Support for a dimensional view of autism spectrum disorders in toddlers.

We examined whether clinically distinct subgroups can be derived from a sample of toddlers (n = 186) who failed the Modified Checklist for Autism in Toddlers, received a comprehensive clinical evaluation, and were diagnosed with an autism spectrum disorder (ASD). Three subgroups emerged from cluster analysis distinguished by (a) social, communication, and intellectual skills and (b) the rate and intensity of repetitive behaviors and abnormal sensory response. Preoccupations, compulsions, and rituals did not distinguish resultant subgroups. These results support a dimensional diagnostic view of ASDs in toddlers since subgroup differences were based on symptom severity rather than different symptom profiles. Results also identify specific types and levels of behavioral deficit relevant to toddler populations. Implications for early diagnosis are discussed.