A clinicopathological study of autism

The functional neuroanatomy of social behaviour: changes in cerebral blood flow when people with autistic disorder process facial expressions

Although high-functioning individuals with autistic disorder (i.e. autism and Asperger syndrome) are of normal intelligence, they have life-long abnormalities in social communication and emotional behaviour. However, the biological basis of social difficulties in autism is poorly understood. Facial expressions help shape behaviour, and we investigated if high-functioning people with autistic disorder show neurobiological differences from controls when processing emotional facial expressions. We used functional MRI to investigate brain activity in nine adults with autistic disorder (mean age +/- standard deviation 37 +/- 7 years; IQ 102 +/- 15) and nine controls (27 +/- 7 years; IQ 116 +/- 10) when explicitly (consciously) and implicitly (unconsciously) processing emotional facial expressions. Subjects with autistic disorder differed significantly from controls in the activity of cerebellar, mesolimbic and temporal lobe cortical regions of the brain when processing facial expressions. Notably, they did not activate a cortical 'face area' when explicitly appraising expressions, or the left amygdala region and left cerebellum when implicitly processing emotional facial expressions. High-functioning people with autistic disorder have biological differences from controls when consciously and unconsciously processing facial emotions, and these differences are most likely to be neurodevelopmental in origin. This may account for some of the abnormalities in social behaviour associated with autism.

Pervasive developmental disorders: a 10-year review

OBJECTIVE

To summarize recent advances about the nature, diagnosis, and treatment of pervasive developmental disorders.

METHOD

Review of Medline databases, books, and book chapters published between July 1989 and November 1999.

RESULTS

Clinical and genetic studies support expansion of the concept of autism to include a broader spectrum of social communication handicaps. The prevalence of autism is approximately 1 per 2,000; the prevalence of autism and Asperger's disorder together is 1 per 1,000. The Checklist for Autism in Toddlers is a useful screening instrument for 18-month-old children; the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule are instruments of choice for research. Although twin and family studies clearly support genetic factors as important in autism, linkage analysis studies indicate that many genes may be involved. There is no one treatment of choice. Social-pragmatic approaches, augmented by individualized strategies and social coaching, may be best for teaching social communication skills. Pharmacological interventions have a limited role in improving social communication, but selective serotonin reuptake inhibitors and atypical neuroleptic medications may help ameliorate aggression, hyperactivity, and other secondary problems.

CONCLUSIONS

Private and government agencies must continue to support basic and applied research.

Occurrence of tics in Asperger's syndrome and autistic disorder

Asperger's syndrome is a condition in the autistic spectrum in which language development is normal. Patients with Asperger's syndrome frequently exhibit repetitive movements (stereotypies), and can have motor and phonic tics in addition to other behavioral abnormalities. We present 12 patients with autistic spectrum disorders who were referred to our Movement Disorders Clinic for evaluation of tics. Eight of the 12 had normal language development and therefore met criteria for Asperger's syndrome. All patients exhibited stereotypic movements; in addition, seven had tics and six of these met diagnostic criteria for Tourette syndrome. Of the six patients with clinical features of both Asperger's syndrome and Tourette syndrome, three had severe congenital sensory deficits. The autistic patients in our series were clinically heterogeneous and though tics were clearly present, other aberrant movements demonstrated by them were harder to classify. Our series confirms the wide range of clinical manifestations in Asperger's syndrome and autism, including tics and other features of Tourette syndrome. Furthermore, it suggests that sensory deprivation contributes to the development of adventitious movements in this population.

Prenatal exposure of rats to valproic acid reproduces the cerebellar anomalies associated with autism

Abnormalities in anatomy and function of the cranial nerve motor nuclei have been demonstrated in some people with autism and can be modeled in rats by exposure to valproic acid during neural tube closure. Reductions in Purkinje cell number and cerebellar volume, particularly of the posterior lobe, have also been reported in people with autism. Thus, a stereological examination of cerebellar morphology was undertaken in valproate-exposed rats. Compared to controls, rats exposed to a single dose of 600-mg/kg sodium valproate on embryonic day 12.5 had significantly fewer Purkinje cells in the cerebellar vermis and a reduction short of significant in the hemispheres. The diminished cell numbers reflect reductions in tissue volume throughout the cerebellum, rather than cell density, which was unaffected in all regions. Within the vermis, the reduction in volume was significantly greater in the posterior lobe than in the anterior lobe. The results parallel those reported for human cases of autism.

Autism--an evolving concept

BACKGROUND

The rapid increase in research endeavour has not kept pace with the advent of well-publicized theories and treatments for autism.

AIMS

To explore some of the newer developments in biological research into autism.

METHOD

A review of recent publications and presentations.

RESULTS

The concept is shifting from the narrow perception of aloof autism, described by Kanner, to a wider one that includes a spectrum extending to a broader, subclinical phenotype. The genetic basis has been established; now we need to discover the location and interaction of the relevant sites. There is considerable interest in the bowel as a pathogenetic agent, particularly in the effects of exogenous opioids and multiple viral infection (the latter posing a public health problem). Also of concern is the role of (potentially treatable) epilepsy, analogous to the Laudau-Kleffner syndrome.

CONCLUSIONS

In the absence of a cure, the implementation of ideas will continue to outstrip factual evidence. Clinicians are challenged by the availability of information (and misinformation), particularly on the internet.

Autism: current theories regarding its pathogenesis and implications for rational pharmacotherapy

Autism is a pervasive developmental disorder that is aetiologically and clinically heterogeneous. Twin and family-genetic studies provide evidence for strong genetic components. An international consortium using an affected sib pair strategy has found a promising linkage to a region on chromosome 7. In 10 to 15% of cases autism is due to associated medical conditions that affect normal brain functioning. Postmortem studies on small case series report cellular abnormalities in the limbic system and cerebellum. Between 10 and 20% of individuals with autism have macrocephalia, which is in accordance with magnetic resonance imaging (MRI) findings of an increased total brain tissue volume and enlargement most prominent in the occipital and parietal lobes. The most robust and well replicated neurobiological abnormality in autism is an elevation of whole blood serotonin (5-hydroxytryptamine; 5-HT) found in over 30% of patients. Pharmacological interventions with serotonin reuptake inhibitors or with atypical neuroleptics that block both dopamine (D2) and serotonin (5-HT2) receptors seem to offer clinical benefit and merit further study.

The screening and diagnosis of autistic spectrum disorders

The Child Neurology Society and American Academy of Neurology recently proposed to formulate Practice Parameters for the Diagnosis and Evaluation of Autism for their memberships. This endeavor was expanded to include representatives from nine professional organizations and four parent organizations, with liaisons from the National Institutes of Health. This document was written by this multidisciplinary Consensus Panel after systematic analysis of over 2,500 relevant scientific articles in the literature. The Panel concluded that appropriate diagnosis of autism requires a dual-level approach: (a) routine developmental surveillance, and (b) diagnosis and evaluation of autism. Specific detailed recommendations for each level have been established in this document, which are intended to improve the rate of early suspicion and diagnosis of, and therefore early intervention for, autism.

An infection-based model of neurodevelopmental damage

Perinatal exposure to infectious agents and toxins is linked to the pathogenesis of neuropsychiatric disorders, but the mechanisms by which environmental triggers interact with developing immune and neural elements to create neurodevelopmental disturbances are poorly understood. We describe a model for investigating disorders of central nervous system development based on neonatal rat infection with Borna disease virus, a neurotropic noncytolytic RNA virus. Infection results in abnormal righting reflexes, hyperactivity, inhibition of open-field exploration, and stereotypic behaviors. Architecture is markedly disrupted in hippocampus and cerebellum, with reduction in granule and Purkinje cell numbers. Neurons are lost predominantly by apoptosis, as supported by increased mRNA levels for pro-apoptotic products (Fas, caspase-1), decreased mRNA levels for the anti-apoptotic bcl-x, and in situ labeling of fragmented DNA. Although inflammatory infiltrates are observed transiently in frontal cortex, glial activation (microgliosis > astrocytosis) is prominent throughout the brain and persists for several weeks in concert with increased levels of proinflammatory cytokine mRNAs (interleukins 1alpha, 1beta, and 6 and tumor necrosis factor alpha) and progressive hippocampal and cerebellar damage. The resemblance of these functional and neuropathologic abnormalities to human neurodevelopmental disorders suggests the utility of this model for defining cellular, biochemical, histologic, and functional outcomes of interactions of environmental influences with the developing central nervous system.

Spatial attention deficits in patients with acquired or developmental cerebellar abnormality

Recent imaging and clinical studies have challenged the concept that the functional role of the cerebellum is exclusively in the motor domain. We present evidence of slowed covert orienting of visuospatial attention in patients with developmental cerebellar abnormality (patients with autism, a disorder in which at least 90% of all postmortem cases reported to date have Purkinje neuron loss), and in patients with cerebellar damage acquired from tumor or stroke. In spatial cuing tasks, normal control subjects across a wide age range were able to orient attention within 100 msec of an attention-directing cue. Patients with cerebellar damage showed little evidence of having oriented attention after 100 msec but did show the effects of attention orienting after 800-1200 msec. These effects were demonstrated in a task in which results were independent of the motor response. In this task, smaller cerebellar vermal lobules VI-VII (from magnetic resonance imaging) were associated with greater attention-orienting deficits. Although eye movements may also be disrupted in patients with cerebellar damage, abnormal gaze shifting cannot explain the timing and nature of the attention-orienting deficits reported here. These data may be consistent with evidence from animal models that suggest damage to the cerebellum disrupts both the spatial encoding of a location for an attentional shift and the subsequent gaze shift. These data are also consistent with a model of cerebellar function in which the cerebellum supports a broad spectrum of brain systems involved in both nonmotor and motor function.

Neuroanatomic contributions to slowed orienting of attention in children with autism

Previous research has demonstrated that adult autistic patients are abnormally slow to orient attention, with degree of slowed orienting associated with severity of cerebellar hypoplasia. This research was extended to children who, at ages two through six, met diagnostic criteria for autism and underwent magnetic resonance imaging (MRI). An average of 3 years later, when old enough to participate in behavioral experiments, the children returned to the laboratory and completed a spatial attention paradigm. Degree of slowed attentional orienting to visual cues was significantly correlated with degree of cerebellar hypoplasia, but not with size of other neuroanatomic regions. Additionally, there was a trend for orienting speed to differ between diagnostic outcome subgroups; children with confirmed diagnoses of autism at time of behavioral testing had larger orienting deficits than those who no longer met diagnostic criteria for autism. This research is among the first to establish a specific brain-behavior link in autistic children.

An MRI study of the basal ganglia in autism

1. High-resolution MRI scans were obtained from 35 relatively high-functioning persons with autism and 36 healthy controls, comparable in age, gender, and IQ. 2. Volumetric measurements were obtained from manual tracing of the bilateral caudate, putamen, and globus pallidus. 3. An increased volume of the caudate nuclei was found in subjects with autism. Caudate enlargement was proportional to increased total brain volume in subjects with autism. 4. Caudate volume was associated with compulsions and rituals, difficulties with minor change, and complex motor mannerisms in autism. 5. Based on evidence of caudate abnormalities, a second MRI study was completed which replicated the finding of caudate enlargement in autism using an independent sample. 6. The caudate may be part of an abnormal distributed neural network in autism and involved in the ritualistic--repetitive behaviors of the disorder.

Appropriate investigations for clinical care versus research in children with autism

As disorders on the autistic spectrum are behaviorally defined, there is no medical test to diagnose autism. The purpose of a medical evaluation is to detect particular etiologies, and manifestations like clinical or subclinical epilepsy or behavior problems that might mandate pharmacologic intervention. Defining a unique syndrome or genetic etiology may benefit other family members, although, currently, specific causes are detectable in only a small minority of individuals on the autistic spectrum. The paper lists elements of the history, examination, and laboratory testing most likely to be informative in clinical practice. Ordering large numbers of tests in the absence of a specific clinical indication is not recommended because it is invasive, wasteful and unlikely to generate useful data. This is not true, of course, in the context of a hypothesis-driven, approved research protocol where collecting standardized data and applying the most up-to-date research technologies is appropriate.

The neuropathology of schizophrenia. A critical review of the data and their interpretation

Despite a hundred years' research, the neuropathology of schizophrenia remains obscure. However, neither can the null hypothesis be sustained--that it is a 'functional' psychosis, a disorder with no structural basis. A number of abnormalities have been identified and confirmed by meta-analysis, including ventricular enlargement and decreased cerebral (cortical and hippocampal) volume. These are characteristic of schizophrenia as a whole, rather than being restricted to a subtype, and are present in first-episode, unmedicated patients. There is considerable evidence for preferential involvement of the temporal lobe and moderate evidence for an alteration in normal cerebral asymmetries. There are several candidates for the histological and molecular correlates of the macroscopic features. The probable proximal explanation for decreased cortical volume is reduced neuropil and neuronal size, rather than a loss of neurons. These morphometric changes are in turn suggestive of alterations in synaptic, dendritic and axonal organization, a view supported by immunocytochemical and ultrastructural findings. Pathology in subcortical structures is not well established, apart from dorsal thalamic nuclei, which are smaller and contain fewer neurons. Other cytoarchitectural features of schizophrenia which are often discussed, notably entorhinal cortex heterotopias and hippocampal neuronal disarray, remain to be confirmed. The phenotype of the affected neuronal and synaptic populations is uncertain. A case can be made for impairment of hippocampal and corticocortical excitatory pathways, but in general the relationship between neurochemical findings (which centre upon dopamine, 5-hydroxytryptamine, glutamate and GABA systems) and the neuropathology of schizophrenia is unclear. Gliosis is not an intrinsic feature; its absence supports, but does not prove, the prevailing hypothesis that schizophrenia is a disorder of prenatal neurodevelopment. The cognitive impairment which frequently accompanies schizophrenia is not due to Alzheimer's disease or any other recognized neurodegenerative disorder. Its basis is unknown. Functional imaging data indicate that the pathophysiology of schizophrenia reflects aberrant activity in, and integration of, the components of distributed circuits involving the prefrontal cortex, hippocampus and certain subcortical structures. It is hypothesized that the neuropathological features represent the anatomical substrate of these functional abnormalities in neural connectivity. Investigation of this proposal is a goal of current neuropathological studies, which must also seek (i) to establish which of the recent histological findings are robust and cardinal, and (ii) to define the relationship of the pathological phenotype with the clinical syndrome, its neurochemistry and its pathogenesis.

Autism and the pervasive developmental disorders

Our understanding of childhood autism and the related pervasive developmental disorders continues to advance in many areas. Nevertheless, the heterogeneity of phenotypic expression presents many challenges, not least to efforts to ascertain the prevalence of the disorders. There is now wide agreement on, and reliable application of, the diagnostic criteria for childhood autism, but there is less agreement on and less reliable application of the criteria for the related disorders atypical autism, pervasive developmental disorder-unspecified and Asperger's syndrome. Evidence about genetic associations indicates that several genes are involved in creating susceptibility to the disorder, and the first steps to identify susceptibility loci have begun. Neuroanatomical models have yet to receive consistent support but early signs of promising advances have been made in pharmacological interventions, and adequate evaluation of behavioural intervention programmes is now underway.

Oculomotor evidence for neocortical systems but not cerebellar dysfunction in autism

OBJECTIVE

To investigate the functional integrity of cerebellar and frontal systems in autism using oculomotor paradigms.

BACKGROUND

Cerebellar and neocortical systems models of autism have been proposed. Courchesne and colleagues have argued that cognitive deficits such as shifting attention disturbances result from dysfunction of vermal lobules VI and VII. Such a vermal deficit should be associated with dysmetric saccadic eye movements because of the major role these areas play in guiding the motor precision of saccades. In contrast, neocortical models of autism predict intact saccade metrics, but impairments on tasks requiring the higher cognitive control of saccades.

METHODS

A total of 26 rigorously diagnosed nonmentally retarded autistic subjects and 26 matched healthy control subjects were assessed with a visually guided saccade task and two volitional saccade tasks, the oculomotor delayed-response task and the antisaccade task.

RESULTS

Metrics and dynamics of the visually guided saccades were normal in autistic subjects, documenting the absence of disturbances in cerebellar vermal lobules VI and VII and in automatic shifts of visual attention. Deficits were demonstrated on both volitional saccade tasks, indicating dysfunction in the circuitry of prefrontal cortex and its connections with the parietal cortex, and associated cognitive impairments in spatial working memory and in the ability to voluntarily suppress context-inappropriate responses.

CONCLUSIONS

These findings demonstrate intrinsic neocortical, not cerebellar, dysfunction in autism, and parallel deficits in higher order cognitive mechanisms and not in elementary attentional and sensorimotor systems in autism.

Autism: the phenotype in relatives

There is broad agreement that genetic influences are central in the development of idiopathic autism. Whether relatives manifest genetically related milder phenotypes, and if so how these relate to autism proper, has proved a more contentious issue. A review of the relevant studies indicates that relatives are sometimes affected by difficulties that appear conceptually related to autistic behaviors. These range in severity from pervasive developmental disorders to abnormalities in only one area of functioning, and possibly extend to related personality traits. Issues involved in clarifying the components of milder phenotypes and their relationship to autism are outlined.