Motor changes in presymptomatic Huntington disease gene carriers

Objective: To determine whether changes in motor function and reaction time are present in presymptomatic individuals carrying the Huntington disease (HD) allele. Design: A case-control, double-blind study comparing asymptomatic at-risk subjects, with or without the HD allele, and subjects clinically determined to have early manifest HD. Setting: The Department of Medical and Molecular Genetics at Indiana University School of Medicine, Indianapolis. Participants: We studied 383 patients at risk for HD. Each subject was asymptomatic by self-report. Measures: Genotype for the I-ID allele was determined by polymerase chain reaction testing. A battery of 8 physiological tests measuring speed of movement and reaction time was performed with a computer-driven system. Results: Following neurologic examination, 17 of the 120 gene carriers (GCs) had symptoms sufficient for a clinical diagnosis of manifest HD. The remaining 103 GCs were designated presymptomatic GCs. When the non-GCs were compared with the presymptomatic GCs (1-way analysis of covariance and the Fisher protected t test), results on 3 of the 8 physiological tests-movement time, movement time with decision, and auditory reaction time-were different. Additionally, the number of trinucleotide (GAG) repeats significantly correlated with test performance for movement time with decision and visual reaction time with decision when both the entire group of GCs and the presymptomatic GCs alone were considered. Conclusion: These results suggest that subtle subclinical changes in motor function are present in presymptomatic individuals who have inherited the HD allele.