Assessing impairment of executive function and psychomotor speed in premanifest and manifest Huntington's disease gene-expansion carriers.

Executive functions (EF) and psychomotor speed (PMS) has been widely studied in Huntington's disease (HD). Most studies have focused on finding markers of disease progression by comparing group means at different disease stages. Our aim was to investigate performances on nine measures of EF and PMS in a group of premanifest and manifest HD-gene expansion carriers and to investigate which measures were most sensitive for assessment of individual patients by analyzing frequencies of impaired performances relative to healthy controls. We recruited HD gene-expansion carriers, 48 manifest and 50 premanifest and as controls 39 healthy gene-expansion negative individuals. All participants underwent neurological examination and neuropsychological testing with nine cognitive measures. The frequency of impairment was investigated using cutoff scores. In group comparisons the manifest HD gene-expansion carriers scored significantly worse than controls on all tests and in classification of individual scores the majority of scores were classified as probably impaired (10th percentile) or impaired (5th percentile) with Symbol Digit Modalities Test (SDMT) being the most frequently impaired. Group comparisons of premanifest HD gene-expansion carriers and healthy controls showed significant differences on SDMT and Alternating fluency tests. Nevertheless the frequencies of probably impaired and impaired scores on individual tests were markedly higher for Alternating and Lexical fluency tests than for SDMT. We found distinct group differences in frequency of impairment on measures of EF and PMS in manifest and premanifest HD gene-expansion carriers. Our results indicate to what degree these measures can be expected to be clinically impaired.