Objective: To determine whether asymptomatic individuals at very high genetic risk for Huntington's disease (HD) have demonstrable cognitive or oculomotor abnormalities.
Design: A case-control study was employed. Presence of the chromosome-4 DNA marker linked to the HD phenotype was the criterion for HD risk.
Setting: The Baltimore Huntington's Disease Project Presymptomatic Testing Program at The Johns Hopkins University School of Medicine, Baltimore, Md.
Participants: Seventy-six asymptomatic adults at risk for HD, voluntarily enrolled for genetic testing, and determined by clinical examination to be free of major psychiatric disorder or evidence of HD. Twenty were determined to be at greater than or equal to 95% risk for HD; 56 were at less than or equal to 5% risk [corrected].
Measures: The Hopkins Verbal Learning Test was used to assess verbal learning and memory. Oculomotor functioning was assessed using Novel-Stimulus, Mirror-Stimulus, and Predictive-Saccade paradigms. Outcome measures included number of correctly recalled words, recognition accuracy, and response bias, as well as saccade latency and number of errors on the Mirror-Stimulus Test.
Results: With one exception, all participants performed within the normal range on the Hopkins Verbal Learning Test. In a blind follow-up examination of the individual who performed aberrantly on the Hopkins Verbal Learning Test, she exhibited neurologic and psychiatric changes sufficient for a clinical diagnosis of HD. There were no group differences on the tests of oculomotor functioning.
Conclusions: Young, asymptomatic adults at very high genetic risk for HD are unimpaired in tests of verbal learning and memory and oculomotor functioning.