White matter pathways extracted from diffusion tensor imaging data for infants at-risk for autism. Warmer colors represent higher fractional anisotropy. Credit: Jason J. Wolff, PhD

Data from 3T MRI scans showed a distinctive pattern of white matter fiber tract development among high-risk infants who develop autism spectrum disorders (ASDs), according to a study published online Feb. 17 in American Journal of Psychiatry. The findings raise the possibility of an imaging biomarker for autism risk, according to researchers.

Previous behavioral research and brain studies have suggested the second 12 months of life represents a pivotal time for brain changes and symptom onset in infants who develop ASDs. As part of the ongoing Infant Brain Imaging Study Network, researchers conducted a prospective, longitudinal study of infants considered high risk for ASD because they had older siblings with ASDs.

The 92 participants underwent diffusion tensor imaging MRI at 6 months and behavioral assessments at 24 months. Most of the children also had additional MRI studies at either or both 12 and 24 months.

At 24 months, 28 infants met criteria for ASDs while 64 infants did not. The two groups differed in white matter fiber tract development as measured by fractional anisotropy (FA).

The study examined 15 separate fiber tracts, and found significant differences in FA growth trajectories in 12 of the 15 tracts between infants who did develop autism versus infants who did not. Infants who later developed autism had elevated FA at six months but then experienced slower development over time. By 24 months of age, infants with autism had lower FA values than infants without autism.

“These preliminary findings suggest that a distinct and pervasive course of white fiber tract development characterizes high-risk infants who go on to develop autistic syndromes,” wrote Jason J. Wolff, PhD, postdoctoral fellow at University of North Carolina’s Carolina Institute for Developmental Disabilities in Chapel Hill, and colleagues.

Because these altered trajectories precede the appearance of clinical symptoms, the researchers suggested that core behavioral features of ASDs may be rooted in an altered neurobiological foundation.

"It's a promising finding," said Wolff in statement. "At this point, it's a preliminary albeit great first step towards thinking about developing a biomarker for risk in advance of our current ability to diagnose autism." An imaging biomarker would allow specialists to diagnose ASDs earlier than the current protocol, which depends on behavioral observations.

The researchers noted that the ability to identify infants at the highest risk for ASDs prior to the full syndrome could allow the implementation of interventions that could reduce or prevent the manifestation of the full syndrome.