Executive function and theory of mind performance of boys with fragile-X syndrome

Fragile-X syndrome is the most common genetically inherited cause of intellectual disability. People with this syndrome typically show a behavioural profile of abnormal social interactions which are similar in some ways to those seen in people with autism. The present study investigated whether cognitive processes which have been hypothesized to underlie social abnormalities associated with autism are also impaired in boys with fragile-X syndrome without autistic spectrum disorders. Eight boys with fragile-X syndrome and eight with intellectual disability of unknown aetiology, matched on receptive verbal ability, age and with no diagnosis of autism, were tested on a battery of theory of mind and executive function tasks. Significantly more boys with fragile-X syndrome failed the simplest theory of mind task. However, this could be attributed to overall level of ability rather than group membership. No differences were found between the groups on any other measures used. A proportion of both groups failed first- and second-order false belief tasks. The performance of both groups on the executive function measure was at the floor of the test. At low levels of overall ability, the performance of boys with fragile-X syndrome and boys with intellectual disability of unknown aetiology may be more similar than they are different The implication of this result for clinical interventions is discussed.