AEF0217 in Participants With Down Syndrome

This trial is a randomised, double blind, placebo controlled, parallel group, multicentre, Phase 2B trial.

Approximately 188 participants will be enrolled at clinical centres in Spain, France and Italy.

After the Day 1 visit (baseline) to the site and the Day 2 visit by phone/video, the trial will include 3 visits to the site during the treatment period, i.e., at the end of Weeks 4, 12, and 24, and there will be a follow-up visit 8 weeks after the end of treatment (in Week 32). Additional phone visits (via phone or video call) will be performed at the end of Weeks 1, 2, 8 and 18.

Participants completing 24 weeks of treatment will be invited to enter an open label 12-month extension trial (OLE) when it is approved and, if choosing to do so, will continue directly into the extension trial. . The participants who do not choose to enter the extension trial will enter the follow-up period. The participants that complete the trial, before the extension trial starts, may enter when it starts.

Safety assessments will be performed at each visit to the clinical site and include blood sampling for clinical chemistry, haematology and determination of AEF0217 and endocannabinoids concentrations at Weeks 12 and 24. In addition, urine samples will be collected.

Efficacy assessments will be performed during treatment at the end of Week 4 (adaptive behaviours, cognition and sleep efficiency), Week 12 (adaptive behaviours, cognition, quality of life, sleep efficiency and clinician functional assessment ), Week 24 (adaptive behaviours, cognition, quality of life, clinician functional assessment and sleep) and Week 32 at the end of the follow-up period (adaptive behaviours, cognition, sleep efficiency and clinician functional assessment) only for the participants who enter the follow-up period.

The total duration of the trial for an individual participant will be up to 36 weeks.

An independent (from the sponsor and the investigational centres) safety data monitoring committee (IDMC) will be set up in charge of performing an independent interim safety analysis at a minimum after 40 participants (at a minimum) have been treated for 12 weeks. The membership (including physicians with experience with Down syndrome and clinical pharmacologists), role and responsibilities of the IDMC will be defined in a specific charter before the trial starts. The IDMC will make recommendations related to any potential safety issues/signals to the Steering Committee of the trial (i.e., the coordinating investigator, the principal site investigator and responsible physician in each site and sponsor representatives

The trial will be conducted in accordance with the Declaration of Helsinki and ICH Good Clinical Practice.

Before initiating the trial, the clinical trial protocol, the written participant information and informed consent forms, the investigator's brochure, the recruitment material, and any other information for the participants and caregivers will be submitted to and approved by central ethic committees and national health authorities, as applicable.

Main Statistic analysis:

For the primary endpoint descriptive analysis will include: 1. The raw scores of the 9 subdomains of the VABS 3; 2. The raw scores of the 9 subdomains standardized to 100; and 3. Change from baseline to Week 24. These variables will be presented by treatment, dose, and visit (baseline and 24 weeks).

An MMRM will be used to evaluate the primary endpoint. The model will contain as dependent variable the change from baseline to Week 24 of the raw scores of the 9 subdomains of the VABS 3 standardized to 100 and as factors:

• Treatment (placebo, AEF0217)
• Dose (0 [placebo], 0.1, 0.2, 0.6 mg AEF0217) nested to treatment
• Subdomains: receptive, expressive, written, personal, community, domestic, interpersonal relationships, play and leisure time, coping skills
• Level of impairment at baseline
• Treatment interactions with subdomain and/or level of impairment at baseline.
• Dose interactions with subdomain and/or level of impairment at baseline

The model will use a restricted maximum likelihood (REML) method, and an unstructured covariance matrix will be used. If the model is not estimable, a compound symmetry structure will be used instead. The primary endpoint will be reached if there is a statistically significant (p<0.05) main effect of treatment or dose or any significant (p<0.05) interactions between treatment or dose and subdomain and/or the previous factors with the impairment at baseline.

For the other efficacy endpoints (secondary and exploratory) and pharmacodynamic endpoints the same model with the appropriate adaptations will be used as will be described in the SAP.

Safety endpoints: TEAEs will be reported in individual data listings and frequency tables. Based on reported terms, TEAEs will be coded in and tabulated by MedDRA SOC and PT. AEs will be classified based on severity (mild, moderate, severe) and causality (related or not related) and outcome.

Summary statistics of vital signs, ECG, and safety laboratory parameters (with flagging of values outside the normal ranges and considered clinically significant) will be provided.

Inclusion criteria

• 1. Male and female. For males: Throughout the trial and until the end of the trial, male participants should refrain from donating sperm and, if sexually active, use double-barrier contraceptive methods (i.e., male condoms and spermicide), or the female partner must use the same highly effective contraceptive methods as female trial participants .

For females: Female participants of childbearing potential, defined as having a menstrual cycle that is confirmed prior to enrolment, must use highly effective contraception throughout the trial and until 3 months after the last dose of the trial intervention, be sexually abstinent, or have a vasectomized partner.

• 2. Age ≥16 to ≤32years.
• 3. BMI ≥18.0 and ≤35 kg/m2.
• 4. Clinical diagnosis of Down syndrome (full trisomy 21 or translocations) documented by chromosomal analysis (karyotyping).
• 5. Must be independently mobile and have sufficient vision and hearing to participate in the trial evaluations.
• 6. IQ >35-70 measured with Leiter-3. Individuals with IQ from >35 to <40 must have adequate cognitive and behavioural abilities according to the judgment of the principal investigator.
• 7. VCI of WISC-V language test score >4, based on mental age (estimated via IQ).
• 8.Must be able to understand most of the time and to express if he/she does not understand to the extent that he/she can accept the trial procedures. Must not use other forms of communication, signs, symbol boards, or devices as his/her primary form of communication.
• 9. Must have a parent or other reliable caregiver who agrees to accompany the participant to all clinic visits, provide information about the participant as required by the protocol, and ensure compliance with the medication schedule and protocol requirements
• 10.The parent or caregiver must be a constant and reliable informant with sufficient contact with the participant to have detailed knowledge of the participant's adaptive functioning to be able to answer accurately the questions asked by a neuropsychologist at the assessments.
• 11. Vital signs, ECG , and safety laboratory3 parameters must be without clinically relevant abnormalities as per the judgement of the investigator, except for:

• Stable type 1 or 2 diabetes provided the participant is monitored regularly prior to and during the trial to ensure adequate glucose control.
• Hypothyroidism controlled by treatment so that the participant is euthyroid and T4 stable (range 77-155 nmol/L) for at least 6 weeks prior to randomization. Fluctuations in TSH up to a maximum of 10 mIU/L are allowed.
• 12. a. Assent by the participant and consent by the legally authorized representative(s) on behalf of the participant or b. Consent by the participant in situations where consent rather than assent can be provided by the participant.
• 13. Informed consent by the participant's caregiver to take on the obligations of the caregiver in this trial.

Exclusion criteria

• 1. Pregnant or nursing female. Down syndrome
• 2. Mosaic Down syndrome or Down Syndrome Regression Disorder (DSRD). Medical history and clinical status
• 3. Active or clinically relevant conditions that could, in the investigator's judgment, affect absorption, distribution, or metabolism of the trial medication (e.g., inflammatory bowel disease, gastric or duodenal ulcers or severe lactose intolerance); controlled celiac disease is allowed.
• 4. Clinically relevant obstructive pulmonary disease or asthma that is untreated. Patients well-controlled by treatment (inhalation or oral) for at least 6 weeks prior to screening may be included if considered safe by the investigator.
• 5. Known severe obstructive sleep apnoea or if the investigator thinks that the person should be referred for a diagnosis/treatment of obstructive sleep apnoea.
• 6. Recent (≤1 year) or ongoing haematologic or oncologic disorders (mild anaemia is allowed).
• 7. History of infantile spasms/convulsions/epilepsy, severe head trauma or central nervous system infections (e.g., meningitis), except for isolated events of febrile seizures more than 8 years ago.
• 8. Clinically relevant unstable gastrointestinal, renal, hepatic, endocrine (including metabolic syndrome), or cardiovascular system disease as per the investigator's judgement.
• 9. Any prevailing psychiatric disorder diagnosed using the DSM-5 that dominates a person's overall clinical condition outside of Down syndrome. If symptoms consistent with a diagnosis of psychiatric illness are detected during the screening assessment (NPI-Q) and considered as dominating, the investigator may request a psychiatric evaluation. If necessary, a consultant psychiatrist will be responsible for the final diagnosis, as this is not the investigator's responsibility.
• 10. Participants with secondary psychiatric disorders including conduct disorders, attention deficit hyperactivity disorder, depressive disorders, anxiety disorders, and others that: 1) dominate the overall clinical condition according to the investigator's assessment; and/or 2) are not stabilized by medical or behavioural treatments, a stabilized treatment being defined as a stable therapeutic regimen and dose for the 3 months prior to randomization; and/or 3) the type of pharmacological treatment is on the list of drugs that are prohibited.
• 11. Symptoms of early dementia confirmed by the NTG-EDSD.
• 12. Substance use disorder as defined by the DSM-5.
• 13. Positive urine test for alcohol and drugs of abuse at screening and prior to first dosing.
• 14. Current diagnosis of epilepsy.
• 15. A history of intentional self-harm or suicide attempts brought on by suicidal thoughts. Suicidal ideation in the 12 months before screening, even if there was no suicide attempt or intentional self-harm. Assessed using 3 distinct questions about suicidal behaviour, suicidal ideation, and any self-harming actions.
• 16. Known hypersensitivity to AEF0217 or fructose intolerance.
• 17. Clinically significant illness, such as active infections, within 2 weeks prior to randomization, according to the investigator's judgment.
• 18. Any current life-threatening disease.
• 19. Any additional clinically significant concomitant disease, condition, or screening result that, in the investigator's opinion, could endanger the participant's safety, interfere with trial conduct and related procedures, or influence how the trial results are interpreted.
• 20. Treatment with 1st generation neuroleptic drugs currently or within 3 months prior to randomization and benzodiazepines currently or in the 4 weeks prior to baseline assessments.
• 21. Intake of products containing EGCG (e.g., TEAVIGO, Mega Green Tea Capsules Life Extension, or Font-UP Grand Fontaine Laboratories) currently or during the last 4 weeks prior to the baseline assessments.
• 22. Treatment with medications or very regular consumption of fruits (i.e., pomelo/grapefruit) or natural remedies (i.e., hypericum preparations) known to strongly or moderately induce or inhibit CYP3A4/5 P450 isozymes..
• 23. Administration of an investigational medicinal product, including AEF0217, within the last 3 months prior to randomization.