Elsevier

The Lancet

Volume 374, Issue 9701, 7–13 November 2009, Pages 1627-1638
The Lancet

Seminar
Autism

https://doi.org/10.1016/S0140-6736(09)61376-3Get rights and content

Summary

Autism spectrum disorders are characterised by severe deficits in socialisation, communication, and repetitive or unusual behaviours. Increases over time in the frequency of these disorders (to present rates of about 60 cases per 10 000 children) might be attributable to factors such as new administrative classifications, policy and practice changes, and increased awareness. Surveillance and screening strategies for early identification could enable early treatment and improved outcomes. Autism spectrum disorders are highly genetic and multifactorial, with many risk factors acting together. Genes that affect synaptic maturation are implicated, resulting in neurobiological theories focusing on connectivity and neural effects of gene expression. Several treatments might address core and comorbid symptoms. However, not all treatments have been adequately studied. Improved strategies for early identification with phenotypic characteristics and biological markers (eg, electrophysiological changes) might hopefully improve effectiveness of treatment. Further knowledge about early identification, neurobiology of autism, effective treatments, and the effect of this disorder on families is needed.

Introduction

Autism is a neurodevelopmental disorder in the category of pervasive developmental disorders, and is characterised by severe and pervasive impairment in reciprocal socialisation, qualitative impairment in communication, and repetitive or unusual behaviour. The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV)1 and the International Classification of Diseases, 10th edition (ICD-10),2 include autistic disorder, Asperger's syndrome, pervasive developmental disorder-not otherwise specified (PDD-NOS), Rett's syndrome, and childhood disintegrative disorder as pervasive developmental disorders. Clinicians and researchers use autism spectrum disorders to include autism, Asperger's syndrome, and PDD-NOS, which we discuss in this Seminar. For children with Rett's disorder or childhood disintegrative disorder, their clinical course, pathophysiology, and the diagnostic strategies used are different and are not addressed in this Seminar.

Section snippets

Epidemiology

We focus on prevalence of autism spectrum disorders and possible causes of changes in prevalence. Although estimates vary, prevalence seems to have increased greatly since the 1960s, when rates included only autistic disorder. In the 20 years since, in the USA and Europe prevalence rates ranged from five to 72 cases per 10 000 children.3, 4 These estimates were affected by screening, case-confirmation strategies, and sample size, with small sample sizes resulting in high estimates. Prevalence

Clinical characteristics and screening

Core symptoms of autism spectrum disorders affect domains of socialisation, communication, and behaviour (panel 1). Clinical signs are usually present by age 3 years, but typical language development might delay identification of symptoms. Results of prospective studies11 of infants at risk (ie, younger siblings of affected children) have shown that deficits in social responsiveness, communication, and play can be present in those as young as age 6–12 months. Diagnoses show heterogeneity of

Assessment

Children identified to be at risk should be referred for comprehensive developmental and diagnostic assessment for autism spectrum disorders. This assessment might be done through community resources (eg, early intervention staff, educators, psychologists, or speech pathologists), educational agencies, or local developmental clinicians. Reviews of early identification and screening are available.15, 17, 19 If concerns that a child has autism spectrum disorder are validated, comprehensive

Neurobiology

Attempts to identify unified theories explaining core and comorbid deficits have been unsuccessful, which is not surprising in view of the heterogeneous expression of autism spectrum disorders. In studies64 of this disorder as a neurodevelopmental disorder of prenatal and postnatal brain development, researchers have attempted to elucidate these theories by examination of brain growth, functional neural networks, neuropathology, electrophysiology, and neurochemistry. Neurocognitive theories

Causes

Autism spectrum disorder is highly genetic. The relative risk of a second child having this diagnosis is 20–50 times higher than the population base rate,71 and thus families should consider genetic counselling. Parents and siblings often show mild, subsyndromal manifestations of autism, the broad autism phenotype,72 including delayed language, difficulties with social aspects of language (pragmatics), delayed social development, absence of close friendships, and a perfectionistic or rigid

Genetics

Since 2003,12 fundamental changes in our understanding of the genetics of autism have taken place. Previously, this specialty was guided almost exclusively by the common disorder–common gene model,76 proposing that many genes frequently identified in the general population each confer small-to-moderate effects on the phenotype. Only a few common variants have been identified as possible candidate genes in linkage and association studies,77 and many of these have not been verified in subsequent

New developments

Advances in cognitive and affective developmental neuroscience, neurobiology, and the genetics of autism spectrum disorder have resulted in potentially novel methods for early detection and improved targeting and effectiveness of treatments.85 For example, neuroimaging strategies such as functional MRI and magnetoencephalography might provide biomarkers to monitor physiological changes before and after treatment. We still do not know which treatments or combinations of types of treatments will

Future directions

In the past 10 years,119 much progress has been made with diagnosis and management of autism spectrum disorder. Hopefully, early detection and diagnosis of infants and children at risk will enable treatments to be designed and implemented to alter the course of early behaviour and brain development.85 Amaral and colleagues120 suggested that the heterogeneity of factors affecting brain development predicts a heterogeneous pattern of neuropathology. Through neuroimaging approaches such as

Search strategy and selection criteria

We searched Medline, Psychinfo, and Cochrane Library databases from January, 1998, to December, 2008, with the search terms “autism”, “autistic disorder”, “pervasive developmental disorder”, “autism spectrum disorder”, and “Asperger syndrome” in combination with “evaluation”, “diagnosis”, “treatment”, “therapy”, “medication”, “pharmacotherapy”, “epidemiology”, “genetics”, “neuroimaging”, “behavior therapy”, “early identification”, “outcome”, and “complementary and alternative therapy.” We

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