White matter reduced streamline coherence in young men with autism and mental retardation.

BACKGROUND AND PURPOSE It has been proposed that white matter alterations might play a role in autistic disorders; however, published data are mainly limited to high-functioning autism. The goal of this study was to apply diffusion tensor imaging (DTI) and fiber tractography (FT) to study white matter in low-functioning autism and the relationship between white matter and cognitive impairment. METHODS Ten low-functioning males with autism (mean age: 19.7 +/- 2.83 years) and 10 age-matched healthy males (mean age: 19.9 +/- 2.64 years) underwent DTI-MRI scanning. fractional anisotropy (FA) maps were analyzed with whole brain voxel-wise and tract-of-interest statistics. Using FT algorithms, white matter tracts connecting the orbitofrontal cortex (OFC) with other brain regions were identified and compared between the two groups. FA mean values of the autistic group were correlated with intelligence quotient (IQ) scores. RESULTS Low-functioning autistic subjects showed a reduced tract volume and lower mean FA values in the left OFC network compared with controls. In the autistic group, lower FA values were associated with lower IQ scores. CONCLUSIONS We showed evidence of OFC white matter network abnormalities in low-functioning autistic individuals. Our results point to a relationship between the severity of the intellectual impairment and the extent of white matter alterations.