This is a phase 4, double-blind, placebo-controlled, randomised trial, multicentre study conducted in France to evaluate the efficacy and safety of glycopyrronium bromide (Sialanar®) versus placebo in addition to Standard of Care (SOC) management (rehabilitation) in children with severe sialorrhea related to chronic neurodisabilities, i.e cerebral palsy, Angelman syndrome, Rett's syndrome, epilepsy, amyotrophic lateral sclerosis and mental retardation. The patient population will be children aged from 3 to 17-year-old with severe sialorrhea due to chronic neurological disorders, defined as a score of at least 6 on the modified Teachers Drooling Scale (mTDS), after at least 3 months of non pharmalogical rehabilitation. A total of 80 patients who meet the eligibility criteria (see section 6.3) will be enrolled in the study. General eligibility criteria will be assessed and the DIS scale (French validated version) performed at the enrolment visit. Patients, enrolled in the study, will be randomized to receive the study drug in a doubleblind fashion, either Sialanar® of placebo. Eligible patients will be randomized in a 1:1 ratio into the 2- treatment arms with no additional stratification. Patients will receive the study drug, an oral solution, 3 times daily during the 3-month blind period. The titration will be performed during the first 5 weeks as detailed in section 7.1.3 Outpatient visits will occur at D28 and D84. Telephone interviews will occur every week during the titration period and at D56.

The double-blind placebo-controlled study duration will be scheduled for 3 months with the final visit of the double-blind period at D84. After the D84 assessment, patients will be invited to continue into a 6-month open-label study extension (OLSE) with ex-Sialanar® patients continuing the treatment and ex-placebo patients starting Sialanar®. An period of titration will be performed for patients starting Sialanar®, monitored by weekly telephone interviews. Telephone interviews will also be scheduled at D140. Clinic visit will be scheduled at D168 for all patients. Final OLSE visit will occur at D252. Patients will be assessed for disease response with the Drooling Impact Scale (DIS) including 10 items rated on a scale from 1 to 10 at D0 and during follow-up visits at D28, D84 and D252. Quality of Life will be evaluated through the DISABKIDS self-reported instrument completed by parents/ caregivers as well as children, when possible. Adverse events will be collected at every visit from parent or carer and participant where possible. All adverse events will be recorded at every scheduled visit plus outside of visits as required. All SAEs and SUSARs will be recorded and reported as per standard EMA guidelines (cf. Section 9.2).

The duration of the study will approximately be 15 months including 6 months of enrolment and 9 months of follow up from the last patient enrolled (3 months for the blind period and 6 months for the OLSE). The end of the blind period will correspond to the last patient completed D84 visit. The end of the OLSE will correspond to the last patient completed D252 visit. After all patients complete the blind period, the final analysis of the primary outcome (change in DIS at D84) will be performed. The follow up analysis of the OLSE period will be carried after all patients ended the study. All safety data will be analysed regardless of the outcome of the trial.