Restricted and Repetitve Behaviors (RRBs) in Simplex and Multiplex ASD

Background: Limited research has been conducted to explore the extent to which affected infant siblings of children with ASD are representative of the general population of children with ASD. Previous research from our lab suggests that affected infant siblings in multiplex families may be higher functioning than children with ASD in simplex families with respect to language and cognitive ability. While overall ASD severity did not differ, prior analyses suggested that children with ASD from multiplex families might display more restricted and repetitive behaviors (RRBs) than those from simplex families. The current study proposes to further explore the profile of RRBs in simplex and multiplex ASD using a four-factor model.

Objectives: To examine differences in RRBs in toddlers with ASD from simplex and multiplex families.

Methods: A sample of 39 younger siblings with ASD (M_age = 24.2 months) from multiplex families (M-ASD) was compared to a matched sample of 39 children with ASD (M_age = 24.4 months) from simplex families (S-ASD). Samples were matched pairwise on age, gender, maternal education, and ethnicity. Presence and type of RRBs was assessed using parent report (ADI/parent interview) and clinician-rated measures (CARS, ADOS, and DSM-IV-TR). Based on previous research on the ADI, RRBs were divided into three factors - Insistence on Sameness (IS), Restricted Motor Behaviors (RMBs), and Circumscribed Interests (CI). A fourth factor, Unusual Sensory Responses (SE), was added. All RRB items were coded as present or absent. RRB factor scores and an ADI RRB total score were calculated and compared between groups. Relevant CARS items, ADOS items, and DSM-IV-TR criteria were selected based on these factors and compared between groups.

Results: Samples were well matched on age, gender, maternal education, and ethnicity (p’s > .5). Based on parent-report, the M-ASD group exhibited more RRBs than the S-ASD group (p = .01, d = .76). Significant differences between M-ASD and S-ASD groups were observed in the Insistence on Sameness (p =.045, r = .25) and Unusual Sensory Responses (p =.039, r = .28) factors. More parents of M-ASD children endorsed the ADI Compulsions/Rituals item (M-ASD 29% vs. S-ASD 11%) and ADI Unusual Sensory Interests item (M-ASD 69% vs. S-ASD 27%) than parents of S-ASD children. Similarly, more M-ASD children meet DSM-IV-TR diagnostic criteria for adherence to routines than S-ASD children (M-ASD 26% vs. S-ASD 11%). No significant differences were observed on clinician-rated measures of behavior (ADOS and CARS).  

Conclusions: Based on parent report, M-ASD children display more RRBs than S-ASD children, specifically in the areas of Insistence on Sameness and Unusual Sensory Responses. Scores on clinician-rated measures failed to corroborate these findings, potentially due to the small window in which a child is observed during an evaluation. This study builds upon previous research suggesting the heterogeneity of RRB presentation within the ASD population. Further research is needed to determine whether the presence of an older sibling with ASD sensitizes parents to the presence of RRBs and leads to more accurate reporting or perhaps even an over-reporting of symptoms.