Social visual engagement — visual attentiveness and engagement with social cues — is one of the earliest observable actions of infants and plays an important role in how infants learn to socially interact with others. Children with ASD frequently display impairment of social visual engagement, a deficit that can be detected as early as the first six months of life. There is evidence that ASD is heritable, but the mechanisms of genetic influence on development and behaviors are not well understood. To better understand the social development of children with ASD, it is important to investigate the genetic factors that influence social visual engagement.

In this study, researchers performed eye-tracking experiments on a group of 338 toddlers, consisting of 82 identical twins, 84 fraternal twins, 88 non-twins with ASD, and 84 non-related controls. By comparing groups of toddlers 18-24 months of age who were either genetically identical (identical twins), genetically similar (fraternal twins), or genetically unrelated (non-related controls and non-related children with ASD), the researchers were able to investigate whether responses to social cues are genetically determined. They did so by measuring patterns of the toddlers’ visual responses to videos that mimic typical social situations.

First, the researchers presented the videos to identical twins, fraternal twins, and non-related controls. As the toddlers watched the social interactions presented in the video, specialized equipment tracked their eye movements. The researchers used these measurements to track the speed with which toddlers looked toward faces and the amount of time the toddlers gazed at the eye and mouth regions, specifically to determine concordance— the probability that the two individuals share a trait or characteristic. They found that identical twins had the greatest concordance of their visual responses to both eye and mouth stimuli: 91% of the time, they responded similarly to each other when observing eye stimuli, and 86% of the time when observing mouth stimuli. Fraternal twins showed modest concordance with 35% concordance for eye and 44% concordance for mouth stimuli, and non-related controls showed no concordance in their visual responses. Since identical twins are more genetically similar than fraternal twins, a higher level of concordance in identical twins indicates that visual engagement is highly heritable.

Identical twins also showed greater concordance in the amount of time spent looking at facial features than they did in the amount of time spent looking at other non-social objects in the videos. Fraternal twins and non-related controls did not show a significant difference in concordance when looking at social versus non-social aspects of the videos.

Next, the researchers looked at the timing and direction of eye movements of the three groups. Identical twins were more likely to move their eyes at the same time in response to social stimuli than fraternal twins or non-siblings. Further, identical twins were more likely to move their eyes in the same general direction than were fraternal twins. The researchers also considered timing and direction together and found that identical twins were more likely than fraternal twins to look in the same direction at the same time. Together, these results indicate that the level of concordance of responses to social visual stimuli was highest for the genetically identical toddlers, suggesting that social visual engagement is linked to genetic factors.

Lastly, the researchers compared visual responses of typically developing identical twins, fraternal twins, and non-siblings with those of toddlers with ASD. They found that the toddlers with ASD showed reduced responses to the social aspects of the videos. Based on their findings that social visual engagement is genetically determined, they suggest that genetic differences in children with ASD underlie their differences in social behavior compared to their typically-developing peers.

The severity of ASD is highly variable, and currently, little is known about the relationship between symptoms that present early in life and long-term outcomes. Intellectual ability, typically assessed by intelligence quotient (IQ), can serve as a strong outcome predictor for children with and without ASD. Although recent literature has investigated the relationship between ASD and IQ, no studies have identified the different ways IQ can change over the course of a child’s development, nor how these trajectories affect ASD outcomes.

In this study, researchers presented four hypotheses related to intellectual ability and ASD outcomes, hypothesizing that: 1) their findings would support previous research, which suggests that there are four different IQ trajectories for children with ASD from two to eight years old; 2) only the small proportion of children who lose their ASD diagnoses by eight years old would be more likely to have higher IQs at two years old, while IQ would not be significantly related to ASD symptom severity in children who don’t lose their diagnoses; 3) children who had the greatest increases in IQ would have relatively higher non-verbal abilities at age 2 and show strong adaptive communication development from age 2 to 8; and 4) children who showed increases in IQ would demonstrate low levels of internalizing behaviors, such as anxiety, depression, and complaints of physical ailments.

To test these hypotheses, the researchers tracked changes in intellectual ability for 102 children with and without ASD over the course of early (ages 2-3.5) and middle (ages 5-8) childhood. Using a combination of scores obtained during assessments at both timepoints, the researchers estimated and compared IQ at both time points. For some children, IQ either increased or decreased between the two timepoints; for others, IQ remained stable. Addressing their first hypothesis, the researchers identified four different developmental trajectories for children with ASD, based on these changes in IQ:

• The "High Challenges" group constituted about a quarter (25.5%) of the participants. These children had the lowest average IQ at baseline, and their IQs declined over time.
• The "Stable Low" group had a low and steady IQ, not significantly increasing or decreasing between the two timepoints. This group comprised 17.6% of the children who participated.
• The "Changers" group, slightly more than a third (35.3%) of the children, showed significantly improved IQ scores between the two timepoints.
• The "Lesser Challenges" group, which included 21.6% of the children who participated, had the highest average IQ at baseline. The children in this group had IQ scores that were close to the average IQ of non-ASD children at both time points.

Supporting their second hypothesis, the researchers found that 14% of children in the Lesser Challenges group and 6% of children in the Changers group no longer met criteria for ASD at the second timepoint. Confirming the researchers third hypothesis, children with the greatest increase in IQ (the Changers group), exhibited such significant improvements in their communication abilities by the second timepoint that they were essentially equivalent to children in the Lesser Challenges group. The Stable Low group also showed some increase in their communication abilities, but the severity of their ASD symptoms also increased with time. Finally, contrary to their fourth hypothesis, all four trajectory groups had similar baselines and all demonstrated a similar decline in internalizing behaviors over time. Importantly, they found that none of the groups differed in the amount of interventions they had received.

The results of this study are hopeful, as more than 30% of children showed dramatic increases in IQ over time and 5% no longer met criteria for ASD at the second timepoint. The study is ongoing, and future examination of these children will provide more insight into the long-term trajectory of each of these groups.