Differences In Brain Anatomy In Male Adults with High-Functioning Autism Versus Asperger's Syndrome

Background:  The new DSM-5 proposal is to remove the category of Asperger’s disorder/syndrome as a diagnosis. However, it is still not clear at the neurobiological level whether the absence of developmental language delay, which is characteristic of the current diagnosis of Asperger’s disorder/syndrome, contributes to a distinct subtype. To date, no study has investigated this in adults with autism spectrum conditions (ASC), which are now increasingly recognized.

Objectives:  To investigate if there are differences in brain anatomy in male adults with high-functioning ASC with and without developmental language delay, particularly in language areas in the brain.

Methods:  Ninety-one male adults, who were clinically diagnosed with ASC, and whose diagnoses were confirmed by the Autism Diagnostic Interview-Revised (ADI-R), were re-classified as having high-functioning autism (HFA) or Asperger’s syndrome (AS) according to the presence or absence of developmental language delay. They received brain scanning using high-resolution structural magnetic resonance imaging (sMRI). Voxel-based morphometry (VBM) on the segmented and modulated grey matter images, which were registered to a custom template image specific to this study sample, were performed on an age- and IQ-matched subsample composed of 38 subjects with (HFA group) and 42 without developmental language delay (AS group), who showed comparable levels of autistic symptoms and empathizing-systemizing profile. Region-of-interest (ROI) approach was further employed to investigate into the language-related brain structures.

Results:  From VBM, the HFA group showed greater grey matter volume than the AS group in a range of regions, including Broca’s area, left primary sensory-motor cortices, inferior parietal lobule, dorsal medial prefrontal cortex, right visual cortex, bilateral dorsal lateral prefrontal cortices, fusiform and parahippocampal gyri, supplementary motor area, cerebellum, and medulla oblongata. The ROI approach further revealed that in left Heschl’s gyrus, the AS group had a larger volume compared to the HFA group.

Conclusions:  There were brain volumetric differences in male adults with ASC with (HFA) or without (AS) developmental language delay. The difference could reflect a primary characteristic or a compensatory change. Either way, the history of language delay plays a role in brain anatomy in autism, which may be informative for possible subtyping. This data may inform the debate over whether to remove the diagnostic subgroup of Asperger’s disorder/syndrome.