This study tests a new drug, BIA 28-6156, for Parkinson's disease in people with a specific gene change called GBA-PD. Parkinson's disease is a brain disorder that affects movement. This study checks if the drug works and is safe. There are two main parts: genetic screening and treatment. First, they check if you have the GBA1 gene change. If yes, you might join the treatment part. You'll either get BIA 28-6156 (10 mg or 60 mg) or a placebo, which is a harmless pill that looks like the real drug, but has no effect. The study lasts for 78 weeks with a follow-up of 4 weeks to check safety. You will keep taking your usual Parkinson's medicine.

• Must have Parkinson's for at least 1 year, but not more than 7 years.
• Need to attend multiple visits over the 78 weeks.
• No severe motor problems or major surgeries planned.

Consider joining if you meet the criteria and are okay with the study length.