Enhanced Visual Contrast Sensitivity in Infant Siblings of Children with Autism Spectrum Disorders (ASD)

Background: We recently reported that 6-month-old “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 luminance (light/dark) contrast sensitivity that is significantly higher than that observed in Low-Risk control infants (McCleery, Allman, Carver & Dobkins, 2007). This finding suggests that enhanced luminance contrast sensitivity may be an early endophenotype of ASD, reflecting a genetically-mediated risk factor for the disorder. Objectives: In the current study, we investigated: 1) whether the group difference previously reported in 6-month-olds replicates in an entirely new sample of subjects, 2) whether infants who go on to develop ASD differ from High-Risk infants who do not, 3) whether group differences can be observed at an earlier time point, i.e., 3-months, and 4) whether gains in contrast sensitivity between 3- and 6-months differ between groups. Methods: The sample of 6-month-olds included 45 Low-Risk controls (infants from families without autism history, 20F, 25M) and 14 High-Risk infants (6F, 8M). The sample of 3-month-olds included 26 Low-Risk infants (11F, 15M) and 14 High-Risk infants (5F, 9M). A subset of infants were tested at both 3- and 6-months (Low-Risk: n = 17, High-Risk: n = 11). An additional 8 infants (7 High-Risk and 1 Low-Risk) went on to develop ASD (based on ADOS/ADI). Using forced-choice preferential looking, we obtained contrast sensitivities for luminance (light/dark) and chromatic (red/green) sinusoidal gratings (0.27 cycles/degree, 4.2 Hz), which are thought to preferentially activate the subcortical Magnocellular and Parvocellular visual pathways, respectively. Results: 1) For 6-month-olds, we replicated our previous findings; High-Risk infants exhibited significantly higher luminance contrast sensitivity (by about 1.6-fold) than Low-Risk infants (p = 0.042, two-tailed t-test), but there were no group differences in chromatic contrast sensitivity. 2) The mean contrast sensitivity of the 8 infants who went on to develop ASD was nearly identical to that of the High-Risk infants who did not develop ASD. 3) For 3-month-olds, High-Risk infants exhibited both significantly higher luminance contrast sensitivity (by about 1.5-fold, p = 0.043) and chromatic contrast sensitivity (by about 1.7-fold, p = 0.064, MS) than Low-Risk infants. This superior performance in High-Risk infants was not due to generally enhanced cognitive performance, as confirmed by their normal Mullen Early Learning scores. 4) For High-Risk infants in the chromatic condition and Low-Risk infants in both the luminance and chromatic conditions, gain in contrast sensitivity between 3- and 6-months was consistent across subjects. By comparison, for the luminance condition in High-Risk infants, gain in contrast sensitivity between the two ages was highly variable. Conclusions: Enhanced contrast sensitivity could provide a potential endophenotypic marker associated with ASD. Because we are currently finding no difference between High-Risk infants who do vs. do not go on to develop ASD, we suggest that factors leading to development of ASD per se may include an inability to compensate for the observed atypicalities, and/or a critical combination of these and other (yet to be tested) atypicalities.