Antonio Y. Hardan

Brain anatomy and development in autism: review of structural MRI studies

Autism is a neurodevelopmental disorder that severely disrupts social and cognitive functions. MRI is the method of choice for in vivo and non-invasively investigating human brain morphology in children and adolescents. The authors reviewed structural MRI studies that investigated structural brain anatomy and development in autistic patients. All original MRI research papers involving autistic patients, published from 1966 to May 2003, were reviewed in order to elucidate brain anatomy and development of autism and rated for completeness using a 12-item check-list. Increased total brain, parieto-temporal lobe, and cerebellar hemisphere volumes were the most replicated abnormalities in autism. Interestingly, recent findings suggested that the size of amygdala, hippocampus, and corpus callosum may also be abnormal. It is conceivable that abnormalities in neural network involving fronto-temporo-parietal cortex, limbic system, and cerebellum may underlie the pathophysiology of autism, and that such changes could result from abnormal brain development during early life. Nonetheless, available MRI studies were often conflicting and could have been limited by methodological issues. Future MRI investigations should include well-characterized groups of autistic and matched healthy individuals, while taking into consideration confounding factors such as IQ, and socioeconomic status.

Validation of proposed DSM-5 criteria for autism spectrum disorder.

OBJECTIVE The primary aim of the present study was to evaluate the validity of proposed DSM-5 criteria for autism spectrum disorder (ASD). METHOD We analyzed symptoms from 14,744 siblings (8,911 ASD and 5,863 non-ASD) included in a national registry, the Interactive Autism Network. Youth 2 through 18 years of age were included if at least one child in the family was diagnosed with ASD. Caregivers reported symptoms using the Social Responsiveness Scale and the Social Communication Questionnaire. The structure of autism symptoms was examined using latent variable models that included categories, dimensions, or hybrid models specifying categories and subdimensions. Diagnostic efficiency statistics evaluated the proposed DSM-5 algorithm in identifying ASD. RESULTS A hybrid model that included both a category (ASD versus non-ASD) and two symptom dimensions (social communication/interaction and restricted/repetitive behaviors) was more parsimonious than all other models and replicated across measures and subsamples. Empirical classifications from this hybrid model closely mirrored clinical ASD diagnoses (90% overlap), implying a broad ASD category distinct from non-ASD. DSM-5 criteria had superior specificity relative to DSM-IV-TR criteria (0.97 versus 0.86); however sensitivity was lower (0.81 versus 0.95). Relaxing DSM-5 criteria by requiring one less symptom criterion increased sensitivity (0.93 versus 0.81), with minimal reduction in specificity (0.95 versus 0.97). CONCLUSIONS Results supported the validity of proposed DSM-5 criteria for ASD as provided in Phase I Field Trials criteria. Increased specificity of DSM-5 relative to DSM-IV-TR may reduce false positive diagnoses, a particularly relevant consideration for low base rate clinical settings. Phase II testing of DSM-5 should consider a relaxed algorithm, without which as many as 12% of ASD-affected individuals, particularly females, will be missed. Relaxed DSM-5 criteria may improve identification of ASD, decreasing societal costs through appropriate early diagnosis and maximizing intervention resources.

Corpus callosum size in autism

Article abstract The size of the seven subregions of the corpus callosum was measured on MRI scans from 22 non–mentally retarded autistic subjects and 22 individually matched controls. Areas of the anterior subregions were smaller in the autistic group. In a subsample, measurements were adjusted for intracranial, total brain, and white matter volumes and the differences between groups remained significant. No differences were found in the other subregions. This observation is consistent with the frontal lobe dysfunction reported in autism.

An MRI Study of Increased Cortical Thickness in Autism

OBJECTIVE The purpose of this study was to examine cortical thickness in autism in light of the postmortem evidence of cortical abnormalities of the disorder. METHOD Magnetic resonance imaging (MRI) scans were acquired from 17 children with autism and 14 healthy comparison subjects, and sulcal and gyral thickness were measured for the total brain and for all lobes. RESULTS Increases in total cerebral sulcal and gyral thickness were observed in children with autism relative to comparison subjects. Similar findings were noted in the temporal and parietal lobes but not in the frontal and occipital lobes. CONCLUSIONS These preliminary findings indicate that increased cortical thickness may contribute to the increased gray matter volume and total brain size that have been observed in autism and may also be related to anomalies in cortical connectivity.

Anatomic evaluation of the orbitofrontal cortex in major depressive disorder

BACKGROUND The orbitofrontal cortex (OFC) plays a major role in neuropsychologic functioning including exteroceptive and interoceptive information coding, reward-guided behavior, impulse control, and mood regulation. This study examined the OFC and its subdivisions in patients with MDD and matched healthy control subjects. METHODS Magnetic resonance imaging (MRI) was performed on 31 unmedicated MDD and 34 control subjects matched for age, gender, and race. Gray matter volumes of the OFC and its lateral and medial subdivisions were measured blindly. RESULTS The MDD patients had smaller gray matter volumes in right medial [two-way analysis of covariance F(1,60) = 4.285; p =.043] and left lateral OFC [F(1,60) = 4.252; p =.044]. Left lateral OFC volume correlated negatively with age in patients but not in control subjects. Male, but not female patients exhibited smaller left and right medial OFC volumes compared with healthy control subjects of the same gender. CONCLUSIONS These findings suggest that patients with MDD have reduced OFC gray matter volumes. Although this reduction might be important in understanding the pathophysiology of MDD, its functional and psychopathologic consequences are as yet unclear. Future studies examining the relationship between specific symptomatic dimensions of MDD and OFC volumes could be especially informative.

A Meta-Analysis of the Corpus Callosum in Autism

BACKGROUND Previous magnetic resonance imaging (MRI) studies have reported reductions in corpus callosum (CC) total area and CC regions in individuals with autism. However, studies have differed concerning the magnitude and/or region contributing to CC reductions. The present study determined the significance and magnitude of reductions in CC total and regional area measures in autism. METHOD PubMed and PsycINFO databases were searched to identify MRI studies examining corpus callosum area in autism. Ten studies contributed data from 253 patients with autism (mean age = 14.58, SD = 6.00) and 250 healthy control subjects (mean age = 14.47, SD = 5.31). Of these 10 studies, 8 reported area measurements for corpus callosum regions (anterior, mid/body, and posterior), and 6 reported area for Witelson subdivisions. Meta-analytic procedures were used to quantify differences in total and region CC area measurements. RESULTS Total CC area was reduced in autism and the magnitude of the reduction was medium (weighted mean d = .48, 95% confidence interval [CI] = .30-.66). All regions showed reductions in size with the magnitude of the effect decreasing caudally (anterior d = .49, mid/body d = .43, posterior d = .37). Witelson subdivision 3 (rostral body) showed the largest effect, indicating greatest reduction in the region containing premotor/supplementary motor neurons. CONCLUSIONS Corpus callosum reductions are present in autism and support the aberrant connectivity hypothesis. Future diffusion tensor imaging studies examining specific fiber tracts connecting the hemispheres are needed to identify the cortical regions most affected by CC reductions.

Brain Volume in Autism

Increased brain size has been observed in individuals with autism with a wide range of cognitive functioning. The purpose of this investigation was to obtain measurements of the brain volume in a sample of nonmentally retarded autistic individuals. Magnetic resonance imaging scans from 16 nonmentally retarded individuals with autism and 19 male volunteer comparison subjects were obtained and the following structures were measured: third, fourth, and lateral ventricles and intracranial and cerebral volumes. Mean cerebral and third ventricle volumes in the autistic subjects were significantly greater than in the controls when adjusted for intracranial volume. No other significant results were found. Our finding of increased brain volume in autism is consistent with previous reports in the literature. Additional longitudinal neuroimaging and, more importantly, neuropathologic studies are warranted to provide a better understanding of the complexities underlying increased brain size in autism. (J Child Neurol 2001;16:421-424).

A randomized controlled pilot trial of oral N-acetylcysteine in children with autism.

BACKGROUND An imbalance in the excitatory/inhibitory systems with abnormalities in the glutamatergic pathways has been implicated in the pathophysiology of autism. Furthermore, chronic redox imbalance was also recently linked to this disorder. The goal of this pilot study was to assess the feasibility of using oral N-acetylcysteine (NAC), a glutamatergic modulator and an antioxidant, in the treatment of behavioral disturbance in children with autism. METHODS This was a 12-week, double-blind, randomized, placebo-controlled study of NAC in children with autistic disorder. Subjects randomized to NAC were initiated at 900 mg daily for 4 weeks, then 900 mg twice daily for 4 weeks and 900 mg three times daily for 4 weeks. The primary behavioral measure (Aberrant Behavior Checklist [ABC] irritability subscale) and safety measures were performed at baseline and 4, 8, and 12 weeks. Secondary measures included the ABC stereotypy subscale, Repetitive Behavior Scale-Revised, and Social Responsiveness Scale. RESULTS Thirty-three subjects (31 male subjects, 2 female subjects; aged 3.2-10.7 years) were randomized in the study. Follow-up data was available on 14 subjects in the NAC group and 15 in the placebo group. Oral NAC was well tolerated with limited side effects. Compared with placebo, NAC resulted in significant improvements on ABC irritability subscale (F = 6.80; p < .001; d = .96). CONCLUSIONS Data from this pilot investigation support the potential usefulness of NAC for treating irritability in children with autistic disorder. Large randomized controlled investigations are warranted.

Increased frontal cortical folding in autism: a preliminary MRI study

The gyrification index (GI), the ratio of total to outer cortical contour, was applied to measure the cerebral folding patterns in autism. GI was examined on a frontal coronal slice obtained from MRI scans of 30 nonmentally retarded individuals with autism and 32 matched healthy controls. In the autistic group, left frontal GI was higher in children and adolescents but not in adults. Cortical folding was decreased bilaterally with age in the total autistic sample but not in controls. These preliminary findings suggest that the gyrification patterns in autism may be abnormal, which could be related to the various cortical anomalies observed in this disorder.

Posterior Fossa Magnetic Resonance Imaging in Autism

OBJECTIVE To determine whether the sizes and volumes of the posterior fossa structures are abnormal in non-mentally retarded autistic adolescents and adults. METHOD Volume measurements of the cerebellum, vermis, and brainstem were obtained from coronal magnetic resonance imaging scans in 16 autistic subjects and 19 group-matched healthy controls. For the purpose of comparison with previous studies, area measurements of the midbrain, pons, medulla, total cerebellar vermis, and its three subregions were also obtained from a larger sample of 22 autistic males (mean age: 22.4 years; range: 12.2-51.8 years) and 22 individually matched controls (mean age 22.4 years; range: 12.9-52.2 years). RESULTS The total volume of the cerebellum and the cerebellar hemispheres were significantly larger in the autistic subjects with and without correcting for total brain volume. Volumes of the vermis and the brainstem and all area measurements did not differ significantly between groups. CONCLUSIONS There is an increase in the volume of the cerebellum in people with autism consistent with the increase in regional and total brain size reported in this developmental disorder. This finding is also concordant with evidence of cerebellar abnormalities from neuropathological and neuropsychological studies that point to the role of this structure, as part of a complex neural system, in the pathophysiology of autism.