Differrential Early Temperament Trajectories in Children at High Risk of Developing Autistic Spectrum Disorder

Background: The heterogeneous nature of Autistic Spectrum Disorder (ASD) has posed an ongoing challenge for attempts aimed at identifying core neuropathological mechanisms. To date, limited progress has been made in identifying subgroups that are reliably distinguished by course of the disorder, response to treatment or prognosis/outcome. One promising approach to understanding the heterogeneity in ASD is the study of temperament. Individual differences in temperament have been documented in samples of children with ASD (Sutton et al., 2003), and in high-risk 2-year-olds subsequently diagnosed with ASD (Garon et al., 2008). 

Objectives:

The main objective of the present study was to determine whether differences in clinical course (as indexed by age of onset and severity of symptoms) are associated with distinct early temperament trajectories.

Methods:

Infant siblings of children with ASD were assessed prospectively at 6 and 12 months on the Infant Behavior Questionnaire (IBQ) and at 24 months on the Toddler Behavior Assessment Questionnaire (TBAQ), both completed by parents. At 36 months, an independent ‘gold-standard’ diagnostic assessment for ASD was conducted. Two temperament factors, reactivity to the environment and distress, found previously to be associated with ASD (Garon et al., 2008) were used in the present analysis. Scores on these temperament factors were analyzed using a linear mixed model with age (6, 12 and 24 months) and subgroups (defined by onset and severity of ASD symptoms) as the independent variables.  

Results:

Three distinct early temperament trajectories distinguished subgroups within the high-risk infant sibling cohort. Among those diagnosed with ASD, children with earlier and more severe symptoms were distinguished by a profile of strikingly low reactivity to the environment from 6 months of age onward coupled with a dramatic increase in distress between 6 and 24 months. While their temperament was more stable over time, children with later and less severe symptoms were distinguished by a profile of high distress from 6 months of age onward coupled with a gradual decrease in reactivity to the environment between 6 and 24 months. Children in the sib group who were not diagnosed with ASD had higher than normal reactivity from 6 months of age onward combined with higher than normal distress from 12 months onward. Finally, at 12 months, even after co-varying ASD symptoms, children in the sib group who were low on both environmental reactivity and distress (flat affect) at 12 months experienced the largest decrement in IQ between the ages of 12 and 24 months.

Conclusions:

The present findings suggest that early temperament trajectories may provide insights into the heterogeneity of ASD beyond that provided by traditional diagnostic approaches.