Elsevier

The Lancet

Volume 392, Issue 10146, 11–17 August 2018, Pages 508-520
The Lancet

Seminar
Autism spectrum disorder

https://doi.org/10.1016/S0140-6736(18)31129-2Get rights and content

Summary

Autism spectrum disorder is a term used to describe a constellation of early-appearing social communication deficits and repetitive sensory–motor behaviours associated with a strong genetic component as well as other causes. The outlook for many individuals with autism spectrum disorder today is brighter than it was 50 years ago; more people with the condition are able to speak, read, and live in the community rather than in institutions, and some will be largely free from symptoms of the disorder by adulthood. Nevertheless, most individuals will not work full-time or live independently. Genetics and neuroscience have identified intriguing patterns of risk, but without much practical benefit yet. Considerable work is still needed to understand how and when behavioural and medical treatments can be effective, and for which children, including those with substantial comorbidities. It is also important to implement what we already know and develop services for adults with autism spectrum disorder. Clinicians can make a difference by providing timely and individualised help to families navigating referrals and access to community support systems, by providing accurate information despite often unfiltered media input, and by anticipating transitions such as family changes and school entry and leaving.

Introduction

In the past 50 years, autism spectrum disorder (ASD) has gone from a narrowly defined, rare disorder of childhood onset to a well publicised, advocated, and researched lifelong condition, recognised as fairly common and very heterogeneous. The description of the core features of ASD as being social communication deficits and repetitive and unusual sensory–motor behaviours has not changed substantially since its original delineation.1 However, autism is now seen as a spectrum that can range from very mild to severe. Nevertheless, many (but not all) individuals with ASD require lifelong support of some kind.

Although families, teachers, and direct providers make the most differences to the lives of people with ASD, physicians and other clinicians also affect individuals and families by providing information about the current functioning of the person with ASD, by helping caregivers to anticipate transitions, and by navigating referrals to service providers and specialists when needed. ASD represents a substantial economic burden, mainly due to the provision of support to adults who cannot function independently, which results in higher health-care and school costs and loss of income for caregivers.2 This Seminar focuses on summarising current research so that clinicians can provide guidance to families within the context of ASD, recognising that, although ASD is a biological disorder, it is primarily treated through education and behavioural services, with medication as an important adjunct.

Section snippets

Signs, symptoms, and general diagnostic issues

Although individuals with ASD are very different from one another, the disorder is characterised by core features in two areas—social communication and restricted, repetitive sensory–motor behaviours—irrespective of culture, race, ethnicity, or socioeconomic group.3 ASD results from early altered brain development and neural reorganisation.4, 5 However, because there are no reliable biomarkers, the diagnosis must be made on the basis of behaviour. The American Psychiatric Association's

Questions about screening

Issues related to screening and subsequent diagnosis, both for families and providers, are often different for very young children than for older children, adolescents, and adults, and therefore will be discussed separately. There are no data from well controlled studies about the extent to which early intervention changes adult outcomes, and it is generally not possible to measure the factors that predict later outcomes (eg, language development or cognitive level) at the ages proposed for

Early diagnosis

ASD can be diagnosed by various professionals (paediatricians, psychiatrists, or psychologists), ideally with input from multiple disciplines. Standardised diagnostic instruments are available, including the Screening Tool for Autism in Toddlers and Young Children (STAT; a 20-min observation for young children) and the more heavily researched Autism Diagnostic Observation Schedule (ADOS;16 a 45-min observation done by a skilled professional, available in different formats for people of

Diagnosis, ASD, and intellectual disability

One source of tension regarding the provision of straightforward and simple recommendations for ASD diagnosis and services is the heterogeneity across regions and ages in the association between ASD and intellectual disabilities. Because very young children with clear developmental disabilities are likely to receive referrals for treatment or specialist assessment earlier than those without, care should be taken not to overlook very verbal young children with ASD.21 Clear predictions of later

Diagnosis in older children and adolescents

For older children (ie, those in later primary school), adolescents, or adults whose families suspect that they might have ASD, questions about diagnosis are different because the individual often already has a history of difficulties.26 Even though the majority of children with ASD in northern Europe and North America are diagnosed by early school age, there remain others who have never had a diagnosis.27 Later diagnoses often occur in the context of co-occurring problems such as anxiety,

ASD in adulthood

Estimates vary, but 10–33% of adults with ASD do not use more than simple phrases and have verbal and non-verbal IQs in the range of intellectual disability, requiring very substantial support.21, 26, 31 Most adults with ASD with intellectual disability can speak at some level, can take care of basic needs, and have the ability to work, but need daily support. Premature mortality is increased, primarily in individuals with lower intellectual abilities and in women (mostly resulting from

Co-occurring psychiatric conditions in ASD

Clinicians have long been aware that ASD is often accompanied by other difficulties. In addition to ASD, the earliest considerations are usually developmental delay or intellectual disability, and language and motor difficulties. DSM-5 recognises this complexity by allowing multiple diagnoses, even within psychiatry, such as ASD and ADHD.

ADHD is the most common comorbidity in people with ASD (28·2% [95% CI 13·3–43·0]),42 and considerably affects outcomes in children with ASD who have average

Trajectories and predictors of outcome

The range of outcomes, from individuals who remain non-verbal to those able to work and live independently without continuing ASD symptoms, greatly increases uncertainty for families and pressure on parents to get the most out of each intervention. Diagnoses of ASD can be made in children as young as 15–24 months in some cases, although these early diagnoses should be monitored closely.47 The greatest gains, even into adulthood, are made by children who have begun to make progress in language

Descriptive epidemiology

A 2012 review commissioned by WHO estimated that the global prevalence of ASD was about 1%,50 with a more recent review estimating the prevalence to be 1·5% in developed countries.51 Increases in prevalence estimates in the USA over the past several decades have now mostly plateaued21 and probably can be largely accounted for by improved awareness and services, differences in documentation, and the inclusion of milder cases without intellectual disability.52 Only two rigorous studies of adult

Environmental risk factors

Many risk factors for ASD have been suggested. A number of systematic reviews and meta-analyses have described prenatal and perinatal factors, as well as maternal dietary and lifestyle factors.53 The immediate practical implications of most environmental factors for families hoping to minimise their risk with a subsequent child (after already having a child with ASD) are so far limited to the identification of likely-causal genetic anomalies in a minority of cases.

Advanced maternal age (≥40

ASD and paediatric conditions

ASD is strongly associated with numerous coexisting conditions—physical, mental, neurodevelopmental, and functional—that are not part of the diagnostic criteria but can nevertheless have a substantial, often negative, effect on the wellbeing of the child or young person and their family, and can require modification of intervention strategies. Coexisting conditions vary in prevalence depending on the population studied, but include other neurodevelopmental disorders, intellectual disability (IQ

Genetics

The past decade has seen a shift from a general concept of genetic risk to more specific attention to a large number of heterogeneous, individual genetic variants associated with ASD risk. The shifting definitions of ASD have led to variable rates of diagnosis in twin and family studies. A meta-analysis published in 2016 reported that 74–93% of ASD risk is heritable,75 although non-genetic factors are also important. Sibling studies indicate that ASD occurs in 7–20% of subsequent children after

Neurobiology

In neurobiology, ASD is no longer viewed as a focal impairment in a specific brain region or system, but instead as a condition resulting from overall brain reorganisation beginning early in development. Among the most well replicated findings is a pattern of overgrowth of brain volume in infancy and early childhood, as documented through differences in brain volume on neuroimaging.90, 91 Relative to typically developing children, those with ASD have accelerated brain development early in life,

Treatment

How much and what kind of intervention children and adults with ASD receive vary immensely across the world and even within countries and regions.94 One consistent finding across many (although not all) locations is that parents with a lower educational level are less successful in obtaining specialist interventions that could improve outcomes. In one survey about European services for less well educated families, even low-cost and publicly funded interventions were not available to children

Future directions

Given existing health systems, there are clear, continuing needs for coordination between health-care, education, and other services (such as intense support for challenging behaviours and planning for adult residential and employment programmes for individuals with ASD). Even the immediate demand on physicians' time for counselling and support of families facing potential early diagnoses is a controversy in the USA because these are generally not billable services for paediatricians. To date,

Conclusions

Life for many children and adults with ASD is improved today compared with 50 years ago. More adults with ASD can talk, read, drive, graduate from school, and live in the community—even accounting for the differences in which people would meet the diagnostic criteria now and in the past, and their respective levels of intelligence. Caregivers can be reassured that the situation has improved, and will continue to improve, for most people with ASD. We hope that research directs attention to

Search strategy and selection criteria

Initial searches were done on Aug 14, 15, and 17, 2017. Additional searches were done on Feb 21–23 and March 18–21, 2018. Searches were limited to the English language. To identify studies for this Seminar, we searched PubMed and individually searched the Cochrane database, and followed back by searching reference lists of papers cited in major journals for papers published between 2007 and 2017, using the search terms “autism behavioral treatment”, “autism diagnosis”, “autism environmental

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