Study Overview: This study aims to see if a smartphone app can help people with specific genetic mutations (LRRK2 G2019S or GBA1 N370S) exercise more, to potentially slow early Parkinson's disease. Parkinson's is a brain disease that affects movement and usually gets worse over time. Study Design: Participants will use a special app to track their exercise for 36 months (3 years). They'll be asked to increase their daily steps and exercise minutes. The app will guide them on how much to increase, based on their starting activity levels. The study will see if the app helps them stick to the plan and if exercise affects early signs of Parkinson's. Key Points: - **Length of Study:** Participation lasts for 3 years, with ongoing monitoring through the smartphone app. - **Participation Requirements:** Participants need to be at least 50 years old, speak English, and have a smartphone that works with the study's app. - **Compensation and Risks:** The study does not mention specific compensation but involves a commitment to increase physical activity, which carries typical exercise risks. This is a double-blind study, meaning neither participants nor researchers know who's in which group, to ensure unbiased results. Participants will be recruited mainly from the 23andMe customer base and must meet specific criteria to join.