Daridorexant to Treat Insomnia in Patients With Mild Cognitive Impairment and Mild to Moderate Alzheimer Disease

Inclusion criteria : * Age \[60-85\] years old * Outpatients * Pre-screening: * Complaints of dissatisfaction with sleep quantity or quality, despite adequate opportunity for sleep, at least 3 nights per week and for at least 3 months, and * Total sleep time causes clinically significant distress or impairment in daytime functioning, and * Total sleep time estimated by interview was below 6 hours, on at least 3 nights per week and for at least 1 month before screening * Baseline PSG (at randomization) assessed TST \< 6 hours and WASO \> 1 hour * Diagnosis of MCI and AD patients at an early stage according to the NIA diagnosis criteria (core clinical criteria for MCI, positive CSF Aβ42 and/or positive plasma biomarker, and neuronal injury (hippocampal and/or temporal atrophy by MRI)) * MMSE from 12 to 26 * Clinical Dementia Rating CDR from 0.5 to 2 * Use of CNS-active medications is permitted provided the dose has been stable for at least 3 months, including: anticholinesterase drugs (rivastigmine, donepezil, galantamine) or memantine, antidepressants SSRI (e.g. fluoxetine, sertraline, paroxetine…), SNRI (e.g. venlafaxine, duloxetine), neuroleptics (e.g. clozapine, olanzapine, aripiprazole...) or drug for pain level 2 (codeine, tramadol). * For a male subject who is not sterilized and is sexually active with a female partner of childbearing potential, no contraceptive methods are needed Non inclusion criteria : * Patients significantly dependent on caregivers * Institutionalized patients * Analphabetism or subjects unable to read or/and write * Patients unable to perform the neuropsychological tests * Patients unable to complete the study instruments (sleep diary) * Planned longer stay outside the region that prevents compliance with the visit schedule * Patients who cannot be followed up for at least 2 months * History of narcolepsy and/or cataplexy * History of drug or alcohol abuse or addiction * History of diagnosed and characterized psychiatric disorders (DSM-5), cured or stabilized (with or without the same treatment for at least 3 months) and excluding any current characterized psychiatric disorder (DSM-5), the diagnosis of which is established by a psychiatrist trained in geriatric psychiatry * Moderate and severe liver failure * PSG baseline evidence of significant/severe sleep-related breathing disorder (defined as \>30 apnea/hypopnea episodes per hour) * Treatments interfering with sleep-wake patterns * Use of hypnotics (benzodiazepines, zolpidem, zopiclone) or drug for pain level 3 (morphine and derivatives) * Hypersensitivity to the active substance or to any of the excipients listed in the Summary of Product Characteristics (SmPC) * Forbidden and restricted concomitant medications: * Concomitant CNS-depressant medicinal products * CYP3A4 inhibitors * CYP3A4 inducers * Participation in another clinical trial or administration of an investigational product * Protected population according to articles of the French Public Health Code (e.g. patients under law protection, prisoners, pregnant, parturient or lactating women, and patients under guardianship/curatorship). * Subjects not covered by public health insurance * Failure to obtain written informed consent after a reflection period