Early Trajectories of Growth in Initiating Joint Attention Are Associated with ASD Severity at 36 Months

Background:  Infant-initiated joint attention (IJA) is the capacity to use gaze and gesture to share awareness of experiences or events with a social partner.  This ability typically emerges during the first year of life, and is an important precursor of later social competence.  IJA is impaired in children with Autism Spectrum Disorder (ASD) and may presage ASD symptomatology in their later-born siblings.  For example, Ibañez, Grantz, and Messinger (2012) reported that levels of IJA at 8 months in high-risk siblings (those with an older sibling diagnosed with ASD) predicted later ASD symptom severity at 30 months, but did not have a measure of symptom severity at 36 months.

Objectives:  To determine whether IJA in the first year of life predicts ASD symptom severity at 36 months in an independent sample of high-risk siblings.

Methods:   High-risk siblings (n= 42) were administered the Early Social Communication Scales (ESCS; Mundy et al., 2003) at 6 and 9 months of age.  ESCS assessments were coded for episodes of IJA (e.g., gaze from active toy to examiner), and the total number of IJA episodes was divided by the length of the ESCS to create rates per minute.  The Autism Diagnostic Observation Schedule (ADOS) was administered at 36 months.  Calibrated ASD severity scores were calculated for each child to provide a continuous measure of ASD symptomatology (Gotham, Pickles, & Lord, 2009).  Clinical best estimate diagnosis was given at 36 months by a licensed clinical psychologist.

Results:   Hierarchical linear modeling was used to examine initial levels and growth in IJA from 6 to 9 months in high-risk siblings and to examine associations with ASD diagnosis and severity.  Growth in IJA was significant between 6 and 9 months, β₁₀ = 0.96, t(28) = 3.69, p = .001.  Growth did not differ by diagnostic outcome (ASD [n=8] or no ASD [n=23]), β₁₁ = -0.76, t(28) = -2.01, p = .054.  By contrast, growth in IJA from 6 to 9 months was associated with ASD severity at 36 months, with lower rates of growth associated with higher ASD severity scores, β₁₁ = -0.14, t(28) = -2.84, p =.009.  Correlations, which provide an effect size, confirmed that estimates of slope, r(30) = -.47, p = .01, as well as 9 month levels of IJA, r(28) = -.43, p=.02, were associated with ASD severity.

Conclusions:    The rate of high-risk siblings’ growth in IJA from 6 to 9 months was negatively associated with later ASD symptomatology at 36 months.  Early upward trajectories of IJA growth—in the period when infants develop referential communication—appear to be relatively sensitive predictors of symptom level—although not diagnosis—in high-risk siblings. As in Ibañez et al., levels of IJA before 12 months were predictive of three year ASD symptomatology. In both studies, IJA was elicited in the ESCS, a routine, standardized, semi-structured task with an examiner.  The current study shows in a second, independent sample that high-risk infants’ early ability to share an experience with a social partner is associated with later ASD symptomatology.