Objective: To describe the launch of Slow-SPEED-US, presenting recruitment results and baseline characteristics of the enrolled subsample.

Background: Slow-SPEED-US is part of a network of Slow-SPEED (Slowing Parkinson’s Early through Exercise Dosage) trials spanning the Netherlands, United Kingdom, and United States that are investigating a remotely delivered, unsupervised exercise intervention in individuals at increased risk for Parkinson’s disease (PD) due to clinical or genetic status.

Method: Slow-SPEED-US is a three-year, double-blind, randomized controlled trial. We will enroll up to 600 participants ≥ 50 years of age with a LRRK2 and/or GBA1 variant, no history of neurodegenerative disease, and a mean step count < 10,000 steps/day. Eligibility is determined through a telephone screening, followed by a 4-week assessment of baseline step count using a wrist-worn Fitbit. All eligible participants receive the gamified, motivational Slow-SPEED application and are randomized 1:1 to the intervention arm (100% increase in step count) or the active control arm (10% increase in step count). Participants complete questionnaires annually and digital motor assessments every 6 weeks. The primary objectives are to determine if the intervention slows progression on a novel digital prodromal load score and to determine the feasibility of the remote, unsupervised exercise intervention.

Results: 23andMe Research Institute invited 9,717 LRRK2 G2019S and GBA1 N370S carriers over the age of 50 years without self-reported Parkinson’s disease via e-mail outreach to participate. Of these, 209 unique participants completed a study interest form. Since September 2025, 135 (65%) have completed a telephone screening, and 81 (39%) provided consent. As of March 3, 2026, 60 have completed their 4-week assessment period and 11 (18%) have been excluded due to a high baseline step count. Thus far, 41 participants (mean (SD) age 64.1 (±8.6), 29 (71%) female, 16 (39%) LRRK2 carriers, 25 (61%) GBA1 carriers with 5615 (±1797) steps/day and 29.9 (±37.8) minutes/day of moderate-to-vigorous physical activity) have been randomized.

Conclusion: Slow-SPEED-US has successfully launched and is poised to test the preliminary efficacy and feasibility of a remotely delivered, unsupervised exercise intervention in LRRK2 and GBA1 carriers at increased PD risk. We will triangulate results with ongoing studies in the Netherlands and the United Kingdom to maximize learnings.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/slow-speed-us-initiation-of-a-remote-exercise-trial-in-lrrk2-and-gba1-carriers/