Background. There is substantial evidence that the genetic liability to autism confers a risk for a range of more subtle social and communication impairments, as well as stereotyped and repetitive behaviours. Recent research suggests that increased expression of particular personality traits may be a manifestation of the liability to autism.

Methods. To investigate this we examined the personality traits of the adult relatives of 99 autistic and 36 Down's syndrome probands, using the informant version of the Modified Personality Assessment Schedule.

Results. There was significantly increased expression of the traits anxious, impulsive, aloof, shy, over-sensitive, irritable and eccentric among the autism relatives with evidence of different profiles for male and female relatives and for parents and adult children. Factor analysis revealed three broad groups of traits, two of which (‘withdrawn’ and ‘difficult’) appeared to reflect impairments in social functioning and a third group of anxiety related traits (‘tense’). Each of these factors differed in their pattern of associations with the factor we termed ‘withdrawn’ showing a similar pattern of association to that found for other autism related conditions. The ‘tense’ factor appeared in part to be related to the burden of caring for an autistic child.

Conclusions. This study confirms the finding that particular personality traits may aggregate in the family members of autistic individuals and furthermore that some of these traits may be a manifestation of the liability to autism.