This clinical trial is focused on studying *Gaucher disease Type 3*, a rare genetic disorder that affects various parts of the body, including the brain. The study aims to evaluate the effectiveness and safety of a medication called *venglustat* (also known by its code names GZ402671 and SAR402671) in both adults and children who have been managing their condition with a treatment known as *Enzyme Replacement Therapy* (ERT). The trial will compare *venglustat* to another treatment called *Cerezyme*, which is a form of ERT that contains the active substance *imiglucerase*. Participants in the study will receive either *venglustat* or *Cerezyme*, and some may receive a placebo.
The purpose of the study is to see how well *venglustat* works in improving symptoms of *Gaucher disease Type 3*, such as problems with movement and thinking skills. The study will look at changes in movement using a tool called the Scale for the Assessment and Rating of Ataxia (SARA) and changes in thinking skills using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Participants will be monitored over a period of time to assess these changes and to ensure their safety while taking the medication.
Throughout the study, participants will have regular check-ups to monitor their health and any changes in their condition. The study will also track other health indicators, such as spleen and liver size, blood levels, and any side effects that may occur. The trial is designed to provide valuable information on whether *venglustat* can be a safe and effective treatment option for people with *Gaucher disease Type 3*.



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