Is Huntington's disease associated with deficits in theory of mind?

OBJECTIVES: People with Huntington's disease (HD) can exhibit interpersonal difficulties and deficits in recognizing emotional facial expressions. We investigated whether individuals with HD exhibit impairments in the understanding of other people's mental states, an aspect of Theory of Mind (ToM).
MATERIALS AND METHODS: Sixteen patients with HD and sixteen healthy controls completed two ToM tasks. One task involved recognising socially inappropriate behaviour and the other task required participants to judge complex mental states from photographs of people's eyes alone. To assess relationships between executive function and ToM, participants completed measures of verbal fluency, working memory and inhibition. The Problem Behaviours Assessment-short form (Neuropsychiatry Neuropsychol Behav Neurol, 14, 2001and 219) was completed twice using information from patients and their close relatives (where possible) to identify relationships between ToM impairment and behavioural problems.
RESULTS: Patients with HD made significantly more errors on ToM tasks than controls, exhibiting difficulties in judging the social appropriateness of story character's behaviour and problems inferring complex mental states from photographs of people's eyes. Patients with HD also exhibited executive dysfunction. However, there was little evidence that executive impairments were related to ToM deficits. No correlations were apparent between problem behaviours and ToM errors.
CONCLUSIONS: HD is associated with deficits in ToM. Furthermore, some of patients' ToM difficulties appear independent of executive dysfunction.