Neurobiology of autism

For others: Epistasis and the evolutionary survival of an extreme tail of the quantitative distribution of autistic assets

The ongoing paradigm shift from the traditional qualitative dichotomy concept to the quantitative framework increases the necessity of an evolutionary implication and interpretation of the presence of a hypo-reproductive behavioral extreme (autism) with strong genetic contribution. As a theoretical challenge to explain the survival of the dimensional distribution of autistic traits, an epistasis-associated oscillation of fitness outcomes is proposed. In this hypothesis, an allele could contribute to the existence of both phenotypic extreme tails and the hypothesized genetic machinery (quantitative trait loci) for autism would necessarily be common in the entire human population. The postulated autism genes would allow autistics to enjoy autistic traits and assets and all of the residual non-autistic individuals could owe their social skills and reproductive advantages to the same autism genes. Importantly, the reported modest correlations between core autistic dimensions can be illustrated using unsynchronized epistatic pleiotropy.

The neurobiology of autism

Improving clinical tests are allowing us to more precisely classify autism spectrum disorders and diagnose them at earlier ages. This raises the possibility of earlier and potentially more effective therapeutic interventions. To fully capitalize on this opportunity, however, will require better understanding of the neurobiological changes underlying this devastating group of developmental disorders. It is becoming clear that the normal trajectory of neurodevelopment is altered in autism, with aberrations in brain growth, neuronal patterning and cortical connectivity. Changes to the structure and function of synapses and dendrites have also been strongly implicated in the pathology of autism by morphological, genetic and animal modeling studies. Finally, environmental factors are likely to interact with the underlying genetic profile, and foster the clinical heterogeneity seen in autism spectrum disorders. In this review we attempt to link the molecular pathways altered in autism to the neurodevelopmental and clinical changes that characterize the disease. We focus on signaling molecules such as neurotrophin, Reelin, PTEN and hepatocyte growth factor, neurotransmitters such as serotonin and glutamate, and synaptic proteins such as neurexin, SHANK and neuroligin. We also discuss evidence implicating oxidative stress, neuroglial activation and neuroimmunity in autism.

Gene expression changes in children with autism

The objective of this study was to identify gene expression differences in blood differences in children with autism (AU) and autism spectrum disorder (ASD) compared to general population controls. Transcriptional profiles were compared with age- and gender-matched, typically developing children from the general population (GP). The AU group was subdivided based on a history of developmental regression (A-R) or a history of early onset (A-E without regression). Total RNA from blood was processed on human Affymetrix microarrays. Thirty-five children with AU (17 with early onset autism and 18 with autism with regression) and 14 ASD children (who did not meet criteria for AU) were compared to 12 GP children. Unpaired t tests (corrected for multiple comparisons with a false discovery rate of 0.05) detected a number of genes that were regulated more than 1.5-fold for AU versus GP (n=55 genes), for A-E versus GP (n=140 genes), for A-R versus GP (n=20 genes), and for A-R versus A-E (n=494 genes). No genes were significantly regulated for ASD versus GP. There were 11 genes shared between the comparisons of all autism subgroups to GP (AU, A-E, and A-R versus GP) and these genes were all expressed in natural killer cells and many belonged to the KEGG natural killer cytotoxicity pathway (p=0.02). A subset of these genes (n=7) was tested with qRT-PCR and all genes were found to be differentially expressed (p<0.05). We conclude that the gene expression data support emerging evidence for abnormalities in peripheral blood leukocytes in autism that could represent a genetic and/or environmental predisposition to the disorder.

Elevated NMDA receptor levels and enhanced postsynaptic long-term potentiation induced by prenatal exposure to valproic acid

Valproic acid (VPA) is a powerful teratogen causing birth defects in humans, including autism spectrum disorder (ASD), if exposure occurs during the first trimester of embryogenesis. Learning and memory alterations are common symptoms of ASD, but underlying molecular and synaptic alterations remain unknown. We therefore studied plasticity-related mechanisms in the neocortex of 2-week-old rats prenatally exposed to VPA and tested for changes in glutamate-mediated transmission and plasticity in the neocortex. We found a selective overexpression of NR2A and NR2B subunits of NMDA receptors, as well as the commonly linked kinase calcium/calmodulin-dependent protein kinase II. Synaptic plasticity experiments between pairs of pyramidal neurons revealed an augmented postsynaptic form of long-term potentiation. These results indicate that VPA significantly enhances NMDA receptor-mediated transmission and causes increased plasticity in the neocortex. Enhanced plasticity introduces a surprising perspective to the potential molecular and synaptic mechanisms involved in children prenatally exposed to VPA.

Family-based association study between GRIK2 polymorphisms and autism spectrum disorders in the Korean trios

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with strong genetic components. The present study comprises the detection of four single nucleotide polymorphisms (SNPs) in GRIK2 followed by a family-based association analysis of the SNPs in 126 Korean ASD trios by using the transmission disequilibrium test (TDT) and haplotype analysis. We found preferential transmission of the C allele at the rs3213607 (P<0.001) of GRIK2 in ASD and haplotype analysis revealed that one haplotype demonstrated a significant association (P=0.023). These results suggest a potential association between GRIK2 and ASD in the Korean population.

Decreased GAD67 mRNA levels in cerebellar Purkinje cells in autism: pathophysiological implications

The recent identification of decreased protein levels of glutamate decarboxylase (GAD) 65 and 67 isoforms in the autistic cerebellar tissue raises the possibility that abnormal regulation of GABA production in individual neurons may contribute to the clinical features of autism. Reductions in Purkinje cell number have been widely reported in autism. It is not known whether the GAD changes also occur in Purkinje cells at the level of transcription. Using a novel approach, the present study quantified GAD67 mRNA, the most abundant isoform in Purkinje cells, using in situ hybridization in adult autistic and control cases. The results indicate that GAD67 mRNA level was reduced by 40% in the autistic group (P < 0.0001; two-tailed t test), suggesting that reduced Purkinje cell GABA input to the cerebellar nuclei potentially disrupts cerebellar output to higher association cortices affecting motor and/or cognitive function. These findings may also contribute to the understanding of previous reports of alterations in the GABAergic system in limbic and cerebro-cortical areas contributing to a more widespread pathophysiology in autistic brains.

Relationship of dietary intake to gastrointestinal symptoms in children with autistic spectrum disorders

BACKGROUND

Gastrointestinal (GI) symptoms and abnormalities in stool consistency are frequently reported by parents of children with autism spectrum disorders (ASD). The purpose of this study was to 1) describe dietary intake of a cohort of children with ASD compared with normative data and 2) determine whether GI symptoms and stool consistency are related to dietary intake.

METHODS

Data from diet diaries of children (3-8 years) with ASD (n = 62) were analyzed by a registered pediatric dietician to compare to RDA standards for total calories, protein, carbohydrate, and fat. Dietary intake was correlated with descriptors of stool consistency using cumulative logistic regression methods.

RESULTS

Intake of calories, carbohydrates, and fat were in the average range; protein intake was increased (211% of RDA). Reported frequency of GI abnormalities, including abnormal stool consistency (e.g., bulky or loose), was increased (54%). No statistically significant relationships between stool consistency and dietary intake were observed.

CONCLUSIONS

In this sample, there was a high rate of reported gastrointestinal symptoms, despite lack of medical causes. Intake was adequate for calories and carbohydrates and increased for protein. The children did not exhibit excessive carbohydrate intake. There was no association of nutrient intake to changes in stool consistency.

Effect of pioglitazone treatment on behavioral symptoms in autistic children

Introduction

Autism is complex neuro-developmental disorder which has a symptomatic diagnosis in patients characterized by disorders in language/communication, behavior, and social interactions. The exact causes for autism are largely unknown, but is has been speculated that immune and inflammatory responses, particularly those of Th2 type, may be involved. Thiazolidinediones (TZDs) are agonists of the peroxisome proliferator activated receptor gamma (PPARγ), a nuclear hormone receptor which modulates insulin sensitivity, and have been shown to induce apoptosis in activated T-lymphocytes and exert anti-inflammatory effects in glial cells. The TZD pioglitazone (Actos) is an FDA-approved PPARγ agonist used to treat type 2 diabetes, with a good safety profile, currently being tested in clinical trials of other neurological diseases including AD and MS. We therefore tested the safety and therapeutic potential of oral pioglitazone in a small cohort of children with diagnosed autism.

Case description

The rationale and risks of taking pioglitazone were explained to the parents, consent was obtained, and treatment was initiated at either 30 or 60 mg per day p.o. A total of 25 children (average age 7.9 ± 0.7 year old) were enrolled. Safety was assessed by measurements of metabolic profiles and blood pressure; effects on behavioral symptoms were assessed by the Aberrant Behavior Checklist (ABC), which measures hyperactivity, inappropriate speech, irritability, lethargy, and stereotypy, done at baseline and after 3–4 months of treatment.

Discussion and evaluation

In a small cohort of autistic children, daily treatment with 30 or 60 mg p.o. pioglitazone for 3–4 months induced apparent clinical improvement without adverse events. There were no adverse effects noted and behavioral measurements revealed a significant decrease in 4 out of 5 subcategories (irritability, lethargy, stereotypy, and hyperactivity). Improved behaviors were inversely correlated with patient age, indicating stronger effects on the younger patients.

Conclusion

Pioglitazone should be considered for further testing of therapeutic potential in autistic patients.

Parental Recognition of Developmental Problems in Toddlers with Autism Spectrum Disorders

Symptoms of Autism Spectrum Disorders (ASD) begin to manifest during the first 2 years; there is limited evidence regarding type and timing of symptom onset. We examined factors related to parental age of recognition (AOR) of early abnormalities and the association between AOR and diagnosis and levels of functioning at 2 and 4 years in 75 toddlers with ASD. Results suggest significant differences between autism and PDD-NOS in the AOR and type of first concerns. Early social and motor delays as well as maternal age was associated with AOR. Later AOR was associated with poorer social-communicative and nonverbal cognitive functioning at 2 and 4. The findings are discussed in a context of identifying distinct developmental trajectories within the autism spectrum.

Adults with autism show increased sensitivity to outcomes at low error rates during decision-making

Decision-making is an important function that can be quantified using a two-choice prediction task. Individuals with Autistic Disorder (AD) often show highly restricted and repetitive behavior that may interfere with adaptive decision-making. We assessed whether AD adults showed repetitive behavior on the choice task that was unaffected by changing task demands, by examining the influence of experimenter-determined error rates on decision-making. Sixteen AD adults and 14 typically developed subjects were administered a two-choice task using three error rate conditions. Although AD subjects showed occurrences of stereotyped responding, their decision-making behavior was strongly affected by changes in task demands, especially when they experienced frequent success. Thus, behavioral paradigms that provide frequent reinforcement may be helpful in modifying decision-making abilities in AD.

Medical investigation of children with autistic spectrum disorders

Few well-constructed studies have systematically evaluated medical investigation protocols for children with autistic spectrum disorders. This is in large part due to the heterogeneous nature of the population and changing diagnostic frameworks. This review outlines the studies that have directed investigation strategies to date, and discusses how these might be applied in the clinical situation. The importance of listing the conditions that may be present on the basis of the specific clinical presentation, and using a thorough history and examination to generate a pre-test probability of the target disorders is emphasized if tests are to be useful in directing therapy or broader management approaches.

[Autism: neuroimaging]

Autism is a neurodevelopmental disorder with a range of clinical presentations. These presentations vary from mild to severe and are referred to as autism spectrum disorders. The most common clinical sign of autism spectrum disorders is social interaction impairment, which is associated with verbal and non-verbal communication deficits and stereotyped and repetitive behaviors. Thanks to recent brain imaging studies, scientists are getting a better idea of the neural circuits involved in autism spectrum disorders. Indeed, functional brain imaging, such as positron emission tomography, single foton emission tomography and functional MRI have opened a new perspective to study normal and pathological brain functioning. Three independent studies have found anatomical and rest functional temporal lobe abnormalities in autistic patients. These alterations are localized in the superior temporal sulcus bilaterally, an area which is critical for perception of key social stimuli. In addition, functional studies have shown hypoactivation of most areas implicated in social perception (face and voice perception) and social cognition (theory of mind). These data suggest an abnormal functioning of the social brain network in autism. The understanding of the functional alterations of this important mechanism may drive the elaboration of new and more adequate social re-educative strategies for autistic patients.

Familial Autoimmune Thyroid Disease as a Risk Factor for Regression in Children with Autism Spectrum Disorder: A CPEA Study

A multicenter study of 308 children with Autism Spectrum Disorder (ASD) was conducted through the Collaborative Programs of Excellence in Autism (CPEA), sponsored by the National Institute of Child Health and Human Development, to compare the family history of autoimmune disorders in children with ASD with and without a history of regression. A history of regression was determined from the results of the Autism Diagnostic Interview-Revised (ADI-R). Family history of autoimmune disorders was obtained by telephone interview. Regression was significantly associated with a family history of autoimmune disorders (adjusted OR=1.89; 95% CI: 1.17, 3.10). The only specific autoimmune disorder found to be associated with regression was autoimmune thyroid disease (adjusted OR=2.09; 95% CI: 1.28, 3.41).

Immunity, neuroglia and neuroinflammation in autism

Autism is a complex neurodevelopmental disorder of early onset that is highly variable in its clinical presentation. Although the causes of autism in most patients remain unknown, several lines of research support the view that both genetic and environmental factors influence the development of abnormal cortical circuitry that underlies autistic cognitive processes and behaviors. The role of the immune system in the development of autism is controversial. Several studies showing peripheral immune abnormalities support immune hypotheses, however until recently there have been no immune findings in the CNS. We recently demonstrated the presence of neuroglial and innate neuroimmune system activation in brain tissue and cerebrospinal fluid of patients with autism, findings that support the view that neuroimmune abnormalities occur in the brain of autistic patients and may contribute to the diversity of the autistic phenotypes. The role of neuroglial activation and neuroinflammation are still uncertain but could be critical in maintaining, if not also in initiating, some of the CNS abnormalities present in autism. A better understanding of the role of neuroinflammation in the pathogenesis of autism may have important clinical and therapeutic implications.

Analysis of four DLX homeobox genes in autistic probands

BACKGROUND

Linkage studies in autism have identified susceptibility loci on chromosomes 2q and 7q, regions containing the DLX1/2 and DLX5/6 bigene clusters. The DLX genes encode homeodomain transcription factors that control craniofacial patterning and differentiation and survival of forebrain inhibitory neurons. We investigated the role that sequence variants in DLX genes play in autism by in-depth resequencing of these genes in 161 autism probands from the AGRE collection.

RESULTS

Sequencing of exons, exon/intron boundaries and known enhancers of DLX1, 2, 5 and 6 identified several nonsynonymous variants in DLX2 and DLX5 and a variant in a DLX5/6 intragenic enhancer. The nonsynonymous variants were detected in 4 of 95 families from which samples were sequenced. Two of these four SNPs were not observed in 378 undiagnosed samples from North American populations, while the remaining 2 were seen in one sample each.

CONCLUSION

Segregation of these variants in pedigrees did not generally support a contribution to autism susceptibility by these genes, although functional analyses may provide insight into the biological understanding of these important proteins.

The human secretin gene in children with autistic spectrum disorder: screening for polymorphisms and mutations

We screened 29 children with autism for mutation in the human secretin gene using single-strand conformation polymorphism. No mutation was detected in exon 2, 3, or 4. Polymerase chain reaction and DNA sequence of 5' variable number of tandem repeats showed two polymorphisms with deletion or duplication of a repeat unit that failed to show any gene expression with transient transfection assay. We did not find evidence of a relationship between human secretin gene mutation and autism.

Parental perception of sleep problems in children of normal intelligence with pervasive developmental disorders: prevalence, severity, and pattern

OBJECTIVE

This study compares parents' perceptions of the prevalence, severity, and pattern of sleep problems in children of normal intelligence with pervasive developmental disorders (PDDs) with a normative comparison group of children.

METHOD

A survey including the Children's Sleep Habits Questionnaire was mailed to a sample of parents of children (age range 5-12 years) with PDDs (diagnosed by the Autism Diagnostic Interview-Revised) obtained by chart review of the past 7 years and to parents of comparison children matched on age, gender, and postal code.

RESULTS

The response rate in the PDD group was 82.2% (37/45) and 55.8% (43/77) in the comparison group. By individually matching, 23 pairs were obtained. The prevalence of sleep problems in the PDD group was reported by parents as being significantly higher than in the comparison group (78% and 26%, respectively; p < .002), as was the severity (mean score 48.2 and 39.0, respectively; p < .001). Values for four of eight sleep subscales including sleep onset delay, sleep duration, sleep anxiety, and parasomnias were significantly higher in the PDD group.

CONCLUSIONS

Parents report that sleep problems are significantly more prevalent and severe in children of normal intelligence with PDDs compared with normally developing children, and the pattern appears diverse. Sleep problems in children with PDDs require further research and clinical attention.

Early regression in social communication in autism spectrum disorders: a CPEA Study

In a multisite study of 351 children with autism spectrum disorders, 21 children with developmental delays, and 31 children with typical development, this study used caregiver interviews (i.e., the Autism Diagnostic Interview-Revised) at the time of entry into other research projects and follow-up telephone interviews designed for this project to describe the children's early acquisition and loss of social-communication milestones. Children who had used words spontaneously and meaningfully and then stopped talking were described by their caregivers as showing more gestures, greater participation in social games, and better receptive language before the loss and fewer of these skills after the loss than other children with autism spectrum disorders. A significant minority of children with autism without word loss showed a very similar pattern of loss of social-communication skills, a pattern not observed in the children with developmental delays or typical development.

Variation in Early Developmental Course in Autism and its Relation with Behavioral Outcome at 3–4 Years of Age

The aims of the present study were to describe variations in the early course of development in autism by utilizing an in-depth parent interview that incorporated techniques to improve accuracy of parent recall, and to examine the relation between variations in early developmental course in autism and behavioral outcome at 3-4 years of age. The Early Development Interview, which consisted of questions about child's behavior in several domains from birth through 2 years of age, was created and administered to parents of 72 3-4-year-old children with autism spectrum disorder and 34 3-4-year-old children with developmental delay, who were matched on mental and chronological age, and 39 1-4-year-old typically developing children, who were matched to the clinical groups on mental age. At 3-4 years of age, children were administered standardized measures (some clinician administered and some parent report); these included verbal and nonverbal IQ, autism symptom severity, and adaptive and aberrant behavior. Based on the Early Development Interview, children with autism spectrum disorder (ASD) were reported to have elevated symptoms in the social and regulatory domains by 3-6 months. By 12-15 months, parents of children with ASD reported significantly higher levels of social symptoms than parents of children with developmental delay. At 3-4 years of age, children with autism with early vs. late onset of symptoms, and with vs. without a history of loss of skills (regression) were not found to differ on standardized tests of verbal and nonverbal IQ and observational measures of autism symptom severity.

Reduced functional connectivity between V1 and inferior frontal cortex associated with visuomotor performance in autism

Some recent evidence has suggested abnormalities of the dorsal stream and possibly the mirror neuron system in autism, which may be responsible for impairments of joint attention, imitation, and secondarily for language delays. The current study investigates functional connectivity along the dorsal stream in autism, examining interregional blood oxygenation level dependent (BOLD) signal cross-correlation during visuomotor coordination. Eight high-functioning autistic men and eight handedness and age-matched controls were included. Visually prompted button presses were performed with the preferred hand. For each subject, functional connectivity was computed in terms of BOLD signal correlation with the mean time series in bilateral visual area 17. Our hypothesis of reduced dorsal stream connectivity in autism was only in part confirmed. Functional connectivity with superior parietal areas was not significantly reduced. However, the autism group showed significantly reduced connectivity with bilateral inferior frontal area 44, which is compatible with the hypothesis of mirror neuron defects in autism. More generally, our findings suggest that dorsal stream connectivity in autism may not be fully functional.

A “deficient environment” in prenatal life may compromise systems important for cognitive function by affecting BDNF in the hippocampus

The intrauterine environment has the capacity to mold the prenatal nervous system. Particularly, recent findings show that an adverse prenatal environment produces structural defects of the hippocampus, a critical area sub-serving learning and memory functions. These structural changes are accompanied by a disruption in the normal expression pattern of brain-derived neurotrophic factor (BDNF) and its cognate tyrosine kinase B (TrkB) receptor. The important role that the BDNF system plays in neural modeling and learning and memory processes suggests that fetal exposure to unfavorable intrauterine conditions may compromise proper cognitive function in adult life. These findings have implications for disorders that involve a dysfunction in the BDNF system and are accompanied by cognitive deficits.

Neuroglial activation and neuroinflammation in the brain of patients with autism

Autism is a neurodevelopmental disorder characterized by impaired communication and social interaction and may be accompanied by mental retardation and epilepsy. Its cause remains unknown, despite evidence that genetic, environmental, and immunological factors may play a role in its pathogenesis. To investigate whether immune-mediated mechanisms are involved in the pathogenesis of autism, we used immunocytochemistry, cytokine protein arrays, and enzyme-linked immunosorbent assays to study brain tissues and cerebrospinal fluid (CSF) from autistic patients and determined the magnitude of neuroglial and inflammatory reactions and their cytokine expression profiles. Brain tissues from cerebellum, midfrontal, and cingulate gyrus obtained at autopsy from 11 patients with autism were used for morphological studies. Fresh-frozen tissues available from seven patients and CSF from six living autistic patients were used for cytokine protein profiling. We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients. Immunocytochemical studies showed marked activation of microglia and astroglia, and cytokine profiling indicated that macrophage chemoattractant protein (MCP)-1 and tumor growth factor-beta1, derived from neuroglia, were the most prevalent cytokines in brain tissues. CSF showed a unique proinflammatory profile of cytokines, including a marked increase in MCP-1. Our findings indicate that innate neuroimmune reactions play a pathogenic role in an undefined proportion of autistic patients, suggesting that future therapies might involve modifying neuroglial responses in the brain.

Ontogeny of feline temporal lobe epilepsy in amygdala-kindled kittens: an update

This report describes amygdala-kindled seizure development and the post-kindling course in 58 cats (29 males and 29 females), including 40 preadolescents between 2.5 and 6.5 months of age and 18 adults >1 year of age at the beginning of kindling. The results extend previous findings, as follows: (1) Youngest animals (<5.0 months, n=30) are far more likely than older kittens and adults to exhibit spontaneous epilepsy, indexed by seizures that occur >1 h after stimulus-evoked seizures. (2) The youngest animals also exhibit accelerated kindling rates and rapid post-kindling onset of multifocal spontaneous epilepsy with a catastrophic clinical course. The profile includes a variety of EEG and/or clinical seizure manifestations and a progressive increase in the number and density of convulsive seizure clusters. Behavioral sequelae accompany seizure clusters and can range from sensory or motor deficits (visual agnosia, sensory hypersensitivity, atonic episodes, restricted mobility) to social isolation and placidity. (3) Onset of spontaneous epilepsy with developmental deterioration is substantially enhanced by recurrent evoked seizures early in the post-kindling course. The post-kindling progression can be stopped or minimized by suspension of evoked seizure trials and/or by management of frequent spontaneous convulsions (>1 per hour) with anticonvulsants. (4) In older cats, many more evoked seizures are required to generate fewer spontaneous seizures with relatively innocuous behavioral disorders. The findings suggest a 'critical period' in kindled kittens for onset of spontaneous temporal lobe epilepsy with severe behavioral consequences and a favorable prognosis for the young following early detection and intervention.

Expression and spatial distribution of secretin and secretin receptor in human cerebellum

The expression and spatial distribution of secretin and its receptor in human cerebellum were investigated by in situ hybridization and immunohistochemical techniques. Secretin mRNAs are found in Purkinje cells whereas secretin receptor transcripts are present in Purkinje cells and basket cells in the molecular cell layer. In addition, secretin-immunoreactivities are localized in both the soma and dendrites of Purkinje cells. These data are the first demonstration of the spatial distribution of secretin and its receptor in distinct neurons within the human cerebellum. The cellular localizations of this ligand-receptor pair are consistent with the proposed actions of secretin in the cerebellum of rodents and hence suggest that secretin also serves specific neural functions in the human cerebellum.

Cortical auditory evoked potentials in autism: a review

The question of etiology in autism remains elusive primarily due to the fact that autism does not result from a single dysfunction but is multi-faceted in nature. Investigations into etiology have ranged from identifying abnormalities in the genome to describing structural/functional brain abnormalities. Bearing in mind the risk of over-simplification, there is still utility in isolating a specific deficit to examine its etiologic contribution. It is known that individuals with autism have difficulty processing auditory information at the cortical level but this is not consistently seen subcortically. In recent years, cortical auditory processing has been extensively researched using event-related potentials (ERPs); however, these results in relation to autism have not been reviewed. This paper will examine this literature and discuss implications for future research.

Mutation screening and association study of the UBE2H gene on chromosome 7q32 in autistic disorder

Autistic disorder is a severe neurodevelopmental disorder most probably caused by a complex interaction of genetic factors. Several genomewide scans identified multipoint LOD score peaks in region 7q32. In this region, UBE2H encodes an E2 enzyme of the ubiquitin-dependent proteolytic system. Mutations in another member of this system, the UBE3A gene, cause Angelman syndrome. The participation of E2 (ubiquitin-conjugating enzymes) or E3 (ubiquitin ligases) enzymes in neural development recently emerged. Given its physical location and function, we examined UBE2H as a candidate for involvement in autistic disorder. We confirmed by reverse transcription-polymerase chain reaction that the UBE2H gene was expressed in the rat and the human central nervous system. The rat UBE2H and human UBE2H deduced amino acid sequences are identical. We screened the seven exons of the UBE2H gene in autistic patients using single-strand conformation analysis. We observed a silent A-->G transition at position 336. A case-control association study was performed using this A/G polymorphism. A significant association was found between the G allele and a subgroup of autistic patients with developmental quotient higher than 30 (P=0.004). Although further studies are required, these results suggest that the UBE2H gene could be one of the 7q-susceptibility loci for autistic disorder.

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.

Depletion of MAP2 expression and laminar cytoarchitectonic changes in dorsolateral prefrontal cortex in adult autistic individuals

The neuropathological substrates underlying the characteristic clinical phenotype of autism are unknown. Neuroimaging studies have identified a decrease in task-related activation in the dorsolateral prefrontal cortex in autism. In the current study, we have analysed the dorsolateral prefrontal cortex in two adult individuals with a clinical diagnosis of autism, using Nissl staining and MAP2 immunohistochemistry. There was unchanged density of both neuronal and glial cell pools, although the autistic individuals had ill-defined neocortical cellular layers, substantially depleted MAP2 neuronal expression, and reduced dendrite numbers. Further studies on a larger number of individuals with autism are needed to establish the clinical relevance of the described changes, especially to determine whether the loss of dendritic markers is age associated or disease specific.

Language and other regression: assessment and timing

Understanding of regression in autism has been hampered by variability in parental and clinical recognition and reporting of lost skills. This study introduced an instrument, the Regression Supplement Form, intended to supplement the Autism Diagnosis Interview-Revised and yield precise information about the types and timing of regression and events concurrent with loss and regain of skills. Data were collected from parents of 44 children (38 male, 6 female; mean age = 6 years) with Autistic Spectrum Disorder (37 Autistic Disorder, 7 Pervasive Developmental Disorder-Not Otherwise Specified). Parental responses on the Autism Diagnosis Interview-Revised indicated loss of skills during early development. The profile of regression that emerged included loss of skills between 18 and 21 months, on average, with language-only regression less common than loss of other, nonlanguage skills only or of full regression (loss of language and other skills). The onset of regression typically was gradual in nonlanguage areas and split between gradual and sudden loss for language skills. Some of the children were developing atypically before they lost other, nonlanguage skills, that is, their age at first words was delayed until age 2 years or older. Parents tended to attribute loss to medical factors such as immunizations. Many of the children regained some of the lost skills when they were 3.5-5 years of age, with therapeutic and instructional interventions given credit for the regain.

Alteration in amino-glycerophospholipids levels in the plasma of children with autism: a potential biochemical diagnostic marker

Currently, there is no biochemical test to assist in the behavioral diagnosis of autism. We observed that levels of phosphatidylethanolamine (PE) were decreased while phosphatidylserine (PS) were increased in the erythrocyte membranes of children with autism as compared to their non-autistic developmentally normal siblings. A new method using Trinitrobenezene sulfonic acid (TNBS) for the quantification of PE and PS (amino-glycerophospholipids, i.e., AGP) in the plasma of children was developed and standardized. Wavelength scans of TNBS-PE and TNBS-PS complexes gave two peaks at 320 nm and 410 nm. When varying concentrations of PS and PE were used, a linear regression line was observed at 410 nm with TNBS. Using this assay, the levels of AGP were found to be significantly increased in the plasma of children with autism as compared to their non-autistic normal siblings. It is proposed that plasma AGP levels may function as a potential diagnostic marker for autism.

Linkage analysis for autism in a subset families with obsessive-compulsive behaviors: evidence for an autism susceptibility gene on chromosome 1 and further support for susceptibility genes on chromosome 6 and 19

Although there is considerable evidence for a strong genetic component to idiopathic autism, several genome-wide screens for susceptibility genes have been carried out with limited concordance of linked loci, reflecting numerous genes of weak effect and/or sample heterogeneity. In the current study, linkage analysis was carried out in a sample of 62 autism-affected relative pairs with more severe obsessive-compulsive behaviors, selected from a larger (n=115) set of autism-affected relative pairs as a means of reducing sample heterogeneity. Obsessive-compulsive behaviors were assessed using the Autism Diagnostic Interview-Revised (ADI-R). In the sample with more severe obsessive-compulsive behaviors, multipoint NPL scores above 2 were observed on chromosomes 1, 4, 5, 6, 10, 11 and 19, with the strongest evidence for linkage on chromosome 1 at the marker D1S1656, where the multipoint NPL score was 3.06, and the two-point NPL score was 3.21. In follow-up analyses, analyzing the subset of families (n=35) where the patients had the most severe obsessive-compulsive behaviors generated a multipoint NPL score of 2.76, and a two-point NPL score of 2.79, indicating that the bulk of evidence for linkage was derived from the families most severely affected with obsessive-compulsive behaviors. The data suggest that there is an autism susceptibility gene on chromosome 1 and provide further support for the presence of autism susceptibility genes on chromosomes 6 and 19.

The prenatal autistic imprinting hypothesis: developmental maladaptation to the environmental changes between womb and the social world

Although the importance of biological and genetic aspects of the etiology is well recognized, the pathological process of autism still remains to be elucidated. In contrast to a qualitative dichotomy concept, a dimensional perspective that places the autistic traits as quantitative extremes can easily explain the diversity and subtlety of the clinical features. In a dimensional (quantitative continuum) condition, no single qualitative process can distinguish the extremes from normal variations. In addition, the traditional view, which regards autism as a hypo-reproductive disease with a strong genetic contribution, cannot interpret the recent worldwide prevalence of autism. From a novel viewpoint, we have proposed 'the prenatal autistic imprinting hypothesis' in which autism is regarded as an inevitable consequence of human social evolution in both past and future. Postulated primary phenotypes are closely associated with the autistic savant skills and the autistic adherent temperament, and might increase the chance of specific prenatal experiences, named 'autistic imprinting'. An earlier prenatal brain growth and an earlier establishment of a type of consciousness may be critical for the imprinting process. A postnatal autistic social maladaptation may be a mere outcome of the putative intrauterine behavioral adaptation in individuals with the primary phenotypes. Both an autistic manner of thinking, which is referred to as 'visual thinking', and the prenatal early development of visual cortical architectures may play a key role in the autistic imprinting process.

Neonatal Amygdala Lesions and Juvenile Isolation in the Rat: Differential Effects on Locomotor and Social Behavior Later in Life

Pervasive developmental disorders such as autism are characterized by deficits in social interaction and communication. Disturbed development of limbic structures such as the amygdala might underlie these deficits. The authors examined the effects of amygdala lesions on Postnatal Day 7 and juvenile isolation (2 weeks of individual housing during Weeks 4 and 5 of life) on rat locomotor and social activity later in life. Before puberty, but more pronounced after puberty, lesioned rats displayed enhanced locomotor activity. Adult social behavior was selectively disturbed by the lesion and the isolation procedure. In particular, the combination of neonatal lesions and juvenile isolation severely disrupted social interaction. These results suggest that a combination of neonatal amygdala damage and juvenile isolation may serve as an animal model of certain psychopathological neurodevelopmental disorders, such as autism.

Sleep and arousal mechanisms in experimental epilepsy: Epileptic components of NREM and antiepileptic components of REM sleep

Neural generators related to different sleep components have different effects on seizure discharge. These sleep-related systems can provoke seizure discharge propagation during nonrapid eye movement (NREM) sleep and can suppress propagation during REM sleep. Experimental manipulations of discrete physiological components were conducted in feline epilepsy models, mostly in the systemic penicillin epilepsy model of primary generalized epilepsy and the amygdala kindling model of the localization-related seizure disorder, temporal lobe epilepsy. The sleep-wake state distribution of seizures was quantified before and after discrete lesions, systemic and localized drug administration, and/or photic stimulation, as well as in relation to microdialysis of norepinephrine. We found that (1) neural generators of synchronous EEG oscillations--including tonic background slow waves and phasic "arousal" events (sleep EEG transients such as sleep spindles and k-complexes)--combine to promote electrographic seizure propagation during NREM and drowsiness, and antigravity muscle tone permits seizure-related movement; (2) neural generators of asynchronous neuronal discharge patterns reduce electrographic seizures during alert waking and REM sleep, and skeletal motor paralysis blocks seizure-related movement during REM; (3) there are a number of similarities between amygdala-kindled kittens and children with Landau-Kleffner Syndrome (LKS) that suggest a link among seizures, sleep disorders, and behavioral abnormalities/regression.

Model of autism: increased ratio of excitation/inhibition in key neural systems

Autism is a severe neurobehavioral syndrome, arising largely as an inherited disorder, which can arise from several diseases. Despite recent advances in identifying some genes that can cause autism, its underlying neurological mechanisms are uncertain. Autism is best conceptualized by considering the neural systems that may be defective in autistic individuals. Recent advances in understanding neural systems that process sensory information, various types of memories and social and emotional behaviors are reviewed and compared with known abnormalities in autism. Then, specific genetic abnormalities that are linked with autism are examined. Synthesis of this information leads to a model that postulates that some forms of autism are caused by an increased ratio of excitation/inhibition in sensory, mnemonic, social and emotional systems. The model further postulates that the increased ratio of excitation/inhibition can be caused by combinatorial effects of genetic and environmental variables that impinge upon a given neural system. Furthermore, the model suggests potential therapeutic interventions.

Neurotrophic factors in the pathogenesis of Rett syndrome

Rett syndrome is characterized by disruption of a period of vigorous brain growth with synapse development. Neurotrophic factors are important regulators of neuronal growth, differentiation, and survival during early brain development. The aims of this study were to study the role of neurotrophic factors in Rett syndrome, specifically whether Rett syndrome has abnormal levels of specific neurotrophic factors in serum and cerebrospinal fluid and whether the changes differ from other neuropediatric patients, for example, those with infantile autism. Four neurotrophic factors were measured: nerve growth factor, brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and insulin-like growth factor 1 from the frozen cerebrospinal fluid and from serum (except glial cell line-derived neurotrophic factor) by enzyme-linked immunosorbent assay and cerebrospinal fluid glutamate and aspartate by high-performance liquid chromatography (HPLC) method in patients with Rett syndrome. Insulin-like growth factor 1 was measured from the cerebrospinal fluid of patients with infantile autism. We found low concentrations of cerebrospinal fluid nerve growth factor in patients with Rett syndrome compared with control patients. The serum levels and other cerebrospinal fluid neurotrophic factor levels of the patients did not differ from the controls. Patients with Rett syndrome had high cerebrospinal fluid glutamate levels. Patients with infantile autism had low cerebrospinal fluid insulin-like growth factor 1 levels. Nerve growth factor acts especially on cholinergic neurons of the basal forebrain, whereas insulin-like growth factor 1 acts on cerebellar neurons. In Rett syndrome, the forebrain is more severely affected than the other cortical areas. In autism, many studies show hippocampal or cerebellar pathology. Our findings are in agreement with the different morphologic and neurochemical findings (brain growth, affected brain areas, neurotransmitter metabolism) in the two syndromes. Impairment in dendritic development in Rett syndrome could be the consequence of cholinergic deficiency and of neurotrophic factor/glutamate imbalance. Cholinergic gene expression might be influenced by the Rett syndrome gene directly or via the neurotrophic factor system.

Molecular genetics of autism spectrum disorders

Autistic disorder belongs to a broad spectrum of pervasive developmental disorders. Autism is a clinically and genetically heterogeneous condition. It is characterized by impairment in a broad range of social interactions, communication, and repetitive patterns of behavior and interest. Although the exact etiology of the condition is not known, family and twin studies strongly support genetic factors in autism. Genome-wide scans suggest several susceptibility loci that may contain one or more predisposing genes. However, no such genes have been identified so far that predispose patients to autism. The condition is over 90% heritable, but the mode of inheritance is not clear. Moreover, it does not seem to be a single gene disorder. There is no cure for autism. Individualized structured education, family support services, and antipsychotic drugs are recommended. These may alleviate some behavioral problems. The identification of autism genes, an understanding of the neurobiology of the condition, and additional clinical studies may help to develop pharmacological interventions in the future.

Children with autistic spectrum disorders. II: parents are unable to distinguish secretin from placebo under double-blind conditions

BACKGROUND

Standardised measures of behaviour have failed to detect short term improvement in children with autism following treatment with secretin. However, it is possible that standardised measures are insensitive to dimensions of child behaviour that are nonetheless detectable by parents.

AIM

To determine the ability of parents of children with autism to guess, under double blind conditions, whether their child had received secretin or placebo.

METHODS

2x2 crossover randomised blinded study, comparing the effect of synthetic human secretin 2 U/kg to placebo (saline). Sixty two children with autism (aged 43-103 months) were randomly allocated to two groups: group 1 received placebo, followed six weeks later by secretin, and group 2 received secretin followed by placebo. At the conclusion of the study, parents were asked to guess their child's group assignment.

RESULTS

Twenty seven families guessed their child's group assignment correctly and 27 guessed incorrectly. In 48 instances, parents based their guess on perceived improvement; in six cases, parents based their guess on perceived deterioration. Six families saw no difference after either infusion, and offered no guess. One family dropped out after the first infusion, and one family was lost to follow up after the second infusion.

CONCLUSION

In a controlled setting, parents of young children with autism are unable to distinguish the short term behavioural effects of secretin from placebo.

Intestinal cytokines in children with pervasive developmental disorders

OBJECTIVES

A relationship between autism and gastrointestinal (GI) immune dysregulation has been postulated based on incidence of GI complaints as well as macroscopically observed lymphonodular hyperplasia and microscopically determined enterocolitis in pediatric patients with autism. To evaluate GI immunity, we quantitatively assessed levels of proinflammatory cytokines, interleukin (IL)-6, IL-8, and IL-1beta, produced by intestinal biopsies of children with pervasive developmental disorders.

METHODS

Fifteen patients, six with pervasive developmental disorders and nine age-matched controls, presenting for diagnostic colonoscopy were enrolled. Endoscopic biopsies were organ cultured, supernatants were harvested, and IL-6, IL-8, and IL-1beta levels were quantified by ELISA. Tissue histology was evaluated by blinded pathologists.

RESULTS

Concentrations of IL-6 from intestinal organ culture supernatants of patients with pervasive developmental disorders (median 318.5 pg/ml, interquartile range 282.0-393.0 pg/ml) when compared with controls (median 436.9 pg/ml, interquartile range 312.6-602.5 pg/ml) were not significantly different (p = 0.0987). Concentrations of IL-8 (median 84,000 pg/ml, interquartile range 16,000-143,000 pg/ml) when compared with controls (median 177,000 pg/ml, interquartile range 114,000-244,000 pg/ml) were not significantly different (p = 0.0707). Concentrations of IL-1beta (median 0.0 pg/ml, interquartile range 0.0-94.7 pg/ml) when compared with controls (median 0.0 pg/ml, interquartile range 0.0-60.2 pg/ml) were not significantly different (p = 0.8826). Tissue histology was nonpathological for all patients.

CONCLUSIONS

We have demonstrated no significant difference in production of IL-6, IL-8, and IL-1beta between patients with pervasive developmental disorders and age-matched controls. In general, intestinal levels of IL-6 and IL-8 were lower in patients with pervasive developmental disorders than in age-matched controls. These data fail to support an association between autism and GI inflammation.

Children with autistic spectrum disorders. I: comparison of placebo and single dose of human synthetic secretin

AIMS

To examine the effect of a single dose of human synthetic secretin (HSS) on behaviour and communication in children with autism spectrum disorder (ASD) using an objective measure of communication and social reciprocity and standardised rating scales.

METHODS

Randomised, crossover, double blind, and placebo controlled trial of a single intravenous dose of human synthetic secretin (HSS) 2 CU/kg. The 62 subjects (3-8 years) were assigned to group 1 (saline placebo/HSS) or group 2 (HSS/saline placebo). Diagnosis was confirmed by ADI-R (Autism Diagnostic Interview-Revised) algorithm. Severity of symptoms was rated using the CARS (Childhood Autism Rating Scale). Outcome measures included Communication and Symbolic Behavior Scale (CSBS), Ritvo Real-life Rating Scale, weekly Global Rating Scale (GBRS) by parents and teachers, and daily log of gastrointestinal symptoms. The communication subscale of the CSBS, specifying communication function, reciprocity, and social-affective signalling was videotaped and scored by a blinded, trained observer.

RESULTS

Sixty one children completed the study. After randomisation, there were no significant differences in gender, race, age, and parent and teacher GBRS and Ritvo Scale between the two groups. Compared with placebo, secretin treatment was not associated with significant improvement of CSBS standard scores from baseline to 2 or 4 weeks post-infusion. Five children showed clinical improvement in standard scores: two after HSS and three after placebo. There were no significant changes in gastrointestinal symptoms after HSS or saline placebo.

CONCLUSIONS

A single dose of intravenous human secretin is not effective in changing behaviour and communication in children with ASD when compared to placebo.

Maternal neuronal antibodies associated with autism and a language disorder

Neurodevelopmental disorders could be caused by maternal antibodies or other serum factors. We detected serum antibodies binding to rodent Purkinje cells and other neurons in a mother of three children: the first normal, the second with autism, and the third with a severe specific language disorder. We injected the serum (0.5-1.0 ml/day) into pregnant mice during gestation and found altered exploration and motor coordination and changes in cerebellar magnetic resonance spectroscopy in the mouse offspring, comparing with offspring of mice injected with sera from mothers of healthy children. This evidence supports a role for maternal antibodies in some forms of neurodevelopmental disorder.

Childhood autism: a circuit syndrome?

BACKGROUND

Autism is a disorder that can lead to life-long disability. Currently, the etiology of autism is unknown, and although there are treatments for some of the behavioral abnormalities, there is no cure.

REVIEW SUMMARY

While this article will review the clinical, anatomic, and pathologic features seen in autism, the primary focus will be to present a new and provocative unifying theory regarding the underlying mechanisms causing this disorder. Current research advances, some controversial, will be discussed, and a novel definition of autism as a "circuit syndrome" will be presented. The work elaborated here will tie many of the disparate findings together, based on the idea that autism arises from abnormalities of the cerebellolimbic circuitry. Some of the more alternative theories of autism, such as mercury toxicity, linkage to the measles, mumps, and rubella vaccine, and the use of secretin will be discussed. Finally, pharmacologic treatment options will be reviewed.

CONCLUSIONS

Autism is not single disorder but represents dysfunction of the cerebellolimbic circuitry that can arise from many different etiologies.

Sleep patterns of children with pervasive developmental disorders

Data on sleep behavior were gathered on 100 children with pervasive developmental disorders (PDD), ages 2-11 years, using sleep diaries, the Children's Sleep Habits Questionnaire (CSHQ), and the Parenting Events Questionnaire. Two time periods were sampled to assess short-term stability of sleep-wake patterns. Before data collection, slightly more than half of the parents, when queried, reported a sleep problem in their child. Subsequent diary and CSHQ reports confirmed more fragmented sleep in those children who were described by their parents as having a sleep problem compared to those without a designated problem. Interestingly, regardless of parental perception of problematic sleep, all children with PDD exhibited longer sleep onset times and greater fragmentation of sleep than that reported for age-matched community norms. The results demonstrate that sleep problems identified by the parent, as well as fragmentation of sleep patterns obtained from sleep diary and CSHQ data, exist in a significant proportion of children with PDD.

Epilepsy in autism

There is an increased but variable risk of epilepsy in autism. Three main factors--age, cognitive level, and type of language disorder--account for variability in the reported prevalence of epilepsy. The prevalence is highest in studies that have included adolescents and young adults, individuals with moderate to severe mental retardation and those with motor deficits, and individuals with severe receptive language deficits. The association of autism with clinical or subclinical epilepsy might denote common genetic factors in some cases. Whether subclinical epilepsy has adverse effects on cognition, language, and behaviour is debated, as is the relation of autistic regression with an epileptiform electroencephalogram to Landau-Kleffner syndrome. There is no evidence-based treatment recommendation for individuals with autism, regression, and subclinical epilepsy. Double-blind studies with sufficient power to resolve this issue are urgently needed.

Autism, macrocrania and epilepsy: how are they linked?

To evaluate the possible association of autistic disorder (AD), macrocrania and epilepsy, we performed a retrospective study comparing epileptic and non-epileptic AD patients with macrocrania, and AD patients with macrocrania to age- and sex-matched AD controls without macrocrania. We found macrocrania in 17.3% of 121 patients with AD. Epilepsy was not significantly more frequent in AD patients with macrocrania than in those without macrocrania. There were no significant differences in the other clinical characteristics studied except for epileptiform EEG abnormalities which were more often found in AD patients with epilepsy. AD with macrocrania and epilepsy is not a syndrome but may be a marker for a group of subjects with AD. A role for familial macrocrania needs further assessment.

The human secretin gene: fine structure in 11p15.5 and sequence variation in patients with autism

Secretin is a peptide hormone involved in digestion that has been studied as a potential therapeutic agent in patients with autism. We characterized the human secretin locus to determine whether mutations in this gene might play a role in a fraction of autism patients. While the secretin gene (SCT) was not found to be mutated in the majority of autistic patients, rare heterozygous sequence variants were identified in three patients. We also investigated length variation in a variable number of tandem repeats (VNTR) immediately upstream of SCT and found no significant differences in length between patients with autism and normal controls. SCT is located on 11p15.5, adjacent to DRD4 and HRAS. This region has been reported to be associated with both autism and attention deficit hyperactivity disorder (ADHD). Although imprinting is a characteristic of some genes in the vicinity, we could find no evidence for methylation of SCT in lymphoblast cells from patients or control individuals.