Neurobiology of autism

Brain structural abnormalities in young children with autism spectrum disorder

OBJECTIVE

To explore the specific gross neuroanatomic substrates of this brain developmental disorder, the authors examine brain morphometric features in a large sample of carefully diagnosed 3- to 4-year-old children with autism spectrum disorder (ASD) compared with age-matched control groups of typically developing (TD) children and developmentally delayed (DD) children.

METHODS

Volumes of the cerebrum, cerebellum, amygdala, and hippocampus were measured from three-dimensional coronal MR images acquired from 45 children with ASD, 26 TD children, and 14 DD children. The volumes were analyzed with respect to age, sex, volume of the cerebrum, and clinical status.

RESULTS

Children with ASD were found to have significantly increased cerebral volumes compared with TD and DD children. Cerebellar volume for the ASD group was increased in comparison with the TD group, but this increase was proportional to overall increases in cerebral volume. The DD group had smaller cerebellar volumes compared with both of the other groups. Measurements of amygdalae and hippocampi in this group of young children with ASD revealed enlargement bilaterally that was proportional to overall increases in total cerebral volume. There were similar findings of cerebral enlargement for both girls and boys with ASD. For subregion analyses, structural abnormalities were observed primarily in boys, although this may reflect low statistical power issues because of the small sample (seven girls with ASD) studied. Among the ASD group, structural findings were independent of nonverbal IQ. In a subgroup of children with ASD with strictly defined autism, amygdalar enlargement was in excess of increased cerebral volume.

CONCLUSIONS

These structural findings suggest abnormal brain developmental processes early in the clinical course of autism. Research currently is underway to better elucidate mechanisms underlying these structural abnormalities and their longitudinal progression.

Effects of genetic background on neonatal Borna disease virus infection-induced neurodevelopmental damage. I. Brain pathology and behavioral deficits

The pathogenic mechanisms of gene-environment interactions determining variability of human neurodevelopmental disorders remain unclear. In the two consecutive papers, we used the neonatal Borna disease virus (BDV) infection rat model of neurodevelopmental damage to evaluate brain pathology, monoamine alterations, behavioral deficits, and responses to pharmacological treatments in two inbred rat strains, Lewis and Fisher344. The first paper reports that despite comparable virus replication and distribution in the brain of both rat strains, neonatal BDV infection produced significantly greater thinning of the neocortex in BDV-infected Fisher344 rats compared to BDV-infected Lewis rats, while no strain-related differences were found in BDV-induced granule cell loss in the dentate gyrus of the hippocampus and cerebellar hypoplasia. Unlike BDV-infected Lewis rats, more severe BDV-induced brain pathology in Fisher344 rats was associated with (1) greater locomotor activity to novelty and (2) impairment of habituation and prepulse inhibition of the acoustic startle response. The present data demonstrate that the same environmental insult can produce differential neuroanatomical and behavioral abnormalities in genetically different inbred rat strains.

Bornavirus tropism and targeted pathogenesis: virus-host interactions in a neurodevelopmental model

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Bornavirus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Distinct losses in DA pathways in the adult infection model, and the associated dramatic movement disorder that accompanies it, make it an intriguing model for tardive dyskinesia and dystonic syndromes. The neuropathologic, physiologic, and neurobehavioral features of BDV infection of neonates indicate that it not only provides a useful model for exploring the mechanisms by which viral and immune factors may damage developing neurocircuitry, but also has significant links to the range of biologic, neurostructural, locomotor, cognitive, and social deficits observed in serious neuropsychiatric illnesses such as autism.

Linkage and association of the glutamate receptor 6 gene with autism

A genome scan was previously performed and pointed to chromosome 6q21 as a candidate region for autism. This region contains the glutamate receptor 6 (GluR6 or GRIK2) gene, a functional candidate for the syndrome. Glutamate is the principal excitatory neurotransmitter in the brain and is directly involved in cognitive functions such as memory and learning. We used two different approaches, the affected sib-pair (ASP) method and the transmission disequilibrium test (TDT), to investigate the linkage and association between GluR6 and autism. The ASP method, conducted with additional markers on the 51 original families and in eight new sibling pairs, showed a significant excess of allele sharing, generating an elevated multipoint maximum LOD score (ASPEX MLS = 3.28). TDT analysis, performed in the ASP families and in an independent data set of 107 parent-offspring trios, indicated a significant maternal transmission disequilibrium (TDTall P = 0.0004). Furthermore, TDT analysis (with only one affected proband per family) showed significant association between GluR6 and autism (TDT association P = 0.008). In contrast to maternal transmission, paternal transmission of GluR6 alleles was as expected in the absence of linkage, suggesting a maternal effect such as imprinting. Mutation screening was performed in 33 affected individuals, revealing several nucleotide polymorphisms (SNPs), including one amino acid change (M867I) in a highly conserved domain of the intracytoplasmic C-terminal region of the protein. This change is found in 8% of the autistic subjects and in 4% of the control population and seems to be more maternally transmitted than expected to autistic males (P = 0.007). Taken together, these data suggest that GluR6 is in linkage disequilibrium with autism.

Secretin and sleep in children with autism

The objectives of this pilot study were 1) to examine possible effects of secretin infusions on sleep-wake state organization in children with autism, and 2) to assess the feasibility of home recordings using time-lapse videosomnography in children with autism. Participants were a subset of subjects from two double blind, placebo-control, multi-center clinical trials. One trial, the UC Irvine study, assessed the effects of porcine secretin vs. saline infusions on children's behavior, language and IQ. The UC Davis trial assessed the effects of synthetic human secretin vs. saline infusions on behavior, language and gastrointestinal function. The sleep study enrolled some of the children from each of the two trials to observe possible secretin effects on sleep. To examine sleep, the UC Irvine trial used the Children's Sleep Habits Questionnaire and daily sleep diaries, whereas the UC Davis study used home-recorded time-lapse videosomnography. Because of the small sample size, the results from both trials are preliminary. They suggest that secretin, porcine or synthetic, does not improve sleep-wake state organization dramatically.

The abnormal regulation of gene expression in autistic brain tissue

Autism is a pervasive developmental disorder of unknown etiology. It is likely caused by mutations in one or more genes. One approach to understanding the molecular changes that occur in autism is to measure gene expression in post-mortem brain samples from individuals diagnosed with autism. This may be accomplished with techniques such as cDNA microarrays or subtractive hybridization. In general, gene expression is regulated as a function of body region, developmental time, and physiological state. A premise of the approaches we describe is that gene expression is regulated in cells from autistic individuals as a consequence of the disease process. It may be useful to detect such changes in order to identify selective biological markers for autism. Additionally, the abnormal regulation of gene expression may reveal cellular pathways that have been disrupted, suggesting strategies for therapeutic intervention.

Borna disease virus infection of adult and neonatal rats: models for neuropsychiatric disease

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Borna disease virus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Note in press: Since this chapter was submitted, several manuscripts have been published that extend findings reported here and support the relevance of BDV infections of neonatal Lewis rats as models for investigating mechanisms of neurodevelopmental damage in autism. Behavioral abnormalities, including disturbed play behavior and chronic emotional overactivity, have been described by Pletnikov et al. (1999); inhibition of responses to novel stimuli were described by Hornig et al. (1999); loss of Purkinje cells following neonatal BDV infection has been demonstrated by Eisenman et al. (1999), Hornig et al. (1999), and Weissenböck et al. (2000); and alterations in cytokine gene expression have been reported by Hornig et al. (1999), Plata-Salaman et al. (1999) and Sauder et al. (1999).

Plasma fatty acid levels in autistic children

Phospholipid fatty acids are major structural components of neuronal cell membranes, which modulate membrane fluidity and hence function. Evidence from clinical and biochemical sources have indicated changes in the metabolism of fatty acids in several psychiatric disorders. We examined the phospholipid fatty acids in the plasma of a population of autistic subjects compared to mentally retarded controls. Our results showed a marked reduction in the levels of 22: 6n-3 (23%) in the autistic subjects, resulting in significantly lower levels of total (n-3) polyunsaturated fatty acids (PUFA) (20%), without significant reduction in the (n-6) PUFA series, and consequently a significant increase in the (n-6)/(n-3) ratio (25%). These variations are discussed in terms of potential differences in PUFA dietary intake, metabolism, or incorporation into cellular membranes between the two groups of subjects. These results open up interesting perspectives for the investigation of new biological indices in autism. Moreover, this might have new therapeutic implications in terms of child nutrition.

Evidence for a susceptibility gene for autism on chromosome 2 and for genetic heterogeneity

Although there is considerable evidence for a strong genetic component to idiopathic autism, several genomewide screens for susceptibility genes have been performed with limited concordance of linked loci, reflecting either numerous genes of weak effect and/or sample heterogeneity. Because decreasing sample heterogeneity would increase the power to identify genes, the effect on evidence for linkage of restricting a sample of autism-affected relative pairs to those with delayed onset (at age >36 mo) of phrase speech (PSD, for phrase speech delay) was studied. In the second stage of a two-stage genome screen for susceptibility loci involving 95 families with two or more individuals with autism or related disorders, a maximal multipoint heterogeneity LOD score (HLOD) of 1.96 and a maximal multipoint nonparametric linkage (NPL) score of 2.39 was seen on chromosome 2q. Restricting the analysis to the subset of families (n=49) with two or more individuals having a narrow diagnosis of autism and PSD generated a maximal multipoint HLOD score of 2.99 and an NPL score of 3.32. The increased scores in the restricted sample, together with evidence for heterogeneity in the entire sample, indicate that the restricted sample comprises a population that is more genetically homogeneous, which could therefore increase the likelihood of positional cloning of susceptibility loci.

Measles-mumps-rubella vaccine and autistic spectrum disorder: report from the New Challenges in Childhood Immunizations Conference convened in Oak Brook, Illinois, June 12-13, 2000

BACKGROUND

Parents and physicians are understandably concerned about the causes and treatment of autism, a devastating disease that affects the entire family. Although much has been learned about autism, there are many gaps in our knowledge about what causes the disorder and how it can be prevented. Autistic symptoms occur along a spectrum, often referred to as autistic spectrum disorder (ASD). Concern has been raised about a possible association between measles-mumps-rubella (MMR) vaccine and inflammatory bowel disease (IBD) and ASD, especially autism with regression. Also, increased requests for educational services related to ASD have raised concerns about possible increases in the incidence of ASD.

METHODS

On June 12-13, 2000, the American Academy of Pediatrics (AAP) convened a conference titled "New Challenges in Childhood Immunizations" in Oak Brook, Illinois. At this conference, parents, practitioners, and scientists presented information and research on MMR vaccine and ASD. Attendees included representatives from select AAP committees and sections as well as federal and other organizations that address related issues. The multidisciplinary panel of experts reviewed data on what is known about the pathogenesis, epidemiology, and genetics of ASD and the available data on hypothesized associations with IBD, measles, and MMR vaccine. Supplemental information was requested from authors who have proposed the hypotheses and other experts in relevant areas.

RESULTS

Autism is a complex disorder of uncertain and probably multiple etiologies. Genetic predisposition to ASD may involve as many as 10 genes. Many experts believe that the abnormal brain development in autism occurs before 30 weeks' gestation in most instances. In utero rubella is a known cause of autism. Animal model data support the biologic plausibility that exposure to yet unrecognized infectious or other environmental agents could cause ASD. Several factors may contribute to apparent increases in incidence of ASD in recent years. Most data indicate increased recognition and reporting as primary factors, but the epidemiologic data are insufficient to determine if there has been a true increase in the incidence of ASD. Increased reporting of ASD in recent years has occurred long after the introduction of MMR vaccine in the United States in 1971 and widespread use of this vaccine in the 1970s for routine immunization of children at 12 to 15 months of age. Appropriate detailed studies are needed to define the true incidence and prevalence of ASD. Epidemiologic studies in Europe indicate no association between MMR vaccine and ASD. Some children with ASD have gastrointestinal symptoms, but an increased rate of any specific gastrointestinal disorder in children with ASD has not been established. Studies to detect evidence of measles virus in intestinal tissue specimens from patients with IBD or autism with gastrointestinal symptoms have not used uniform techniques. Several laboratories have found no evidence of measles viruses in tissue specimens from patients with IBD, but 2 groups have found evidence of measles virus using different techniques. A group that found evidence of measles virus in affected tissue specimens from patients with IBD has also reported detecting portions of measles virus in peripheral blood lymphocytes and intestinal tissue specimens from patients with autism and gastrointestinal disorders. Finding a portion of a virus using molecular techniques does not constitute evidence for a causal relationship, because some viruses persist in unaffected hosts. Additional controlled studies in several laboratories are needed to determine if portions of measles virus persist in intestinal and other tissues of people with and without gastrointestinal disease and/or ASD.

CONCLUSIONS

Although the possible association with MMR vaccine has received much public and political attention and there are many who have derived their own conclusions based on personal experiences, the available evidence does not support the hypothesis that MMR vaccine causes autism or associated disorders or IBD. Separate administration of measles, mumps, and rubella vaccines to children provides no benefit over administration of the combination MMR vaccine and would result in delayed or missed immunizations. Pediatricians need to work with families to ensure that children are protected early in the second year of life from these preventable diseases. Continued scientific efforts need to be directed to the identification of the causes of ASD.

Clinical considerations in the diagnosis of autism spectrum disorders

The diagnosis of autistic spectrum disorders (ASD) is being made more frequently in children and at younger ages. This paper discusses various factors to be considered in the screening of autism, early features of presentation, relevant to assessment and diagnosis, subtypes or different syndromes within the spectrum of autistic conditions including Asperger syndrome, the differential diagnosis from learning and language disorders and the medical and behavioural commonly associated disorders.

Technical report: the pediatrician's role in the diagnosis and management of autistic spectrum disorder in children

Autism and its milder variants are not rare. Most pediatricians will have the opportunity to provide a medical home for a child with autism. This technical report serves to complement and expand on the information in the accompanying policy statement to increase the pediatrician's fund of knowledge and comfort level in caring for children with autism. In so doing, it is anticipated that earlier diagnosis and referral for appropriate intervention will be possible and that this will, in turn, have a positive effect on long-term outcomes for children with autism and their families.

Lamotrigine therapy for autistic disorder: a randomized, double-blind, placebo-controlled trial

In autism, glutamate may be increased or its receptors up-regulated as part of an excitotoxic process that damages neural networks and subsequently contributes to behavioral and cognitive deficits seen in the disorder. This was a double-blind, placebo-controlled, parallel group study of lamotrigine, an agent that modulates glutamate release. Twenty-eight children (27 boys) ages 3 to 11 years (M = 5.8) with a primary diagnosis of autistic disorder received either placebo or lamotrigine twice daily. In children on lamotrigine, the drug was titrated upward over 8 weeks to reach a mean maintenance dose of 5.0 mg/kg per day. This dose was then maintained for 4 weeks. Following maintenance evaluations, the drug was tapered down over 2 weeks. The trial ended with a 4-week drug-free period. Outcome measures included improvements in severity and behavioral features of autistic disorder (stereotypies, lethargy, irritability, hyperactivity, emotional reciprocity, sharing pleasures) and improvements in language and communication, socialization, and daily living skills noted after 12 weeks (the end of a 4-week maintenance phase). We did not find any significant differences in improvements between lamotrigine or placebo groups on the Autism Behavior Checklist, the Aberrant Behavior Checklist, the Vineland Adaptive Behavior scales, the PL-ADOS, or the CARS. Parent rating scales showed marked improvements, presumably due to expectations of benefits.

Magnetoencephalography and magnetic source imaging in children

Magnetoencephalography is a technique that detects the magnetic fields associated with the intracellular current flow within neurons, unlike electroencephalography, which measures extracellular volume currents. Superconducting quantum interference devices are used to amplify these very small magnetic field signals. Magnetic source imaging is the combination of functional data derived from magnetoencephalographic recordings coregistered with structural magnetic resonance imaging (MRI). The utility of magnetic source imaging lies in the combination of the submillisecond temporal resolution of magnetoencephalography with the precise anatomic images provided by magnetic resonance imaging. As such, magnetic source imaging is a useful tool for noninvasive localization of the epileptogenic zone in children who are candidates for epilepsy surgery. Similarly, using magnetoencephalographic recordings with evoked and event-related potentials, magnetic source imaging holds great promise as a noninvasive method for precise localization of somatosensory, motor, language, visual, and auditory cortex. Finally, magnetic source imaging is proving a valuable research tool in the investigation of epilepsy, head trauma, brain plasticity, and disorders of language, memory, cognition, and executive function in children.

Neonatal Borna disease virus infection (BDV)-induced damage to the cerebellum is associated with sensorimotor deficits in developing Lewis rats

Neonatal Borna disease virus (BDV) infection of the brain produces developmental damage to the cerebellum in Lewis rats, with minimal classical inflammatory responses. In the present study, we assessed the consequences of this damage by measuring motor coordination and postural skills in developing (postnatal days 4 to 30) Lewis rats that were neonatally infected with BDV. Neonatal BDV infection-induced motor impairments were selective and correlated with the time course of BDV damage to cerebellar development. BDV-induced motor deficits were not seen until the end of postnatal week 2. By postnatal week 3, BDV-infected rats had deficits in negative geotropism, fore- and hind limb placing and grasping. BDV-infected rats also exhibited deficits in the ability to hold on to a bar and to cross a suspended bar. Neonatal BDV infection induced impairments in the acoustic startle response. Compared to controls, neonatally BDV-infected rats exhibited attenuated habituation of the acoustic startle at postnatal day (PND) 23 and decreased startle responsiveness at PND 30. Prepulse inhibition of the acoustic startle remained unaltered in BDV-infected rats. The data demonstrate that neonatal BDV brain infection of rats can be a valuable animal model system for studying the relationship between abnormal brain development and resultant behavioral deficits. Further studies of this model may elucidate specific pathogenic mechanisms that that may have implications in the study of neurodevelopmental human disorders.

A comparative study of genetic and neurobiological findings in disintegrative psychosis and infantile autism

Although disintegrative psychosis (DP) was first described in 1908, the validity of the syndrome has not yet been fully documented. To investigate the validity of DP as defined in ICD-9, 13 cases of DP were compared with 39 cases of infantile autism with reference to lifetime parental psychopathology, neuroradiological findings and genetic abnormalities. The groups were matched for gender, age, intellectual level and social class. Apart from a significantly higher rate of electroencephalogram abnormalities in the disintegrative group there was very little in the neurobiological background to support a clear distinction between DP and infantile autism.

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.

The amygdala theory of autism

Brothers (Brothers L. Concepts in Neuroscience 1990;1:27-51) proposed a network of neural regions that comprise the "social brain", which includes the amygdala. Since the childhood psychiatric condition of autism involves deficits in "social intelligence", it is plausible that autism may be caused by an amygdala abnormality. In this paper we review the evidence for a social function of the amygdala. This includes reference to the Kluver-Bucy syndrome (which Hetzler and Griffin suggested may serve as an animal model of autism). We then review evidence for an amygdala deficit in people with autism, who are well known to have deficits in social behaviour. This includes a detailed summary of our recent functional magnetic resonance imaging (fMRI) study involving judging from the expressions of another person's eyes what that other person might be thinking or feeling. In this study, patients with autism or AS did not activate the amygdala when making mentalistic inferences from the eyes, whilst people without autism did show amygdala activity. The amygdala is therefore proposed to be one of several neural regions that are abnormal in autism. We conclude that the amygdala theory of autism contains promise and suggest some new lines of research.

Epilepsy in adolescents and young adults with autistic disorder

Since the first description by Kanner (1943) the association between autistic disorder (AD) and epilepsy has been observed in 4-42% of patients. Some authors reported that seizures prevailed in adolescence but a systematic investigation has never been undertaken. We examined retrospectively 60 patients divided into two groups (with and without epilepsy and EEG paroxysmal abnormalities) with AD unrelated to a congenital or acquired encephalopathy (mean age 17 years 2 months). The aim was to investigate epilepsy, EEG paroxysmal abnormalities and possible etiological factors. The prevalence of epilepsy was 38.3%, much higher than that in a normal population of a similar age (6.6 per thousand). The prevalence of EEG paroxysmal abnormalities without epilepsy was 6.7%, higher than that in a population of adolescents and adults with psychiatric pathologies (2. 6%). Seizure onset was after age 12 years in 66.7% of cases. The most common type of epilepsy was partial in 65.2% and four patients (17.4%) had a benign childhood epilepsy with centro-temporal spikes. At the last observation 44.4% of patients had been seizure-free for 2 years or more. There were no organic factors influencing the development of epilepsy but familial and personal antecedents, mental retardation and CT scan/MRI data may suggest an early brain dysfunction responsible for AD and epilepsy.

High throughput analysis of gene expression in the human brain

The human brain is thought to have the greatest complexity of gene expression of any region of the body, reflecting the diverse functions of neurons and glia. Studies of gene expression in the human brain may yield fundamental information about the phenotype of brain cells in different stages of development, in different brain regions, and in different physiological and pathological states. As the human genome project nears completion, several technological advances allow the analysis of thousands of expressed genes in a small brain sample. This review describes available sources of human brain material, and several high throughput techniques used to measure the expression of thousands of genes. These techniques include expressed sequence tag (EST) sequencing of cDNA libraries; differential display; subtractive hybridization; serial analysis of gene expression (SAGE); and the emerging technology of high density DNA microarrays. Measurement of gene expression with microarrays and other technologies has potential applications in the study of human brain diseases, including cognitive disorders for which animal models are typically not available. Gene expression measurements may be used to identify genes that are abnormally regulated as a secondary consequence of a disease state, or to identify the response of brain cells to pharmacological treatments.

Sleep abnormalities in mentally retarded autistic subjects: Down's syndrome with mental retardation and normal subjects

We compared sleep parameters in mentally retarded infantile autism (MRIA) and mentally retarded Down's syndrome (MRDS) by means of polysomnography, evaluating traditional analysis with particular attention to the phasic components in each disorder. Data were compared with those obtained in normal subjects matched for age and sex. Mental age, Intellectual Quotient and the Childhood Autism Rating Scale were performed to obtain an estimation of the neuropsychological deficit. Abnormalities of phasic components of sleep and the presence of REM sleep components into non-REM sleep were observed in both MRIA and MRDS even if in different ways. In fact, MRDS subjects presented a reduction of REM sleep percentage and R index (number of high frequency REMs against number of low frequency REMs) and this was positively correlated to a low IQ. Unlike MRDS subjects, MRIA subjects did not show any parallelism between intellectual abilities and REM sleep deficit. In addition, the presence of undifferentiated sleep in autistic subjects implies a maturational deficit that is still present in adulthood. Finally, a high R index in MRIA was observed. This finding, which is not present in MRDS, could represent an estimation of the disorganized arrival of information caused by a dyscontrol or a reduction of inhibitor pathway. With reference to sleep mechanisms, our results suggest that the cognitive deficit in MRIA may differ from that of MRDS subjects. A maturational deficit of CNS with a dysfunction of brainstem monoaminergic neurons could represent the underlying mechanism.

The möbius sequence: a relook

BACKGROUND

The constellations of findings often referred to as Mobius syndrome might be better described as Mobius sequence, because the term sequence defines a cascade of secondary events after an embryonic insult from heterogeneous causes. Classic clinical findings include evidence of sixth and seventh cranial nerve involvement, often with associated malformations of limbs, craniofacial structures, and other cranial nerves.

METHODS

A prospective study was undertaken in Sweden of 25 patients who showed characteristic findings of Mobius sequence.

RESULTS

Of the patients who did not have strabismus surgery, 10 patients had straight eyes in the primary position, 7 had esotropia, 2 had exotropia, and 1 had hypertropia. All had significant limitation of abduction, except 1 patient with exotropia who showed minimal underaction on abduction but a large limitation of adduction. In the description in these early cases, some patients manifested a clinical pattern resembling a horizontal gaze paresis. Narrowing of the palpebral fissure on adduction similar to that seen in Duane syndrome was observed in a few cases. Two patients had ptosis. Nineteen patients had diminished facial expression bilaterally, often asymmetric, and 6 cases appeared to be unilateral. Seven patients had abnormal tearing. Associated systemic findings included Poland anomaly (2), club feet or other limb anomalies (8), micrognathia (8), tongue malformations (17), cleft palate (5), and speech problems (18). An unusual finding was autism syndrome (6) or autism-like syndrome (1).

CONCLUSIONS

The associated findings in Mobius sequence may give further clues to the location and timing of the developmental disturbance. The wide range of ocular motility patterns suggests that the previous concept of a lesion solely in the sixth nerve nucleus is an inadequate explanation for these findings.

MRI-based brain volumetrics: emergence of a developmental brain science

MRI-based brain volumetrics is an established methodology of great versatility and reliability with a broad range of potential applications in medicine and basic human brain science. We consider here, more theoretical implications of brain tissue volumes. Specifically, we suggest that volume is an evolutionarily and developmentally regulated fundamental property of tissue, in this instance the brain and its component structures. Within this framework (1), regularities in relative variation of volumes with respect to mean volume of a structure are viewed as systematic manifestations of the rules of histogenetic process (2), regularities in the relative strength of correlation of volumes of structures are suggested to reflect constraints which serve systematically the requirements of neural systems operation. These hypotheses, if supported by extensive observation, may guide the design of applications of MRI based volumetric analysis of the human brain.

Social intelligence in the normal and autistic brain: an fMRI study

There is increasing support for the existence of 'social intelligence' [Humphrey (1984) Consciousness Regained], independent of general intelligence. Brothers et al. 1990) J. Cog. Neurosci., 4, 107-118] proposed a network of neural regions that comprise the 'social brain': the orbito-frontal cortex (OFC), superior temporal gyrus (STG) and amygdala. We tested Brothers' theory by examining both normal subjects as well as patients with high-functioning autism or Asperger syndrome (AS), who are well known to have deficits in social intelligence, and perhaps deficits in amygdala function [Bauman & Kemper (1988) J. Neuropath. Exp. Neurol., 47, 369]. We used a test of judging from the expressions of another person's eyes what that other person might be thinking or feeling. Using functional magnetic resonance imaging (fMRI) we confirmed Brothers' prediction that the STG and amygdala show increased activation when using social intelligence. Some areas of the prefrontal cortex also showed activation. In contrast, patients with autism or AS activated the fronto-temporal regions but not the amygdala when making mentalistic inferences from the eyes. These results provide support for the social brain theory of normal function, and the amygdala theory of autism.

Neuroimaging in autism

BACKGROUND

Childhood autism is a developmental disorder with distinctive clinical features and characteristic cognitive deficits. Neuroimaging techniques have been extensively used in the study of autism and related disorders.

METHOD

Recent important literature reported on structural and functional neuroimaging in autism was reviewed and discussed in the context of other neurobiological research findings.

RESULTS

Various abnormalities of brain structure and function have been proposed, but no focal defect has been reliably demonstrated. Important findings, so far, include increased brain volume, structural abnormality in frontal lobe and corpus callosum in a proportion of autistic individuals. Functional neuroimaging findings emphasised the imbalance in inter-regional and inter-hemispheric brain metabolism and blood flow as well as abnormality in the anterior cingulate gyrus.

CONCLUSION

The research to date has been hindered by methodological difficulties. However, hypothesis-driven research, particularly involving activation studies and neurotransmitter/neuroreceptor activities, using functional neuroimaging will be very useful in unravelling the enigma associated with this intriguing and distressing condition.