Objectives: To identify abnormally as well as normally developing major long-distance cerebral tracts in ASD infants and toddlers.
Methods: We collected 51-angle DTI datasets from N=39 ASD and N=23 typically developing male infants and toddlers (13 months to 43 months) and analyzed FA values in 25 different tracts using a new DTI probabilistic atlas. Subjects were recruited as young as 12-months via the 1-Year Well Baby Check-up approach (Pierce et al., in manuscript) and diagnoses confirmed at later ages.
Results: Logistic regression models show that for multiple cerebral tracts infants and toddlers with greater FA values were more likely to have an ASD diagnosis. Significant tracts included the superior longitudinal fasiculus, forceps minor and uncinate as well as the corpus callosum. Furthermore within these tracts the ability of large FA values to predict ASD was strongest at the youngest ages.
Conclusions: Results are consistent with evidence of early brain overgrowth and suggests that it involves major cerebral white matter tracts as well as cortical gray matter. They are also consistent with MRI evidence of abnormal expansion of specific prefrontal and temporal subregions in ASD infants and toddlers. We theorize that these early developmental defects in connectivity in ASD result from genetic abnormalities in prenatal processes that regulate neuron numbers, migration and neurite outgrowth. We are currently exploring the degree to which DTI profiles could be used alone, or in combination with other imaging indices, as early predictive biomarkers of risk for autism.
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