The study did not received the approbation from Swissmedic. Therefore, the recruitment of participants never started.

Lennox-Gastaut syndrome is a severe epileptic encephalopathy of childhood. In that syndrome, various type of seizure occur, mainly tonic seizures, atonic seizures and atypical absences. The tonic seizure occur mostly at night.

The hypothesis is that the melatonin could have a positive effect in that syndrome, by reducing the epileptic activity (assessed in the polysomnographic record by counting the number of interictal and ictal discharges) and stabilizing the structure of sleep.

The study is double blind, randomised, cross-over designed.

The aim of the trial is to study the efficacity of melatonin in the Lennox-Gastaut syndrome, by assessing the reduction of the seizure/interictal discharges in polysomnography and assessing the sleep structure.

After initial recruitment, the baseline visit includes a polysomnography. The patients will then be randomised in two groups: melatonin (1 cp containing melatonin 2 mg 1x/d 1h before sleep) vs placebo (1 cp 1x/d 1h before sleep). The treatment (melatonin or placebo) will be given for 1 month.

After 1 month, the treatment will be stopped and another polysomnography will be recorded.

The patients will take no treatment (wash-out period) for 15 days. The second treatment phase is cross-over: the group that had melatonin in the first phase will take placebo for one month, and the group that had placebo in the first treatment phase will take melatonin for one month. A last polysomnography will be recorded after the second treatment phase.

The other medications (antiepileptic drugs) taken by the patients before the trial will not be modified.

Inclusion Criteria:

• Lennox-Gastaut syndrome (based on ILAE classification, 1989)
• light mental retardation (QI 50-69)
• french mother tongue
• having someone helping the patient (parent and/or referent educator)
• informed consent have been given by the patient / guardian
• absence of concomitant evolutive affection or associated sleep pathologies
• collaboration of the patient, ability to complete all aspects of the trial.

Exclusion Criteria:

• epileptic syndrome other than Lennox-Gastaut, other neurologic and/or psychiatric disease
• moderate to severe mental retardation (QI < 50)
• psychiatric disease that could interfere with the diagnostic procedure
• specific sleep disorder (anamnestic and diagnosed on the polygraphic record), for example: sleep apnea syndrome, narcolepsy, restless legs syndrome, periodic legs movements, etc...