Cognitive deficits predict poorer functional capacity in Huntington's disease: but what is being measured?

Huntington's disease (HD) is an inherited movement disorder characterized by choreiform movements and frontostriatal dysfunction. Previous studies have documented executive deficits in HD. We aimed to investigate the effect of cognitive deficits on patients' daily functioning. Furthermore, we sought to explore how independent patients' cognitive difficulties were from their motor and psychiatric symptoms.

We administered a battery of neuropsychological tasks assessing broader cognitive abilities and executive functions (e.g., verbal fluency, working memory, response inhibition) to 25 patients with HD and 20 healthy controls. Clinical ratings of functional capacity and the severity of motor and psychiatric symptoms were also taken. After establishing that patients with HD demonstrated characteristic cognitive deficits, we explored relationships between performance on neuropsychological tasks and clinical ratings.

Patients with HD exhibited deficits on all timed neuropsychological tasks but not on measures of accuracy. Poorer functional capacity was related to cognitive deficits and more severe motor symptoms. Motor and psychiatric symptoms were also related to cognitive performance. Category fluency scores alone predicted 54% of the variance in functional capacity.

Patients with HD exhibited a pattern of cognitive dysfunction that may reflect a generalized slowing in processing. It is important to note that we found that certain cognitive measures may help predict functional capacity in HD. However, we also highlight that performance on neuropsychological tasks can be influenced by motor or psychiatric symptoms. Future studies should consider such confounds when seeking purer measures of cognitive capacity.