardian;
• Not covered by social security.

The study population consists of children aged 3 to 16 years who have been diagnosed with Prader-Willi syndrome through genetic confirmation, recruited from several hospital centers in France.