Behavioral Differences Between High-Risk and Low-Risk Children with Autism

Background: Family studies indicate that the recurrence risk for Autism Spectrum Disorders (ASD) in subsequent children is approximately 10-20%, significantly higher than in the general population. There is also evidence of a broader autism phenotype of subclinical ASD symptomatology in some family members not affected with ASD. Recent studies have suggested that there may be distinct genetic mechanisms in multiplex and simplex families with ASD, which suggests the possibility of behavioral differences that result from these differing underlying mechanisms. Due to the low base rate of ASD, many current prospective studies use high-risk samples, such as younger siblings of affected children, to examine the early emergence of ASD symptomatology. However, there is little research on the degree to which high-risk samples are representative of the greater population with ASD. Few studies have looked at differences between children with ASD from multiplex and simplex families with regard to scores on the Autism Diagnostic Interview (ADI), with mixed results. The current study examines potential behavioral differences between high- and low-risk samples, with regard to severity of ASD symptoms, cognitive ability, and adaptive functioning.

Objectives: To examine behavioral differences between children with ASD from multiplex and simplex families.

Methods: Children were evaluated as a result of screening positive on an ASD screener, the M-CHAT or M-CHAT-R. ASD diagnoses were based on Autism Diagnostic Observation Schedule (ADOS) and Childhood Autism Rating Scale (CARS) scores, and clinical impression. The high-risk sample (n=31) was composed of children with ASD who had an older affected sibling, found through clinical services or research involving the older sibling. A second sample (n=31) of children diagnosed with ASD was drawn from a low-risk sample, screened at well-child pediatric visits. Groups were matched on age, gender, and maternal education. High- and low-risk sample mean scores were compared on several measures including the ADOS, CARS, Mullen Scales of Early Learning (Mullen), and Vineland Adaptive Behavior Scales-II (Vineland). T-tests were utilized to determine whether significant differences existed between groups.

Results: Samples were well matched on age (M_Low-Risk=23.52 months, SD=4.34; M_High-Risk=23.61, SD=4.23), gender, and maternal education, and did not differ significantly on ethnicity. No significant differences between the high- and low-risk children were seen with regard to severity of autism symptoms as measured by the CARS and ADOS. Similarly, no significant differences were observed on any domain of the Vineland or on the Visual Reception scale of the Mullen. However, the high-risk cases had significantly higher mean scores than the low-risk children on the Fine Motor, Expressive Language, and Receptive Language scales of the Mullen.

Conclusions: Preliminary analyses suggest that high-risk children may be somewhat higher functioning, or less developmentally delayed, than children drawn from the low-risk sample, in their language and fine motor skills, although their autism symptomatology and non-verbal cognitive abilities did not differ significantly. These results suggest that some caution may be needed in generalizing cognitive or behavioral findings from younger siblings to the larger population of children with ASD. Case ascertainment differences must be considered as possibly contributing to group differences.