UC Davis

OBJECTIVE: To evaluate repetitive motor behaviors (RMBs) in non-autistic toddlers using direct observational methods. STUDY DESIGN: This cohort study assessed RMBs in a community sample of 679 toddlers at 24 and 36 months of age. Initial analyses examined rates of RMBs in autistic (n = 65) vs nonautistic (n = 614) participants. Subsequent analyses focused on participants without autism, first examining clinical correlates of RMBs in the full non-autistic group and then comparing rates of RMBs in 2 non-autistic subgroups: 104 participants with other developmental concerns (ODC) and 510 participants with no developmental concerns. RESULTS: A total of 36% of non-autistic children demonstrated RMB at 24 and/or 36 months of age. RMBs were significantly more likely in the ODC (55%) than the no developmental concerns (33%) group. Non-autistic participants with RMBs had significantly lower communication scores at 24 months and, at both ages, significantly higher scores on 2 measures of autism-related symptomatology than those without RMBs; however, group means fell within the average range and effect sizes were small. There were no RMB differences based on sex. CONCLUSIONS: RMBs are not uncommon in 24- to 36-month-old children who do not meet diagnostic criteria for autism. Among non-autistic children, RMBs are most likely to occur in those with other developmental challenges but are also present in some typically developing children. The presence of RMBs in toddlers should be evaluated within the context of Diagnostic and Statistical Manual of Mental Disorders, fifth edition ASD criteria, and RMBs alone without social communication challenges core to ASD should not be viewed as automatically indicative of autism.