Follow-up Studies of 4- to 6-Year-Old Siblings of Children with Austism Spectrum Disorders: Visual Contrast Sensitivity, Faces Vs. Objects, and Theory of Mind Tasks

Background: In the last few years, we have reported that “High-Risk” infants, who are thought to carry some of the genes associated with Autism Spectrum Disorders because they have an older sibling diagnosed with the disorder, exhibit: 1) atypical sensitivity to luminance (light/dark) vs. chromatic (red/green) contrast at 6-months (McCleery, Allman, Carver & Dobkins, 2007), 2) Atypical event related potentials to pictures of faces vs. objects at 10-months (McCleery, Akshoomoff, Dobkins & Carver, 2009), and 3) Atypical social referencing skills at 18-months (Cornew, Dobkins, Akshoomoff, McCleery & Carver, 2010), compared to Low-Risk control infants (from families without a history of autism).  These findings suggest possible early endophenotypes of ASD, reflecting genetically-mediated risk factors for the disorder.

Objectives: In the current study, we followed up these children at 4- to 6-years of age on three main measures to determine whether the endophenotypes were still present by this age:  1) contrast thresholds for luminance (light/dark) vs. chromatic (red/green) stimuli, thought to be mediated by the subcortical Magnocellular (M) and Parvocellular (P) pathways, respectively, 2) discrimination thresholds for face and non-face objects (cars), and 3) A Theory of Mind task, which is a test of social cognition.

Methods: The total sample of 4- to 6-year-olds was 26. Because all the children in this study were tested for ASD at 2- and 3-years and found not to on the autism spectrum, the groups referred to as “High-Risk” and “Low-Risk” as infants are herein referred to as siblings of individuals with ASD (SIBS) and typically developing (TD) controls, respectively.  On task (1) children pointed to the side of a monitor that contained either a luminance or chromatic sinusoidal grating (0.27 cycles/degree, 4.2 Hz), and thresholds were measured by varying contrast across trials.  On task (2) children were presented with a morphed face or object (with a certain percentage of one face (or object) vs. another, A vs. B) and pointed to which one of two images (A vs. B) the morph looked more similar to.  On task (3), children were presented with the questions used to assess their knowledge of the desires, beliefs and emotions of others (Wellman & Liu, 2004).

Results: At the current time, we are not finding significant differences between the SIBS and TD groups on any of our three tasks, however, our sample size is still relatively low.  We will also be testing children from our sample who ended up on the spectrum, however, we currently have no children in this category. 

Conclusions: Given that there is a true lack of group differences on our measures, we suggest that the early endophenoptypes we observed in the first 18 months of life are no longer present by 4- to 6-years.  It may be that the children who do not go on to develop ASD (i.e., SIBS) have compensated for and/or recovered from (possibly through intervention or other environmental and/or biological factors) the endophenotype they possessed earlier in life.