Are the three domains of autism spectrum disorders (social interaction, communication, and stereotypies and rigidity) clustering together in the general population at 18 months?

Background:   ASD are defined by deficits in social interaction and communication, and by stereotyped behaviour. It is unclear whether these three domains correlate in the general population at young age, and cluster together at the level of the individual.

Objectives: Insight into the underlying structure of ASD-symptoms in the general population may facilitate the development of screening-instruments and screening-procedures.

Methods: Data have been collected in the context of the ongoing prospective Autism-Birth-Cohort-Study, funded by the Norwegian Institute of Public Health, and National Institute of Health of the USA. Mothers of 13,346 18-months-old children completed a questionnaire including items about their child’s socio-emotional development and behaviour. The DSM-IV three-domain classification of ASD at 18 months was tested using exploratory and confirmatory factor analyses. Latent Class Analysis (LCA) was conducted to empirically identify homogeneous groups of children.

Results: An exploratory factor analysis extracted a three-factor solution with a satisfactory fit and meaningful interpretation. Confirmatory factor analysis demonstrated further support for this three-factor structure. LCA revealed four 4 classes. Class 1 (0.7% of  sample) has the highest scores of all classes on the domains of Social interaction and Communication, but moderate scores on the domain Stereotypies; Class 2 (18.6% of sample) scores in-between class 1 and 4 on Social interaction and Communication but scores low on Stereotypies; Class 3 (13.4%) scores low on the domains of Social interaction and Communication, but the highest of all classes on the domain of Stereotypies; Class 4 (67.4% of sample) represents the reference group which relatively low scores on all domains.

Conclusions: The underlying structure of ASD symptoms is generalizable to the population at 18 months. In the general population four classes can be identified with a clear distinction between the clusters Social interaction and Communication on one hand and the cluster Stereotypies on the other hand.