The primary objective of this study is to undertake a longitudinal investigation of the impact of sleep and circadian rhythm disturbances on cognitive and behavioural trajectories in children with autism spectrum disorder (ASD) age 3-10 years old.

This innovative study will use objective quantifiable measures of sleep and circadian rhythms in addition to subjective measures.

The investigators aim to assess the hypotheses that, in pre-pubertal children with ASD,

1. sleep disturbances are correlated with circadian rhythm disturbances;
2. both sleep and circadian rhythm disturbances are negatively correlated with cognitive performance and positively correlated with behavioural disturbances;
3. sleep and circadian rhythm disturbances, most notably abnormal melatonin secretion, impact the cognitive and behavioural development of children with ASD, depending on age (prospective longitudinal analyses).

Inclusion criteria:

• Age: from 3 to 8 years of age at inclusion, as per defined entry ages (longitudinal accelerated design)
• Diagnostic criteria of autism spectrum disorder (ASD)
• Autism Diagnostic Interview (ADI) - revised (R) score compatible with ASD diagnosis
• Autism Diagnostic Observation Schedule (ADOS) score compatible with ASD diagnosis
• Study information has been understood
• Study consent signed by both parents or legal representatives and by the child if the child is capable of expressing his consent
• Stable medication over the 2 months-period preceding inclusion and during evaluation periods (exception: (1) medication mentioned in the exclusion criteria, (2) a new medication instaurated between two evaluation periods is not in itself an exclusion criteria, but will be taken into account in data analysis)
• Compliance with study procedures
• Priori clinical medical examination
• Child affiliated with social security Concerning sleep disorders: the discovery of a primary sleep disorder (e.g.: sleep apnea syndrome, restless legs syndrome, periodic limb movements during sleep) as well as their treatment is not a criteria for terminating the study but will be taken into account in data analysis

Exclusion criteria:

• Secondary autism: e.g. associated with Rett syndrome, fragile X syndrome, Down syndrome, Bourneville tuberous sclerosis, von Recklinghausen disorder, Cytomegalovirus (CMV) encephalitis, congenital rubeola, phenylketonuria.
• Current treatment with melatonin or melatonin agonists before study entry (before baseline assessment)
• Changes in medication over the 2 months-period preceding the study (exception: a new medication instaurated between two evaluation periods is not in itself an exclusion criteria, but will be taken into account in data analysis)
• Transmeridian travel (> 2 time zones) in the month preceding the study
• Participation in other research studies in the 3 months period preceding the study
• Treatment with betablockers, local or systemic non-steroidal anti-inflammatory (NSAI) agents, benzodiazepines, antidepressants
• Severe other intercurrent disorder.
• Severe allergies.