Severity of cognitive impairment in juvenile and late-onset Huntington disease.

OBJECTIVES: To compare the severity of cognitive impairment among groups of patients with different age ranges at the onset of Huntington disease (HD) and to evaluate the variable influence of motor and cognitive deficits on functional disability across different ages at the onset of HD.

DESIGN: Cross-sectional multidisciplinary evaluation of patients referred to our institution for care related to a possible diagnosis of HD.

SETTING: The Huntington disease program in the Departments of Neurology and Genetics at the Fundación Jimenez Diaz, Madrid, Spain.

PARTICIPANTS: Seventy-one patients with Huntington disease were classified into 3 groups depending on age at onset of motor symptoms: juvenile onset, 25 years of age or younger (group 1, n = 15); adult onset, from 26 to 50 years (group 2, n = 43); and late onset, 51 years or older (group 3, n = 13). Age- and education-matched controls (n=50) were included to compare cognitive performance with patients in groups 1 and 3.

MEASURES: Cognitive evaluation encompassed a wide neuropsychological battery to assess global cognitive functioning and visuospatial, prefrontal, and memory functions. Clinical data included motor and functional variables measured by using the Unified Huntington's Disease Rating Scale. Genetic analysis determined the number of CAG trinucleotide repeats.

RESULTS: Patients in group 1 scored 2.9 points and patients in group 3 scored 4.2 points below their respective controls on the Mini-Mental State Examination. Patients in groups 1 and 3 were similarly impaired in verbal memory. Visual function was much more impaired in patients in group 3, and prefrontal functions were slightly worse in patients in group 1. Cognitive scores were correlated only with time of evolution for patients in group 2. Functional scores were not significantly different among the 3 groups, but 11 (85%) of the patients in group 3 were in stage I or II vs 10 (67%) of the patients in group 1. Total functional capacity correlated better with the Mini-Mental State Examination score for patients in group 3 and with motor deficits (akinesia) and prefrontal dysfunction for patients in group 1. The mean+/-SD CAG repeat length decreased from 59.9+/-12.6 for patients in group 1 to 46.2+/-3.5 for patients in group 2 and 41.7+/-2.6 for patients in group 3. Longer CAG repeats in the HD study population correlated with akinetic features but not with cognitive performance.

CONCLUSIONS: Despite the much greater genetic defect, cognitive status is slightly better preserved in patients with juvenile-onset HD. Cognitive impairment in patients with juvenile- and late-onset HD differs in the severity of visual and prefrontal deficits. Functional disability in patients with late-onset HD depends more on global cognitive status, while in patients with juvenile-onset HD, it is conditioned more by motor deficits and prefrontal dysfunction.