Repetitive and Restricted Behaviours in the General Population: Validation and Heritability of Two New Instruments for Parents and Children

Background: In the autism literature repetitive and restricted behaviours (RRBs) are commonly classified into repetitive sensory-motor (RSM) and insistence on sameness (IS). These two dimensions of RRBs are believed to be relatively independent in terms of their function, as well as their neurobiological and genetic basis. As RRBs are not specific to ASD, the key for better understanding RRBs is to explore these behaviors across other neurodevelopmental and neuropsychiatric conditions, as well as their manifestation as dimensions of typical development. One of the main obstacles in conducting this type of research has been the lack of measures that allow for a detailed and systematic assessment of RRBs across the life span. Moreover, some of the most widely-used measures of RRB result in near floor-effects in unaffected siblings of ASD probands, thereby masking potentially critical information about prodromal symptoms that may portend later clinical risk.

 Objectives:

• To validate and  extend a measure of RRBs in a large, nationally representative United States sample of parents and their children
• To explore the heritability of these RRBs through parent-child intraclass correlations

Methods: Three thousand one-hundred eleven parents (31.1% male, 68.9% female; M age=38.15 years, SD= 9.95) completed the Adult Routines Inventory (ARI), a newly developed 55-item questionnaire about their own RRBs. Parents also completed the Childhood Routines Inventory-Revised (CRI-R), a 62-item questionnaire about their children’s repetitive behaviours. Children ranged in age from 1 year to 17 years, 11 months (M=9.29 years, SD= 4.82).

Results: Exploratory factor analysis (Maximum Likelihood with oblique rotation) yielded the following two factors for both the ARI and CRI-R: Rigidity/Insistence on Sameness (RIS) and Motor Stereotypies/Compulsions (MSC). Indices of skewness and kurtosis revealed normal distributions of both measures. Internal consistency and test-retest reliability for both scales for both ARI and CRI-R was excellent (Cronbach α≥ .92). The association between repetitive behaviours in children and parents was examined with the intraclass correlation coefficient (ICC). ICC for Rigidity/Insistence on Sameness was 0.73 (p< 0.0001) and for Motor Behaviours/Compulsions was 0.83 (p< 0.0001). CRI-R data were available for 844 sibling pairs (mean age= 7.99 years; SD= 4.14; 51.5% male, 48.5% female). ICC for Rigidity/Insistence on Sameness was .75 (p< 0.0001) and for Motor Behaviours/Compulsions was .85 (p< 0.00001).

Conclusions: This study introduced two RRB instruments suitable for use in both neurodevelopmental disorders and in studies of normative development, across the lifespan. We report their validity and reliability based on a large nationally-representative sample. Parent-child ICCs suggest high heritability. These measures will be useful for family studies as well as for studying children who are at risk and/or who may exhibit sub-clinical or prodromal symptoms reflecting a wide range of neurodevelopmental disorders characterized by RBBs.