Context: 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 spectrum disorders (early diagnosis, n = 16; later diagnosis, n = 14), broader autism phenotype (n = 19), and non-broader 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.