Autism and Asperger syndrome (ASP) are neurobiological conditions with
overlapping behavioral symptoms and of unknown etiologies. Results from previous
autism neuroimaging studies have been difficult to replicate, possibly owing
to site differences in subject samples, scanning procedures, and image-processing
methods. We sought (1) to determine whether low-functioning autism (LFA; IQ<70),
high-functioning autism (HFA; IQ≥70), and ASP constitute distinct biological
entities as evidenced by neuroanatomical measures, and (2) to assess for intersite
Case-control study examining coronally oriented 124-section spoiled
gradient echo images acquired on 3 magnetic resonance imaging (MRI) systems,
and processed by BrainImage 5.X. Participants were recruited and underwent
scanning at 2 academic medicine departments. Participants included 4 age-matched
groups of volunteer boys aged 7.8 to 17.9 years (13 patients with LFA, 18
with HFA, 21 with ASP, and 21 control subjects), and 3 volunteer adults for
neuroimaging reliability. Main outcome measures included volumetric measures
of total, white, and gray matter for cerebral and cerebellar tissues.
Intersite differences were seen for subject age, IQ, and cerebellum
measures. Cerebral gray matter volume was enlarged in both HFA and LFA compared
with controls (P = .009 and P =
.04, respectively). Cerebral gray matter volume in ASP was intermediate between
that of HFA and controls, but nonsignificant. Exploratory analyses revealed
a negative correlation between cerebral gray matter volume and performance
IQ within HFA but not ASP. A positive correlation between cerebral white matter
volume and performance IQ was observed within ASP but not HFA.
Lack of replication between previous autism MRI studies could be due
to intersite differences in MRI systems and subjects' age and IQ. Cerebral
gray tissue findings suggest that ASP is on the mild end of the autism spectrum.
However, exploratory assessments of brain-IQ relationships reveal differences
between HFA and ASP, indicating that these conditions may be neurodevelopmentally
different when patterns of multiple measures are examined. Further investigations
of brain-behavior relationships are indicated to confirm these findings.