Movement sequencing in Huntington disease.

OBJECTIVES: To examine longitudinal changes in movement sequencing in prodromal Huntington's disease (HD) participants (795 prodromal HD; 225 controls) from the PREDICT-HD study.
METHODS: Prodromal HD participants were tested over seven annual visits and were stratified into three groups (low, medium, high) based on their CAG-Age Product (CAP) score, which indicates likely increasing proximity to diagnosis. A cued movement sequence task assessed the impact of advance cueing on response initiation and execution via three levels of advance information.
RESULTS: Compared to controls, all CAP groups showed longer initiation and movement times across all conditions at baseline, demonstrating a disease gradient for the majority of outcomes. Across all conditions, the high CAP group had the highest mean for baseline testing, but also demonstrated an increase in movement time across the study. For initiation time, the high CAP group showed the highest mean baseline time across all conditions, but also faster decreasing rates of change over time.
CONCLUSIONS: With progress to diagnosis, participants may increasingly use compensatory strategies, as evidenced by faster initiation. However, this occurred in conjunction with slowed execution times, suggesting a decline in effectively accessing control processes required to translate movement into effective execution.