Family history data on 99 autistic and 36 Down's syndrome probands are reported. They confirmed a raised familial loading for both autism and more broadly defined pervasive developmental disorders in siblings (2.9% and 2.9%, respectively, vs 0% in the Down's group) and also evidence for the familial aggregation of a lesser variant of autism, comprising more subtle communication/social impairments or stereotypic behaviours, but not mental retardation alone. Between 12.4 and 20.4% of the autism siblings and 1.6% and 3.2% of the Down's siblings exhibited this lesser variant, depending on the stringency of its definition. Amongst autistic probands with speech, various features of their disorder (increased number of autistic symptoms; reduced verbal and performance ability) as well as a history of obstetric complications, indexed an elevation in familial loading. No such association was seen in the probands without speech, even though familial loading for the lesser variant in this subgroup, was significantly higher than in the Down's controls. The findings suggest that the autism phenotype extends beyond autism as traditionally diagnosed; that aetiology involves several genes; that autism is genetically heterogeneous; and that obstetric abnormalities in autistic subjects may derive from abnormality in the foetus.

The development of a new standardized investigator-based interview for use in the differential diagnosis of pervasive developmental disorders is described, together with a diagnostic algorithm (using ICD-10 criteria) based on its use. Good interrater reliability for algorithm items was shown between four raters, two in Canada and two in the UK, who rated 32 videotaped interviews. The items also significantly discriminated between 16 autistic and 16 nonautistic mentally handicapped subjects. The algorithm based on ICD-10 identified all 16 autistic individuals and none of the 16 nonautistic subjects.

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High-functioning autistic adults were compared with normal adults using a battery of tests devised to assess the recognition and expression of emotional cues in both facial and vocal modalities. The autistic subjects were relatively impaired in both the appreciation and production of emotional expressions. Although no one test provided a clear-cut separation of the groups at the individual level, composite scores did separate the groups quite well. It is suggested that this battery of tasks may have some value in family genetic studies of autism that need to identify subclinical deficits that might be aetiologically linked with autism.

Although a number of advanced theory of mind tasks have been developed, there is sparse information on whether performance on different tasks is associated. The study examined the performance of 20 high-functioning 6- to 12-year-old children with autism spectrum disorder and 20 controls on three high-level theory of mind tasks: Strange Stories, Cartoons and the children's version of the Eyes task. The pattern of findings suggests that the three tasks may share differing, non-specific, information-processing requirements in addition to tapping any putative mentalizing ability. They may also indicate a degree of dissociation between social-cognitive and social-perceptual or affective components of the mentalizing system.