**GBPDC: Gut-Brain in PD Consortium Master Protocol** This research study is looking at how the gut-brain connection affects Parkinson's Disease (PD). The gut-brain axis is a system of nerves linking the gut and brain. The study is sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases. Participants are divided into groups based on their PD stage, those at risk for PD, and those without PD. The study lasts up to 24 months, and participants will visit medical providers, fill out surveys, and provide samples like blood and saliva. They will also undergo tests such as X-rays and a flexible sigmoidoscopy, where a doctor looks inside the lower colon and takes small tissue samples. **Key Points:** - Participation lasts up to 2 years with visits at 6, 12, 18, and 24 months. - Tests include providing samples, X-rays, and a colon examination. - Suitable for ages 21 to 80, with specific health criteria. Participation helps understand PD better, but includes several tests and regular visits over two years.