Using longitudinal data from brief observations, we were able to find stable diagnostic differences in both prevalence
of RRBs measured during the ADOS among 655 observations of children (from 455 toddlers and preschoolers ranging from 8 to 56 months of age) with autism, PDD-NOS, NS and TD. The diagnostic differences in RRBs found in the current study suggest the importance of RRBs to early diagnosis of ASD, in line with previous studies that have shown similar results using parental interviews and questionnaires (Watson et al., 2007
, Richler et al. 2007
; Lord et al, 2006
). The results of this study also extend the findings of Morgan, Wetherby & Barber (2008)
who reported diagnostic differences in RRBs among children with ASD, developmental delays, and typical development from 18 to 24 months based on systematic observations.
The present study adds to the growing body of literature showing that semi-structured observations which occur in a brief time period can successfully provide an opportunity for the assessment of RRBs. In fact, the diagnostic differences in RRBs found in the present study using the ADOS highlight the importance of using observational data with very young children because of evidence that parents may not notice RRBs in very young children (Chawarska, Klin, Paul, & Volkmar, 2007
). While parents might have more opportunities to observe RRBs in their children, they may also have more difficulties in judging the abnormality of such behaviors compared to clinicians. In fact, though our results indicated that most children with ASD showed RRBs during the ADOS, the prevalence analyses revealed that there were 11 cases in the PDD-NOS group who scored 0 on the RRB totals in the ADOS. However, it was found that all children with autism and
those with PDD-NOS had at least one RRB at the time of assessment when RRB scores from both the ADI-R and ADOS, which were administered within the same week, were taken into account. All of the children with ASD who scored 0 on the RRB totals in the ADOS scored more than 0 on at least one of the current
RRB item in the ADI-R.
Importantly, our findings with very young children suggest that when data from observations and parent interviews are combined, RRBs are almost always present in ASD, including in children given PDD-NOS diagnoses. This supports the idea of having RRBs as a requirement for the diagnosis of broader ASD (including PDD-NOS) in new diagnostic frameworks under development when information from parent report and observation are both taken into account.
The results of the present study on the differences in the prevalence
of RRBs between the ASD (autism and PDD-NOS) and NS groups are of practical significance. Even though RRBs in the ASD groups were consistently more prevalent and higher in severity than the NS and TD groups consistent with past studies (Bodfish, Symons, Parker, & Lewis, 2000; Watson et al., 2007
; Richler et al., 2007
), RRBs were relatively common in the NS group. On average, children with NS showed at least one type of RRBs during an ADOS session while ASD groups showed 2–3 types of RRBs on average. Although current diagnostic guidelines, such as DSM-IV (APA, 1994
), require the presence of a single RRB for a diagnosis of ASD, clinicians should be aware that the presence of any single RRB alone does not distinguish children with ASD from those with other non-spectrum disorders. Nevertheless, though the appearance of RRBs is not unique to ASD, particularly in very young children, the presence of a RRB coupled with social and communication deficits increases the likelihood of a stable diagnosis of ASD over years to come (Lord et al., 2006
In the present study, the likelihood of having an RRB was the same for both autism and PDD-NOS groups; though the rated severity of these RRBs was higher in children over age two with autism than PDD-NOS diagnoses. This is consistent with the past literature that has shown that no single behavior or factor differentiated PDD-NOS from autism or Asperger’s syndrome (Klin et al., 2005
). This is also in line with previous research using the ADI-R indicating that individuals with autism had significantly higher scores than those with PDD-NOS in the repetitive sensory-motor behaviors
factor (Georgiades et al. 2007
). These findings support the concept of a single category ASD differentiated by severity, rather than separate subgroups of ASD such as PDD-NOS or autism..
Consistent with previous findings on the trajectory of RRBs (Richler et al., 2010
), the severity of RRBs was independent of age such that the RRB totals were stable over time in both ASD and NS groups. Even though these results were expected because ADOS items were originally selected to be differentially diagnostic at different language levels and ages, it is interesting that RRB totals for typically developing children were still associated with age such that their scores decreased over time, showing that differentiating children with ASD from typically developing children becomes easier as they get older. Early RRB scores in children with ASD and NS under 30 months predicted their later RRB scores indicating that RRBs that are severe in toddler years often remain severe over the course of development into preschool years.
The current study showed that IQ is more closely related to the manifestation of RRBs in older children with PDD-NOS, NS and TD than very young or more severely affected children. Lower NVIQ scores were not associated with higher RRB scores in children with autism (regardless of their age) and children under 25 months (regardless of their diagnosis). This might be because of differences in the NVIQ distributions by cohort. In the present study, the older cohorts had the fewer children with lower NVIQ scores than younger cohorts which might have minimized the effect of NVIQ scores on RRB totals for younger cohorts. However, another possibility is that older children with higher IQs may have more interests and abilities that foster participation in less repetitive activities based on similar findings by Bishop et al. (2007). In toddler years, these options may be limited since these very young children have not yet acquired the chance to develop creative play and more productive activities regardless of the level of their cognitive functioning. As children enter preschool years, they would be more likely to be exposed to novel environments and activities that would facilitate the development of more elaborate play. In the same way, since children with autism have more severe levels of impairment in their social and communication functioning compared to those with PDD-NOS, a milder form of ASD, they may have fewer opportunities to develop more productive, non-repetitive activities through social interactions. These findings have important implications for treatment. One of the goals of early intervention may be to alter the course of developmental trajectories of RRBs by providing alternative behaviors that are equally motivating.
As we hypothesized, different patterns of association between the prevalence of RRBs and child characteristics were observed. Interestingly, three items, sensory interests, hand and finger mannerisms,
and complex mannerisms
showed similar patterns of associations with NVIQ, age, and diagnosis, distinct from the other RRB items. Surprisingly, the prevalence of these three items was associated with NVIQ but was stable over time, which is similar to findings from parent reports on repetitive sensory-motor behaviors
(RSMB) in past studies (Richler et al., 2010
; Hus et al., 2007; Lam, Bodfish, & Piven, 2008
). Turner (1999)
described RSMBs as “low-order” behaviors related to developmental delays, which was also true for these three items that were more prevalent in children with lower NVIQ scores. Other items, stereotyped language, intonation of vocalizations
, and repetitive behaviors
differed in terms of their associations with NVIQ, age, diagnosis, and gender. Repetitive behaviors
and intonation of vocalizations
were independent of NVIQ, and stereotyped language
and repetitive behaviors
became more prevalent with increasing age, which suggests that these items in the ADOS might capture more “higher-order” behaviors (Turner, 1999
). This can be because, unlike in the ADI-R and more advanced Modules of the ADOS where the item, repetitive behaviors
, is distinguished from compulsions
, repetitive behaviors
in the earlier Modules of the ADOS encompass a very broad range of behaviors including both Repetitive Sensory-Motor and Insistence of Sameness
behaviors (e.g. repetitive nonfunctional use of toys; insistence on unusual routines). These results support the idea of different classes of RRBs and heterogeneity among different types of RRBs in associations with intellectual abilities and age (Turner, 1999
). The results also support that examining RRB subtypes and their relationships with other characteristics (e.g. NVIQ, age, gender, etc) can help us to better identify specific types of RRBs predictive of diagnosis. Stereotyped language
did not differentiate between diagnostic groups likely because of the still limited language levels of the children with ASD. A main effect of gender emerged for repetitive behaviors.
However, since there was no significant effects of gender on NVIQ scores and on the other RRB subtypes as well as on the RRB total scores, the possibility of gender differences in subtypes of RRBs needs further exploration in future studies.
The present study assessed children with TD only up to 30 months in comparison to the other groups of children who were assessed up to 56 months. Had the TD group been followed at older ages, we would have been able to compare the rest of the groups to the TD group from age 31 to 56 months. Furthermore, children in the present study were divided into 6 cohorts, and the time interval for each cohort was about 5 months. Since rapid developmental changes occur during toddler and preschool years, it will be important for further studies to examine RRBs in those early years with shorter time intervals such as 1 or to 2 months to capture the rapid developmental changes in more detail.
One other limitation was that, in order to maintain a sufficiently large sample, we combined samples who received two different algorithms even though there was a slight difference in the composition of the RRB totals between these two algorithms (intonation of vocalizations was substituted for stereotyped language for the no words algorithm). In addition, one could argue that the language items can be considered not as central as the other items to the concept of RRBs. To address these concerns, we performed the same set of analyses using the raw RRB totals without language items for the severity of RRBs. However, when the raw totals were used, all of the results remained the same although the differences in the RRB raw totals between subgroups of ASD were not significant anymore. This confirms our belief that RRB algorithm totals can validly represent the severity of RRBs to test our hypotheses. On the other hand, it will be interesting for the future research to examine nonverbal and verbal samples separately if possible to investigate the role of the child’s verbal level on RRBs in regards to items related to language.
Furthermore, not all aspects of RRBs can be assessed in brief observations. Distinctions between insistence on sameness and other RRBs was not possible in these young because frequency, content or quality of a behavior were not coded sufficiently specifically. Parent and other caregiver (e.g. teacher; therapist) reports remain critical in order to capture broader aspects of RRBs. Semi-structured observations with very young children suspected of having ASDs can provide more information than even we originally assumed, but still must be complemented by detailed information from people who know them well.
This heterogeneity in RRBs found even in these very young children during relatively brief observations in the current study is consistent with past studies based on parent interview, suggesting researchers should attend to emerging differences among RRB items that could easily be missed by grouping multiple items under one single domain (Lam, Bodfish, & Piven, 2008
; Cuccaro et al, 2003
; Szatmari et al., 2006
; South et al, 2005
). Further evidence about the heterogeneity in RRBs and their developmental trajectories may hold important clues for etiology, pathological mechanisms and treatment of RRBs.