This study was designed to explore the behavioral phenotype of autism in a group of young children with fragile X syndrome (FXS). Twenty-four children with FXS, ages 21 to 48 months, were compared with two well-matched groups: 27 children with autism (AD) and 23 children with other developmental delays (DD), on two standardized autism instruments, as well as on measures of development and adaptive behavior. Two FXS subgroups emerged. One subgroup (n = 16) did not meet study criteria for autism. Their profiles on the autism instruments and the developmental instruments were virtually identical to the other DD group. The other FXS subgroup (n = 8, or 33% of the total FXS group) met study criteria for autism. Their profiles on the autism instruments were virtually identical to the group with autism. The finding of two FXS subgroups raises a hypothesis of additional genetic influences in the FXS autism group, warranting further genetic studies.

Simple imitation skills were differentially impaired in young children with autism, and lack of social cooperation did not account for their poor performance. In autism, imitation skills clustered with dyadic and triadic social interactions and overall developmental level, but were not related to play or language development. For comparison children, all these areas were inter-related. Hypotheses about a specific dyspraxic deficit underlying the imitation performance in autism were not supported.

The Short Sensory Profile was used to assess parental report of sensory reactivity across four groups of young children (n = 102). Groups were autism (n = 26), fragile X syndrome (n = 20), developmental disabilities of mixed etiology (n = 32), and typically developing children (n = 24). Groups were comparable on overall mental age (x = 22 months), and clinical groups were comparable on chronological age (x = 31 months). Significant differences were detected at alpha <.01 for tactile sensitivity [F(3,99) = 10.01], taste/smell sensitivity [F(3,99) = 11.63], underreactive/seeks stimulation [F(3,99) = 4.56], auditory filtering [F(3,99) = 19.67], and low energy/weak muscles [F(3,99) = 14.21]. Both children with fragile X syndrome and children with autism had significantly more sensory symptoms overall than the two comparison groups, and children with autism did not differ significantly from children with fragile X syndrome. Both groups were more impaired than developmentally delayed and typically developing children in tactile sensitivity and auditory filtering. Children with autism were more abnormal in responses to taste and smell than all other groups. Children with fragile X syndrome were more abnormal than all other groups in low energy/weak muscles. Sensory reactivity of children with developmental delays was comparable to mental age-matched typically developing toddlers. Correlational analyses indicated that neither overall developmental level nor IQ was related to abnormal sensory reactivity in children with autism or general developmental disorders. However, abnormal sensory reactivity had a significant relationship with overall adaptive behavior.

The executive dysfunction hypothesis of autism has received support from most studies of older people with autism; however, studies of young children have produced mixed results. Two studies are presented that compare the performance of preschoolers with autism (mean = 51 months/4.3 years of age) to a control group matched on age, and verbal and nonverbal ability. The first study (n = 18 autism and 17 control) found no group differences in performance on 8 executive function tasks (A not B, Object Retrieval, A not B with Invisible Displacement, 3-Boxes Stationary and Scrambled, 6-Boxes Stationary and Scrambled, and Spatial Reversal), but did find that children with autism initiated fewer joint attention and social interaction behaviors. The second (longitudinal) study of a subset of the children (n = 13 autism and 11 control) from the first study found that neither groups' performance on Spatial Reversal changed significantly over the course of a year. The results of these studies pose a serious challenge to the executive dysfunction hypothesis of autism.

A framework for examining developmental changes in romantic relationships is presented. The chapter describes research illustrating these developmental differences and delineates an agenda for subsequent developmental work.

Twenty six children with autism, 24 children with developmental disabilities, and 15 typically developing children participated in tasks in which an adult displayed emotions. Child focus of attention, change in facial tone (i.e., hedonic tone), and latency to changes in tone were measured and summary scores of emotional contagion were created. Group differences existed in the ratio of episodes that resulted in emotional contagion. Correlations existed between measures of emotional contagion, measures of joint attention, and indices of severity of autism. Children with autism demonstrated muted changes in affect, but these responses occurred much less frequently than in comparison groups. The findings suggest directions for early identification and early treatment of autism.

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