Autistic Behavior

Many young children with fragile X syndrome are referred for an autism evaluation before they are ever diagnosed with fragile X due to similar early behavioral symptoms in the two disorders. Based on findings from early work in the longitudinal study, we concluded that research on the early expression of autistic features in young boys with fragile X may help distinguish between this disorder and autism. Collaboration on a study began with Dr. Gary Mesibov, an expert on autism and director of Division TEACCH, a clinical center at UNC specializing in the diagnosis and treatment of persons with autism and communication disorders.

Research Goals

Assess the extent to which autistic features were evident in a young population of boys with fragile X syndrome;
Examine the relationship between ratings of autistic behavior and developmental trajectories of young boys with fragile X syndrome; and
Compare the developmental status, functional abilities, and temperament of young boys with fragile X who did not have autism with boys with autism but no fragile X.

Methods

Participants

Boys with FXS participating in the CFXP longitudinal study in 1996-1997 were rated for signs of autistic behavior using the Childhood Autism Rating Scale (CARS) during a developmental assessment using the Battelle Developmental Inventory. A total of 57 ratings were completed on a sample of boys from 24 to 133 months of age.
A sample of 31 boys with autism who had been seen at the TEACCH clinic was recruited to participate in a one-time developmental assessment using the same measures as were used by the CFXP longitudinal study. The boys with autism were matched on chronological age, gender, and race with a sample of 31 boys from the CFXP.

Data Collection

Boys in both groups were assessed at home or school by trained evaluators.
Their parents completed questionnaires rating temperament and abilities.

Results

In the sample of boys (57) with FXS, approximately 25% scored above the cut-off for autism, suggesting a relatively high incidence of autistic behavior. All but two were in the mildly or moderately autistic range, however, and few extreme ratings were found, suggesting that severe expression of autism is a relatively rare occurrence in fragile X syndrome. No particular items on the CARS contributed disproportionately to autism ratings, and a comparison with an autistic, non-FXS sample revealed similar profiles of ratings, suggesting that differentiating fragile X and autism on the basis of CARS ratings is not possible. Chronological age and socioeconomic status did not correlate with CARS ratings, but severity of delay was strongly related, such that more severely delayed children scored higher (were more autistic) on the CARS.

Autistic behavior, as measured by the CARS, was a significant predictor of both developmental status and developmental change. Boys with autistic behavior and fragile X achieved significantly lower development and grew at significantly lower rates than those without autistic behavior. This finding was true both for overall development and development in five domains: cognitive, language, adaptive, motor and personal-social.

Children with autism exhibited a more variable profile of development in comparison with a relatively flat profile for children with FXS. Children with autism were significantly more delayed in social skills and were rated by observers as exhibiting a greater degree of impairment in cognitive, communication, and social skills. On temperament ratings, both groups were slower to adapt, less persistent, and more withdrawing than the reference group. Children with autism and FXS were substantially more delayed than children with autism or fragile X syndrome alone.