Theory of mind impairment in adult-onset myotonic dystrophy type 1

Patients with myotonic dystrophy type 1 (DM 1) exhibit behavioral disorders and distinctive personality traits. We hypothesize that this is due to altered social cognitive function. To investigate the cognitive basis of this impairment in DM 1 patients, we examined their theory of mind (ToM) ability, which is the specific cognitive ability to understand the mental states of others. Nine adult-onset DM 1 patients (4 men and 5 women) performed 2 ToM tasks: "Reading the Mind in the Eyes" test and faux pas recognition test. DM 1 patients were found to be impaired in both ToM tests, but had no difficulty with control tasks designed to test visual and lexical comprehension. The present results indicate that social cognitive impairment in patients with adult-onset DM 1 is associated with ToM dysfunction, which could be due to the brain lesions associated with this disease.