Inclusion Criteria:  Genetically confirmed Smith Magenis syndrome (microdeletion of the short arm of chromosome 17 or mutation of the RAI1 gene; obtained by FISH, CGH-array or molecular biology) Aged 7-12 years Consent form signed by the parent(s) Requiring a sleep assessment in the Hopital Femme Mère Enfant paediatric sleep unit of Pr Franco Affiliation to a social security system.  Exclusion Criteria:  Associated ophthalmological disorders that do not allow the photomotor reflex to be studied: optic neuritis, glaucoma and retinitis pigmentosa. Dyschromatopsia detected in consultation with a rapid Ishihara test adapted to the child's cognitive level, if necessary supplemented by a test performed by ophthalmologists. Algic child (risk of measurement bias: when a patient is in pain his pupils dilate and we observe a greater amplitude in the photomotor reflex), defined by a score on the FPS-R Face Scale >4/10.