Is Myelin Content Altered In Young Adults with Autism?

Background:

There is increasing evidence that autism is associated with abnormal white matter development and impaired ‘connectivity’ of neural systems.  Brain connectivity is mediated by myelinated axons, which may be altered or abnormal in autism.  However, to date, no study has directly investigated brain myelin content of autistic individuals in vivo.

Objectives:

The primary objective of this study is to elucidate differences in myelin content in typical and autistic brains. The ultimate aim is to improve our understanding of the underlying neurobiology of autism using non-invasive magnetic resonance imaging (MRI) techniques,

Methods:

Using a new myelin-specific magnetic resonance imaging technique, termed mcDESPOT, brain myelin content was compared between 14 young adults with autism, and 14 matched controls.  Relationships between myelin content and clinical symptom severity within the autistic group (measured by the Autism Diagnostic Instrument, ADI-R); and the severity of autistic traits in both cases and controls, using the Autism Quotient (AQ).

Results:

Individuals with autism demonstrated a highly significant (p < 0.0017) reduction in myelin content in numerous brain regions and white matter tracts.  Affected regions included the frontal, temporal, parietal and occipital lobes.  White matter tracts most affected included the corpus callosum; the uncinate and posterior segments bilaterally; left inferior occipitofrontal tract and cerebellar peduncle, arcuate fasiculus and inferior and superior longitudinal fasciculi; and the right anterior segment.  Further, within autistic individuals, worse interaction score on the ADI-R was significantly related to reduced myelin content in the frontal lobe; genu of the corpus callosum; and the right internal capsule, optic radiation, uncinate, inferior frontal occipital fasciculus and cingulum.  Additionally, increased autistic traits in both cases and controls were significantly related to reduced myelin content of the left cerebellar; genu of the corpus callosum; and left temporal lobe white matter. 

Conclusions:

Individuals with autism have significantly reduced myelin content in numerous brain regions and white matter tracts.  We also provide preliminary evidence that reduced brain myelin content is associated with worsened social development in autistic individuals, and increased autistic traits in both cases and controls.