Dissociations of cerebral cortex, subcortical and cerebral white matter volumes in autistic boys

Striatal volume on magnetic resonance imaging and repetitive behaviors in autism

BACKGROUND

The repetitive behaviors seen in autism phenotypically resemble those seen in obsessive-compulsive disorder (OCD) and Tourette Syndrome (TS), disorders in which structural and functional abnormalities of the basal ganglia (BG) are present and correspond to the severity of repetitive behaviors.

METHODS

Seventeen subjects with autism by DSM-IV and Autism Diagnostic Interview (ADI) and 17 matched controls completed a 1.5 T magnetic resonance image (MRI) of the brain. Two blinded researchers, with good inter-rater reliability, outlined the right and left caudate and putamen. Autistic and control BG volumes covaried for total brain volume were compared using analysis of covariance. BG volumes within the autistic group were correlated with the ADI Repetitive Behavior scores (ADI-C domain).

RESULTS

Right caudate volume controlled for total brain volume was significantly larger in autistic subjects than in controls. In addition, right caudate and total putamen volumes correlated positively with repetitive behavior scores on the ADI-C domain, particularly the higher order OCD-like repetitive behaviors.

CONCLUSIONS

Increased right caudate volume in autism is of interest, since this has also been observed in OCD patients. Increased volume of the right caudate and total putamen positively correlated with greater repetitive behaviors, supporting the hypothesis of BG dysfunction associated with repetitive behaviors in autistic adults.

When is the brain enlarged in autism? A meta-analysis of all brain size reports

BACKGROUND

Multiple studies have reported increased brain size in autism, while others have found no difference from normal. These conflicting results may be due to a lack of accounting for age-related changes in brain enlargement, use of small sample sizes, or differences in data acquisition methods.

METHODS

Reports of autism head circumference (HC), magnetic resonance imaging (MRI), and post-mortem brain weight (BW) that met specific criteria were identified and analyzed. Percent difference from normal values (%Diff) and standardized mean differences (SMD) were calculated to compare brain size across studies and measurement methods. Curve fitting, analysis of variance, and heterogeneity analyses were applied to assay the effects of age and measurement type on reported brain size in autism.

RESULTS

A fitted curve of HC and MRI %Diff values from 15 studies revealed a largely consistent pattern of brain size changes. Specifically, brain size in autism was slightly reduced at birth, dramatically increased within the first year of life, but then plateaued so that by adulthood the majority of cases were within normal range. Analysis of variance of MRI and post-mortem %Diff values by age group (young child, older child, adult) and measurement type (MRI, BW) revealed a significant main effect of both age and measurement type, with the youngest ages (2-5) showing the greatest deviation from normal. Random effects heterogeneity analysis revealed a significant effect of age on HC and MRI SMD.

CONCLUSIONS

These findings reveal a period of pathological brain growth and arrest in autism that is largely restricted to the first years of life, before the typical age of clinical identification. Study of the older autistic brain, thus, reflects the outcome, rather than the process, of pathology. Future research focusing on this early process of brain pathology will likely be critical to elucidate the etiology of autism.

Memory and learning in children with 22q11.2 deletion syndrome: evidence for ventral and dorsal stream disruption?

This study examined memory functioning in children and adolescents with 22q11.2 Deletion Syndrome (DS; velocardiofacial syndrome). An overall verbal better than nonverbal memory pattern was evident on the Test of Memory and Learning (TOMAL), with children with 22q11.2 DS performing significantly below their siblings and children with low average IQ but similar to children with autism on facial memory. Children with 22q11 DS also performed significantly below their siblings on tests of verbal working memory. Children with autism performed significantly poorer than the siblings of children with 22q11.2 DS only on their recall of stories. Delayed recall was significantly poorer in children with 22q11.2 DS and children with autism, compared to sibling controls. Although there were no significant group differences on tests of multiple trial verbal or visual learning, a relative weakness was noted with multiple trial visual learning in children with 22q11.2 DS and their siblings, suggesting that an alternative or interactive factor other than the deletion may account for the relatively better verbal compared to nonverbal memory abilities. Deficits in facial memory in children with both 22q11.2 DS and autism suggest disruptions in ventral temporal pathways such as between fusiform gyrus and parahippocampal/hippocampal regions whereas deficits in verbal working memory in children with 22q11.2 DS implicates dorsolateral prefrontal regions, both intimating aberrant white matter pathways.

Structural white matter deficits in high-functioning individuals with autistic spectrum disorder: a voxel-based investigation

A number of imaging and neuropathological studies have reported structural abnormalities in white matter areas such as the corpus callosum in autism spectrum disorder (ASD). Differences in both global brain volume and the size of specific neural structures have been reported. In order to expand these previously reported findings and to describe more precisely the nature of such structural changes, we performed a voxel-based morphometric whole brain analysis, using a group-specific template, in male adolescents with ASD. Fifteen individuals with normal intelligence and ASD, and a group of 16 controls, matched for age, sex, and IQ, were investigated. High-resolution T1-weighted 3D data sets were acquired and analysed. Local white matter volume deficits were found in the corpus callosum, particularly in the anterior splenium and isthmus, and right hemisphere. White matter volume deficits were also found in the left middle temporal, right middle frontal, and left superior frontal gyri. No significant areas of increased white matter volume were found. Our findings support the hypothesis that reduced white matter volume in the corpus callosum and right hemisphere may play a role in the pathophysiology of ASD.

Brain overgrowth in autism during a critical time in development: implications for frontal pyramidal neuron and interneuron development and connectivity

While abnormalities in head circumference in autism have been observed for decades, it is only recently that scientists have begun to focus in on the developmental origins of such a phenomenon. In this article we review past and present literature on abnormalities in head circumference, as well as recent developmental MRI studies of brain growth in this disorder. We hypothesize that brain growth abnormalities are greatest in frontal lobes, particularly affecting large neurons such as pyramidal cells, and speculate how this abnormality might affect neurofunctional circuitry in autism. The relationship to clinical characteristics and other disorders of macrencephaly are discussed.

Brain development in autism: early overgrowth followed by premature arrest of growth

Due to the relatively late age of clinical diagnosis of autism, the early brain pathology of children with autism has remained largely unstudied. The increased use of retrospective measures such as head circumference, along with a surge of MRI studies of toddlers with autism, have opened a whole new area of research and discovery. Recent studies have now shown that abnormal brain overgrowth occurs during the first 2 years of life in children with autism. By 2-4 years of age, the most deviant overgrowth is in cerebral, cerebellar, and limbic structures that underlie higher-order cognitive, social, emotional, and language functions. Excessive growth is followed by abnormally slow or arrested growth. Deviant brain growth in autism occurs at the very time when the formation of cerebral circuitry is at its most exuberant and vulnerable stage, and it may signal disruption of this process of circuit formation. The resulting aberrant connectivity and dysfunction may lead to the development of autistic behaviors. To discover the causes, neural substrates, early-warning signs and effective treatments of autism, future research should focus on elucidating the neurobiological defects that underlie brain growth abnormalities in autism that appear during these critical first years of life.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

What is Known About Autism

Autism is a neurodevelopmental disorder of genetic origins, with a heritability of about 90%. Autistic disorder is classed within the broad domain of pervasive developmental disorders (PDD) that also includes Rett syndrome, childhood disintegrative disorder, Asperger syndrome, and PDD not otherwise specified (PDD-NOS). Prevalence estimates suggest a rate of 0.1-0.2% for autism and 0.6% for the range of PDD disorders. There is considerable phenotypic heterogeneity within this class of disorders as well as continued debate regarding their clinical boundaries. Autism is the prototypical PDD, and is characterized by impairments in three core domains: social interaction, language development, and patterns of behavior (restricted and stereotyped). Clinical pattern and severity of impairment vary along these dimensions, and the level of cognitive functioning of individuals with autism spans the entire range, from profound mental retardation to superior intellect. There is no single biological or clinical marker for autism, nor is it expected that a single gene is responsible for its expression; as many as 15+ genes may be involved. However, environmental influences are also important, as concordance in monozygotic twins is less than 100% and the phenotypic expression of the disorder varies widely, even within monozygotic twins. Multiple susceptibility factors are being explored using varied methodologies, including genome-wide linkage studies, and family- and case-control candidate gene association studies. This paper reviews what is currently known about the genetic and environmental risk factors, neuropathology, and psychopharmacology of autism. Discussion of genetic factors focuses on the findings from linkage and association studies, the results of which have implicated the involvement of nearly every chromosome in the human genome. However, the most consistently replicated linkage findings have been on chromosome 7q, 2q, and 15q. The positive associations from candidate gene studies are largely unreplicated, with the possible exceptions of the GABRB3 and serotonin transporter genes. No single region of the brain or pathophysiological mechanism has yet been identified as being associated with autism. Postmortem findings, animal models, and neuroimaging studies have focused on the cerebellum, frontal cortex, hippocampus, and especially the amygdala. The cerebello-thalamo-cortical circuit may also be influential in autism. There is evidence that overall brain size is increased in some individuals with autism. Presently there are no drugs that produce major improvements in the core social or pragmatic language deficits in autism, although several have limited effects on associated behavioral features. The application of new techniques in autism research is being proposed, including the investigation of abnormal regulation of gene expression, proteomics, and the use of MRI and postmortem analysis of the brain.

Macrocephaly, corpus callosum morphology, and autism

Although the cause of autism is undetermined, a general consensus has been that some type of early aberrant neural development underlies the disorder. Given the increased prevalence of macrocephaly in autism, one theory of abnormal neural development implicates early brain growth resulting in larger brain and head size in autism. Surface area measurements of the midsagittal section of the corpus callosum can be used as an index of neural development and white-matter integrity because the corpus callosum is the major white-matter structure that interconnects the two cerebral hemispheres. The purpose of this study was to obtain corpus callosum surface area, shape, and contour in a sample of non-mentally retarded autistic subjects with macrocephaly (n = 12) and compare them with those of matched (n = 8), typically developing control subjects with benign macrocephaly. No significant differences were found in surface area, shape, or contour between groups, nor did corpus callosum surface area relate to measures of IQ or picture vocabulary. These findings suggest no unique difference in overall regional corpus callosum surface area in autism with macrocephaly.

Larger Brains in Medication Naive High-Functioning Subjects with Pervasive Developmental Disorder

BACKGROUND

Are brain volumes of individuals with Pervasive Developmental Disorder (PDD) still enlarged in adolescence and adulthood, and if so, is this enlargement confined to the gray and/or the white matter and is it global or more prominent in specific brain regions.

METHODS

Brain MRI scans were made of 21 adolescents with PDD and 21 closely matched controls.

RESULTS

All brain volumes, except the white matter, were significantly larger in patients. After correction for brain volume, ventricular volumes remained significantly larger in patients.

CONCLUSIONS

Patients showed a proportional, global increase in gray matter and cerebellum volume, and a disproportional increase in ventricular volumes. Thus, at least in high-functioning patients with PDD, brain enlargement may still be present in adult life.

Superior temporal sulcus anatomical abnormalities in childhood autism: a voxel-based morphometry MRI study

The underlying neurobiology of autism, a severe pervasive developmental disorder, remains unknown. Few neocortical brain MRI abnormalities have been reported. Using rest functional brain imaging, two independent studies have described localized bilateral temporal hypoperfusion in children with primary autism. In order to search for convergent evidence of anatomical abnormalities in autistic children, we performed an anatomical MRI study using optimized whole-brain voxel-based morphometry (VBM). High-resolution 3-D T1-weighted MRI data sets were acquired in 21 children with primary autism (mean age 9.3 +/- 2.2 years) and 12 healthy control children (mean age 10.8 +/- 2.7 years). By comparing autistic children to normal children, we found bilaterally significant decreases of grey matter concentration located in superior temporal sulcus (STS) (P < 0.05 corrected, after small volume correction; SVC). Children with autism were also found to have a decrease of white matter concentration located in the right temporal pole and in cerebellum (P < 0.05, corrected) compared to normal children. These results suggest that autism is associated with bilateral anatomical abnormalities localized in the STS and are remarkably consistent with functional hypoperfusion previously reported in children with autism. The multimodal STS areas are involved in highest level of cortical integration of both sensory and limbic information. Moreover, the STS is now recognized as a key cortical area of the "social brain" and is implicated in social perceptual skills that are characteristically impaired in autism. Therefore, the convergent anatomical and functional temporal abnormalities observed in autism may be important in the understanding of brain behavior relationships in this severe developmental disorder.

Neuroimaging in disorders of social and emotional functioning: what is the question?

Social and emotional processing uses neural systems involving structures ranging from the brain stem to the associational cortex. Neuroimaging research has attempted to identify abnormalities in components of these systems that would underlie the behavioral abnormalities seen in disorders of social and emotional processing, notably autism spectrum disorders, the focus of this review. However, the findings have been variable. The most replicated anatomic finding (a tendency toward large brains) is not modular, and metabolic imaging and functional imaging (although showing substantial atypicality in activation) are not consistent regarding specific anatomic sites. Moreover, autism spectrum disorder demonstrates substantial heterogeneity on multiple levels. Here evidence is marshaled from a review of neuroimaging data to support the claim that abnormalities in social and emotional processing on the autism spectrum are a consequence of systems disruptions in which the behaviors are a final common pathway and the focal findings can be variable, downstream of other pathogenetic mechanisms, and downstream of more pervasive abnormalities.

A question of balance: a proposal for new mouse models of autism

Autism spectrum disorder (ASD) represents a major mental health problem with estimates of prevalence ranging from 1/500 to 1/2000. While generally recognized as developmental in origin, little to nothing is certain about its etiology. Currently, diagnosis is made on the basis of a variety of early developmental delays and/or regressions in behavior. There are no universally agreed upon changes in brain structure or cell composition. No biomarkers of any type are available to aid or confirm the clinical diagnosis. In addition, while estimates of the heritability of the condition range from 60 to 90%, as of this writing no disease gene has been unequivocally identified. The prevalence of autism is three- to four-fold higher in males than in females, but the reason for this sexual dimorphism is unknown. In light of all of these ambiguities, a proposal to discuss potential animal models may seem the heart of madness. However, parsing autism into its individual genetic, behavioral, and neurobiological components has already facilitated a 'conversation' between the human disease and the neuropathology and biochemistry underlying the disorder. Building on these results, it should be possible to not just replicate one aspect of autism but to connect the developmental abnormalities underlying the ultimate behavioral phenotype. A reciprocal conversation such as this, wherein the human disease informs on how to make a better animal model and the animal model teaches of the biology causal to autism, would be highly beneficial.

Imaging data in autism: from structure to malfunction

During the last two decades, neuroimaging studies have improved our knowledge of brain development and contributed to our understanding of disorders involving the developing brain. Differences in cerebral anatomy have been determined in autism spectrum disorder (ASD). Morphological studies by magnetic resonance imaging have provided evidence of structural differences in ASD compared with the normal population. This has enhanced our view of autism as a neurobiological disorder corresponding with different stages and events in brain development. Alterations in volume of the total brain and specifically the cerebellum, frontal lobe, and limbic system have been identified. There appears to be a pattern of increased and then decreased rate of brain growth over time. We integrate these observations with neurobehavioral findings to provide a developmental hypothesis of the pathophysiology of autism.

The autistic brain: birth through adulthood

PURPOSE OF REVIEW

We discuss evidence of brain maldevelopment in the first years of life in autism and new neuroanatomical and functional evidence from later ages of development.

RECENT FINDINGS

Head circumference, an accurate indicator of brain size in children, was reported to jump from normal or below normal size in the first postnatal months in autistic infants to the 84 th percentile by about 1 year of age; this abnormally accelerated growth was concluded by 2 years of age. Infants with extreme head (and therefore brain) growth fell into the severe end of the clinical spectrum and had more extreme neuroanatomical abnormalities. In the frontal and temporal lobes in autism, there have been reports of abnormal increases in gray and white matter at 2 to 4 years; reduced metabolic measures; deviant diffusion tensor imaging results in white matter; underdeveloped cortical minicolumns; and reduced functional activation during socio-emotional, cognitive and attention tasks. Cerebellar abnormalities included abnormal volumes, reduced number and size of Purkinje neurons in the vermis and hemispheres, molecular defects, and reduced functional activation in posterior regions.

SUMMARY

A new neurobiological phenomenon in autism has been described that precedes the onset of clinical behavioral symptoms, and is brief and age-delimited to the first two years of life. The neurobiological defects that precede, trigger, and underlie it may form part of the developmental precursors of some of the anatomical, functional, and behavioral manifestations of autism. Future studies of the first years of life may help elucidate the factors and processes that bring about the unfolding of autistic behavior.

Rett syndrome: a prototypical neurodevelopmental disorder

Rett syndrome, one of the leading causes of mental retardation and developmental regression in girls, is the first pervasive developmental disorder with a known genetic cause. The majority of cases of sporadic Rett syndrome are caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2). MeCP2 binds methylated DNA and likely regulates gene expression and chromatin structure. Genotype/phenotype analysis revealed that the phenotypic spectrum of MECP2 mutations in humans is broader than initially suspected: Mutations have been discovered in Rett syndrome variants, mentally retarded males, and autistic children. A variety of in vivo and in vitro models has been developed that allow analysis of MeCP2 function and pathogenic studies of Rett syndrome. Because the neuropathology of Rett syndrome shares certain features with other neurodevelopmental disorders, a common pathogenic process may underlie these disorders. Thus, Rett syndrome is a prototype for the genetic, molecular, and neurobiological analysis of neurodevelopmental disorders.

Activation of methionine synthase by insulin-like growth factor-1 and dopamine: a target for neurodevelopmental toxins and thimerosal

Methylation events play a critical role in the ability of growth factors to promote normal development. Neurodevelopmental toxins, such as ethanol and heavy metals, interrupt growth factor signaling, raising the possibility that they might exert adverse effects on methylation. We found that insulin-like growth factor-1 (IGF-1)- and dopamine-stimulated methionine synthase (MS) activity and folate-dependent methylation of phospholipids in SH-SY5Y human neuroblastoma cells, via a PI3-kinase- and MAP-kinase-dependent mechanism. The stimulation of this pathway increased DNA methylation, while its inhibition increased methylation-sensitive gene expression. Ethanol potently interfered with IGF-1 activation of MS and blocked its effect on DNA methylation, whereas it did not inhibit the effects of dopamine. Metal ions potently affected IGF-1 and dopamine-stimulated MS activity, as well as folate-dependent phospholipid methylation: Cu(2+) promoted enzyme activity and methylation, while Cu(+), Pb(2+), Hg(2+) and Al(3+) were inhibitory. The ethylmercury-containing preservative thimerosal inhibited both IGF-1- and dopamine-stimulated methylation with an IC(50) of 1 nM and eliminated MS activity. Our findings outline a novel growth factor signaling pathway that regulates MS activity and thereby modulates methylation reactions, including DNA methylation. The potent inhibition of this pathway by ethanol, lead, mercury, aluminum and thimerosal suggests that it may be an important target of neurodevelopmental toxins.

Association between the HOXA1 A218G polymorphism and increased head circumference in patients with autism

BACKGROUND

The HOXA1 gene plays a major role in brainstem and cranial morphogenesis. The G allele of the HOXA1 A218G polymorphism has been previously found associated with autism.

METHODS

We performed case-control and family-based association analyses, contrasting 127 autistic patients with 174 ethnically matched controls, and assessing for allelic transmission disequilibrium in 189 complete trios.

RESULTS

A, and not G, alleles were associated with autism using both case-control (chi(2) = 8.96 and 5.71, 1 df, p <.005 and <.025 for genotypes and alleles, respectively), and family-based (transmission/disequilibrium test chi(2) = 8.80, 1 df, p <.005) association analyses. The head circumference of 31 patients carrying one or two copies of the G allele displayed significantly larger median values (95.0th vs. 82.5th percentile, p <.05) and dramatically reduced interindividual variability (p <.0001), compared with 166 patients carrying the A/A genotype.

CONCLUSIONS

The HOXA1 A218G polymorphism explains approximately 5% of the variance in the head circumference of autistic patients and represents to our knowledge the first known gene variant providing sizable contributions to cranial morphology. The disease specificity of this finding is currently being investigated. Nonreplications in genetic linkage/association studies could partly stem from the dyshomogeneous distribution of an endophenotype morphologically defined by cranial circumference.

Localization of white matter volume increase in autism and developmental language disorder

Increased brain volume in autism appears to be driven mainly by an unexplained white matter enlargement, and we have reported a similar phenomenon in developmental language disorder (DLD). Localization of this enlargement would strongly guide research into its cause, tissue basis, and functional implications. We utilized a white matter parcellation technique that divides cerebral white matter into an outer zone containing the radiate compartment and an inner zone containing sagittal and bridging system compartments. In both high-functioning autism and DLD, enlargement localized to the radiate white matter (all lobes in autism, all but parietal in DLD), whereas inner zone white matter compartments showed no volume differences from controls. Furthermore, in both autism and DLD, later or longer-myelinating regions showed greater volume increases over controls. Neither group showed cerebral cortex, corpus callosum, or internal capsule volume differences from control. Radiate white matter myelinates later than deep white matter; this pattern of enlargement thus is consistent with striking postnatal head circumference percentile increases reported in autism. These findings suggest an ongoing postnatal process in both autism and DLD that is probably intrinsic to white matter, that primarily affects intrahemispheric and corticocortical connections, and that places these two disorders on the same spectrum.

Autism and pervasive developmental disorders

The quantity and quality of research into autism and related conditions have increased dramatically in recent years. Consequently we selectively review key accomplishments and highlight directions for future research. More consistent approaches to diagnosis and more rigorous assessment methods have significantly advanced research, although the boundaries of the 'broader phenotype' remain to be defined and the validity of Asperger's disorder as a discrete syndrome remains controversial. Recent epidemiological studies have shown that Autism Spectrum Disorders are common, but there continues to be debate about the causes of the increase in the frequency with which autism is diagnosed. Psychological research has helped to develop new developmental models for the disorder and there have also been significant advances in the molecular genetics of autism and understanding of the underlying neurobiological processes. Areas important for future research include the study of autism as it first develops, i.e., in infants and very young children, and of specific processes (psychological and neurobiological) which underlie the disorder. Significant challenges lie ahead in evaluating the growing number of treatments for autism and in integrating the results of research into treatment and educational settings.

Postnatal neurodevelopmental disorders: meeting at the synapse?

We often think of neurodevelopmental disorders as beginning before birth, and many certainly do. A handful, however, strike many months after birth, following a period of apparently normal growth and development. Autism and Rett syndrome are two such disorders, and here I consider some of their similarities at the phenotypic and pathogenic levels. I propose that both disorders result from disruption of postnatal or experience-dependent synaptic plasticity.