Regulation of Activity Level and Affective Responses in Toddlers with ASD

Background: Atypical temperamental characteristics are commonly seen in people with ASD: adults and older children with ASD have highly comorbid disorders including anxiety, ADHD, mood disorder, or behavioral problems (Simonoff et al, 2008), and parents frequently recall atypical temperament and behavior in early development, with 30-50% recalling abnormalities within the first year (Zwaigenbaum et al, 2005).  Despite these findings, little research has explored the relationship between temperamental phenotypes and the core symptoms of ASD. 

Objectives: 1) To compare the frequency of atypical behavioral and emotional reactivity in toddlers diagnosed with AUT, PDD, and DD, and to examine if any temperamental characteristics are associated with AUT in particular.  2) To assess the relationship of temperament to the symptoms and severity of ASD. 3) To explore if such characteristics are identifiable in early infancy in a sample of 12-month-olds later diagnosed with ASD. 

Methods: Two samples were considered: (1) clinic-referred 18-36 month-olds with autism (AUT, n=180), PDD-NOS (n=68), and non-ASD developmental delays (DD, n=83), and (2) 12-month-old infants at high- and low-risk for ASD, later diagnosed with ASD (n= 12), with atypical features and delays (ATYP, n=34), and as typically developing (TYP, n=37).  Subjects were assessed using the Mullen Scales of Early Learning (Mullen) and Autism Diagnostic Observation Schedule (ADOS-G: Toddlers, ADOS-T: Infants), and by a parent interview (Vineland-II).  Behavioral and emotional reactivity were quantified based on three summary items: Range of Affective Expressions (Items B3/B4), Overactivity (Item E1), and Anxiety (Items E3/E4) of ADOS-G and T, respectively. The items were recoded into 0/1 categories with 0 denoting no atypical features, and 1 capturing presence of abnormalities in the area. 

Results: The toddlers with AUT were significantly more behaviorally active (Χ²(2)=20.12,p=.001) and exhibited more restricted range of affective expressions (Χ²(2)=73.75,p=.001) during the ADOS-G, while no significant differences in anxiety were found.  After controlling for nonverbal DQ in toddlers with ASD (autism and PDD-NOS combined), higher activity levels were positively associated with autism severity scores (p=.035).  Toddlers with a more restricted range of affective expressions had higher autism severity scores (p=.001), lower verbal DQ (p=.001) and poorer adaptive communication skills (p=.001).  However, higher level of anxious apprehension, was associated with higher verbal DQ (p=.002) and adaptive communication scores (p=.042). The 12-month-olds later diagnosed with ASD similarly exhibited high activity levels (Χ²(2)=11.1,p=.004) and more limited affective expressions (Χ²(2)=27.14,p=.001).  In contrast to the toddlers, these infants also exhibited significantly lower levels of anxiety than their typically developing peers (Χ²(2)=5.75,p=.056). 

Conclusions: Toddlers with autism exhibit marked difficulties in regulating their activity level and affective responses. These difficulties are apparent even in 12-month-olds who are later diagnosed with ASD.  Regardless of the level of cognitive functioning, high activity level and restricted affective range were associated with more severe symptoms of autism and lower verbal communication. However, more anxious toddlers tended to have higher levels of verbal ability.  The results suggest that the temperamental dimensions associated with regulation of activity level and affective responses are linked with the early syndrome expression and represent potentially important area for investigation.