To our knowledge, no prospective studies of the developmental course of early and later diagnosis of autism spectrum disorders from 14 months of age exist.Objective: To examine patterns of development from 14 to 24 months in children with early and later diagnosis of autism spectrum disorders.Design: Prospective, longitudinal design in which 125 infants at high and low risk for autism were tested from age 14 to 36 months. Comprehensive standardized assessments included measures of social, communication, and play behavior.Setting: Testing occurred at a major medical and research institution as part of a large, ongoing longitudinal study.Participants: Low-risk controls (n=18) and siblings of children with autism, grouped on the basis of outcome diagnostic classification at 30 or 36 months: autism spec-trum disorders (early diagnosis, n=16; later diagnosis, n = 14), broader autism phenotype (n = 19), and nonbroader autism phenotype (n=58).Main Outcome Measures: Social, communication, and symbolic abilities were assessed.Results: Social, communication, and play behavior in the early-diagnosis group differed from that in all other groups by 14 months of age. By 24 months, the later-diagnosis group differed from the non-autism spectrum disorder groups in social and communication behavior, but not from the early-diagnosis group. Examination of growth trajectories suggests that autism may involve developmental arrest, slowing, or even regression. Conclusion:This study provides insight into different patterns of development of children with early vs later diagnosis of autism spectrum disorders.

Background Social and communication impairments are core deficits and prognostic indicators of autism. We evaluated the impact of supplementing a comprehensive intervention with a curriculum targeting socially synchronous behavior on social outcomes of toddlers with autism spectrum disorders (ASD). Methods Fifty toddlers with ASD, ages 21 to 33 months, were randomized to one of two 6-month interventions: Interpersonal Synchrony or Non-Interpersonal Synchrony. The interventions provided identical intensity (10 hours per week in classroom), student-to-teacher ratio, schedule, home-based parent training (1.5 hours per month), parent education (38 hours), and instructional strategies, except the Interpersonal Synchrony condition provided a supplementary curriculum targeting socially engaged imitation, joint attention, and affect sharing; measures of these were primary outcomes. Assessments were conducted pre-intervention, immediately post-intervention, and, to assess maintenance, at six-month follow-up. Random effects models were used to examine differences between groups over time. Secondary analyses examined gains in expressive language and nonverbal cognition, and time effects during the intervention and follow-up periods. Results A significant treatment effect was found for socially engaged imitation (p=0.02), with more than doubling (17% to 42%) of imitated acts paired with eye contact in the Interpersonal Synchrony group after the intervention. This skill was generalized to unfamiliar contexts and maintained through follow-up. Similar gains were observed for initiation of joint attention and shared positive affect, but between-group differences did not reach statistical significance. A significant time effect was found for all outcomes (p<0.001); greatest change occurred during the intervention period, particularly in the Interpersonal Synchrony group. Conclusions This is the first ASD randomized trial involving toddlers to identify an active ingredient for enhancing socially engaged imitation. Adding social engagement targets to intervention improves short-term outcome at no additional cost to the intervention. The social, language, and cognitive gains in our participants provide evidence for plasticity of these developmental systems in toddlers with ASD. http://www.clinicaltrials.gov/ct2/show/NCT00106210?term=landa&rank=3

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