Biological Motion Preference and Autism Symptomatology in Adolescents with Fragile X Syndrome

Background:   Fragile X syndrome (FXS) has the highest known penetrance of autism spectrum disorder (ASD) of any single gene disorder, with up to 60% of individuals meeting criteria for ASD, and up to 90% showing at least 1 symptom of the disorder. While symptomatology overlaps significantly between the two disorders, controversy continues to exist over a shared underlying mechanism driving the similar behavioral presentation. 

Objectives:   This study aims to examine preliminary data on a biological motion eye-tracking paradigm collected on individuals with FXS. Preference for biological motion is a foundational social cognitive skill known to be present in typically developing infants from the first days of life, and has been shown to be deficient in individuals with idiopathic autism (Annaz, Campbell, Coleman, Milne & Swettenham, 2011). It is unknown whether this preference for biological motion is intact in individuals with FXS, and whether the presence or absence of a co-morbid diagnosis of ASD is related to this particular social cognitive skill. 

Methods:   Participants included 14 adolescent males with FXS who are part of a larger study on language development (5 FXS, 9 FXS+ASD). Data were collected on an SR Eyelink 1000 plus eye tracker. Stimuli consisted of a split screen video of biological motion point light displays horizontally juxtaposed to random point light displays with the same motion, presented at16° visual angle, for 30 trials, 4-5seconds each. A central fixation point was displayed before each trial that triggered the start of the next trial after a 250ms fixation. Percentage of looking time at biological motion was the time spent looking at biological motion divided by the total looking time at either region of interest (biological motion or random motion control), aggregated across all trials to create a single outcome measure of each participant. Trials with total looking times in both interest areas (i.e. biological motion and random motion) less than 1000ms were removed from the analysis.  Participants also completed the ADOS-2. Severity scores from the ADOS-2 were used in the analysis as a measure of autism symptomatology. Analysis included Pearson-product moment correlations and a one-way ANOVA. 

Results:   No significant correlations were observed between percentage of time looking at biological motion and severity scores on the ADOS-2 (r = -.12, p = .7). An ANOVA to compare mean looking times between the individuals with FXS with and without autism indicated no differences in mean looking time to biological motion, FXS (M = 52.2%, SD =3.56) and FXS+ASD (M = 52.11%, SD=6.38). 

Conclusions:   Findings suggest that severity of autism symptomatology is not related to preferential attention to biological motion in individuals with FXS, and preferential attention to biological motion does not differ between individuals with FXS and FXS+ASD. Given variability in the data, we will examine these data with a larger sample, add a group with idiopathic (non-FXS) autism and examine the effect of other variables (e.g., genetics) to document preferential looking to biological motion in FXS.