Autistic spectrum disorders comprise a group of conditions within the category of childhood-onset pervasive developmental disorders (ICD-10, DSM-IV).

Patricia Howlin (UK)

Autistic spectrum disorders comprise a group of conditions within the category of childhood-onset pervasive developmental disorders (ICD-10, DSM-IV). Autistic disorders are characterized by abnormalities in three domains:

  • reciprocal social interactions
  • communication
  • restricted and repetitive patterns of behaviour or interests, with an onset in the first 3 years of life.

The term 'spectrum' is used to indicate the wide range of abilities and difficulties that may be found among individuals with these conditions. The two principal (and best defined) subgroups within the spectrum are autism and Asperger syndrome (Figures 1 and 2).

FIGURE 1: ICD-10 criteria for autism

A. Abnormal or impaired development is evident before the age of 3 years in at least one of the following areas:

1. Receptive or expressive language as used in social communication
2. The development of selective social attachments or of reciprocal social interaction
3. Functional or symbolic play.

B. A total of at least six symptoms from (1), (2), and (3) must be present, with at least two from (1) and at least one from each of (2) and (3):

1. Qualitative abnormalities in reciprocal social interaction are manifest in at least two of the following areas:

a. Failure adequately to use eye-to-eye gaze, facial expression, body posture, and gesture to regulate social interaction
b. Failure to develop (in a manner appropriate to mental age, and despite ample opportunities) peer relationships that involve a mutual sharing of interests, activities, and emotions
c. Lack of socio-economic reciprocity as shown by an impaired or deviant response to other people's emotions; or lack of modulation of behaviour according to social context; or a weak integration of social, emotional, and communicative behaviours
d. Lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g. lack of showing, bringing, or pointing out to other people objects of interest to the individual).

2. Qualitative abnormalities in communication are manifest in at least one of the following areas:

a. Delay in, or total lack of, development of spoken language that is not accompanied by an attempt to compensate through the use of gesture or mime as an alternative mode of communication (often preceded by a lack of communicative babbling)
b. Relative failure to initiate or sustain conversational interchange (at whatever level of language skills is present), in which there is reciprocal responsiveness to the communications of the other person
c. Stereotyped and repetitive use of language or idiosyncratic use of words or phrases
d. Lack of varied spontaneous make-believe or (when young) social imitative play.

3. Restricted, repetitive, and stereotyped patterns of behaviour, interests, and activities are manifest in at least one of the following areas:

a. An encompassing preoccupation with one or more stereotyped, restricted patterns of interest that are abnormal in content or focus; or one or more interests that are abnormal in their intensity and circumscribed nature though not in their content or focus
b. Apparently compulsive adherence to specific, non-functional routines or rituals
c. Stereotyped and repetitive motor mannerisms that involve either hand or finger flapping or twisting, or complex whole body movements
d. Preoccupations with part-objects or non-functional elements of play materials (such as their odour, the feel of their surface, or the noise or vibration that they generate).

FIGURE 2: Criteria for Asperger syndrome

A. Qualitative abnormalities in reciprocal social interaction - criteria as for autism. However, lack of social reciprocity is more typically manifest by an eccentric and one-sided social approach to others, rather than social and emotional indifference

B. Restricted, repetitive, and stereotyped patterns of behaviour, interests, and activities - criteria as for autism
However, motor mannerisms, preoccupations with parts of objects, rituals and marked distress at change tend to be less common than in autism. Instead, encompassing preoccupations about a circumscribed topic or interest are characteristic.

C. The disturbance causes clinically significant impairment in social, occupational or other important areas of functioning

D. There is no clinically significant general delay in language (i.e. single words by 2 years; communicative phrases by 3 years

E. There is no significant delay in cognitive development, of age-appropriate self-help skills, adaptive behaviour, and curiosity about the environment

F. Criteria are not met for another specific pervasive developmental disorder or schizophrenia

Defining autism and Asperger syndrome

The condition of autism was first recognized in the 1940s by Leo Kanner in the USA. At much the same time, however, Hans Asperger, an Austrian psychiatrist, described a very similar group of children. The main difference was that Asperger's descriptions focused on relatively high-functioning individuals, whereas Kanner's case studies included children with marked delays in language and/or severe cognitive impairments. Although Kanner's work in this area was widely published, Asperger's accounts (probably because they were written in German shortly after the end of the Second World War) received little attention. Indeed Asperger syndrome was hardly heard of until the 1980s, when Lorna Wing highlighted the fact that autistic disorders could occur not only in individuals with marked linguistic and cognitive impairments, but also in those of high IQ, and with good expressive language skills (Wing, 1981).

The diagnostic criteria for Asperger syndrome and autism are very similar. The main differences are that in Asperger syndrome there is no clinically significant delay in language, and intellectual development is relatively unimpaired. Most recent research, however, indicates that there are no qualitative differences between individuals with a diagnosis of Asperger syndrome and those with autism whose cognitive skills are within the normal range.

Autistic spectrum disorder was once considered to be a very rare condition, occurring in only around 3 to 4 per 10,000 children, but more recent epidemiological studies suggest that the total figure is much higher, with several studies indicating rates of 30-60 per 10,000 (Fombonne, 1999). Most evidence suggests that the change represents a greater awareness of autistic spectrum disorders among professionals, and improvements in diagnostic practice more generally.

Sex ratio

Like most other conditions involving language impairments, autistic disorders are far more common in males than females. The overall male:female ratio is estimated at around 4:1, although among high-functioning individuals, or those with Asperger syndrome, the figure may be closer to 10:1. The male predominance appears to be less marked among individuals with severe intellectual disabilities (possibly around 2:1).

Diagnostic assessment
Diagnosis in autism relies on the identification of a constellation of specific symptoms. Deficits in these areas must also be distinguished from deficits that may be attributable to low IQ, sensory impairments (e.g. deafness) or other developmental or psychiatric disorders. Reliable diagnosis can be achieved only on the basis of a detailed developmental history, focusing on social development, the development of communication skills, and patterns of repetitive or stereotyped behaviours and interests.

Diagnostic instruments

A number of standardized diagnostic instruments have been developed to enhance diagnostic accuracy (Figure 3). The Autism Diagnostic Interview - Revised (ADI-R; Lord et al., 1994) is among the most widely used. The Diagnostic Interview for Social and Communication Disorders (DISCO; Wing et al., 2002) also provides a structured framework for the assessment of developmental and behavioural functioning. Parental information may be supplemented by standardized observational measures such as the Autism Diagnostic Observational Schedule (ADOS; Lord et al., 1999). Various checklists are also available, including:

  • Childhood Autism Rating Scale (Schopler et al., 1986)
  • Autism Behavior Checklist (Krug et al., 1980)
  • Autism Screening Questionnaire, which is derived from the ADI-R (Berument et al., 1999).
FIGURE 3: Diagnostic instruments for autism and autism spectrum disorder

Although many different checklists and screening instruments for the identification of possible autistic spectrum disorders exist these cannot be use for clinical diagnostic purposes. A conclusive diagnosis can be reached only on the basis of a detailed developmental history. Of the very few instruments available that can be used to provide this information, the best validated are:

  • DISCO ( Diagnostic Interview for Social and Communication Disorders; Wing et al., 2002)
  • ADI (Autism Diagnostic Interview; Lord et al., 1994); this is frequently used in conjunction with the ADOS (Autism Diagnostic Observational Schedule; Lord et al., 1999)
  • A checklist derived from ADI algorithm items is also available for screening purposes (Social Communication Questionnaire, SCQ; Berument et al., 1999)
  • The DISCO and ADI cover a wide range of different behaviours (100+ items), but the focus is on communication and social deficits, and ritualistic and stereotyped behaviours. They require specialist training and take around 2 hours to complete. They can be used for diagnosis of both children and adults as long as an informant is available who has known the individual from childhood. They are suitable for high-functioning individuals (including those with Asperger syndrome) and individuals with moderate-to-severe intellectual impairments).
  • The Asperger Syndrome Diagnostic Interview (Gillberg et al., 2001) is the only diagnostic instrument developed specifically for higher-functioning individuals. It comprises 20 items, covering six different areas. Initial reliability and validity data are encouraging although the standardization sample is small.

Cognitive assessments

The diagnostic process should also ­incorporate assessments of cognitive and verbal ability. Again, a variety of different instruments is available. Psychometric tests suitable for use with children with autism include the Wechsler Scales, the Mullen Scales, the Merrill Palmer Scales and the Bayley Scales, and there is a wide choice of language tests. The Vineland Adaptive Behavior Scales (Sparrow et al., 1984) can be particularly helpful for very young or severely intellectually impaired individuals, as they assess functioning in several domains across a wide age range and are based on parental information. Generally, however, a single test will not be sufficient and a combination of different methods - observational, parent-based and standardized assessments - is needed in order to obtain a valid picture of the child's functioning across a range of different areas.

Physical examination

A comprehensive physical examination is required in order to identify any additional disorders (e.g. tuberous sclerosis or fragile-X (see also Sabaratnam 2003; pp. 29-33)) or specific neurological impairments. It is important, too, to assess vision, hearing and motor coordination, as impairments in these areas may affect children's general functioning. The presence of common comorbid conditions, such as attention deficit dis­orders, should also be investigated.

Epilepsy (see also Bernal 2003; pp.69-73) occurs in around 25% of cases, but often does not develop until the early teens, and it is important to be alert to the possibility of seizures if sudden, unexplained changes in behaviour occur. However, EEG abnormalities in autism are common, and, in the absence of other symptoms, are not in themselves an indication for anti-epileptic medication. Routine neuroimaging is unlikely to be justified, unless there are marked changes in the child's behaviour.

Differential diagnosis
A number of other conditions affecting early development may be confused with autistic spectrum disorders, including developmental language disorders, severe psychosocial deprivation, profound intellectual impairment, selective mutism, early childhood schizophrenia, Rett syndrome, childhood disintegrative disorders and Landau-Klefner syndrome. However, the onset, course, response to intervention and family background in these disorders are generally different from those found in autism (see Lord and Bailey, 2002, for review). In most cases, a detailed developmental and family history, together with careful physical, psychometric and linguistic assessments will avoid diagnostic confusion.

Theories about the causes of autism have changed markedly over the years. When Kanner first described the condition, he, and many other professionals, believed that inadequate parenting was the primary culprit. Recent increases in the numbers of children diagnosed with autism have also led to a search for possible environmental causes. However, there is no evidence that environmental factors such as vaccinations (notably the MMR vaccine), pollutants, dietary additives, and so on, are in any way responsible. Instead, it has become increasingly apparent that autism is largely a genetic disorder (Lord and Bailey, 2002). It was recognized as early as the 1970s that families with one autistic child had a greatly increased risk of having other children with autism or related disorders. Subsequent twin studies indicated very high concordance rates among monozygotic twins, and recent large-scale family studies have identified higher rates of social and communication difficulties and increased rates of circumscribed interests or obsessional and repetitive behaviours among relatives. There is also an increased risk of depressive disorders among relatives.

The pattern of inheritance in autism is unclear, but between two and 10 susceptibility genes are probably implicated, with three or four interacting loci being the most likely model. Research is now concentrating on the identification of susceptibility genes, with the focus on specific chromosomal regions, particularly 7q and 15q. Other regions of interest include 2q, 13q, 16p and 19p.

Cognitive deficits
Most children with autistic spectrum disorders, apart from those with Asperger syndrome, also have intellectual impairments. Around half of all individuals with autism have an IQ below 50. Only around 20% have an IQ in the normal range (i.e. >70). Verbal skills are generally relatively more severely impaired than non-verbal skills.
Different psychological hypotheses have been proposed to identify and explain the specific cognitive deficits underlying autistic spectrum disorders. Among the most influential of these are theories focusing on:

  • the failure to understand other people's mental states
  • deficits in understanding emotions or facial expression
  • impairments in executive function
  • a lack of central coherence.

Attentional deficits and impairments in voice recognition and visual integration have also been proposed as possible contributory factors. Findings from neurobiological studies are generally inconsistent, or contradictory. Various different abnormalities have been implicated (e.g. decreased Purkinje cell density in the cerebellum, significantly increased brain size, abnormal amyg­dala function and abnormalities in the serotonergic system). However, much of the work in this field has been conducted on very small groups of subjects, diagnostic criteria are often unclear and the impact of variables such as age, intellectual impairment or language level has rarely been taken into account.
Data from both post-mortem and neuroimaging studies suggest that autistic spectrum disorders affect the development and function of the cerebral cortex and subcortical structures, but there is considerable individual variation, and even when deficits have been found, it is unclear whether these are primary abnormalities, or whether the deficits are attributable to connectivity within and between different structures (Lord and Bailey, 2002).

Course of autism
Outcome in autism is highly dependent on individuals' general intellectual level, and also on whether or not they acquire useful language. Few children with an IQ below 70 achieve independence as adults, and many of those with an IQ in the normal range still require support in terms of living and work throughout their lives (see figure below). The early symptoms of autism are generally first recognized by parents by the second year of life, and often long before this. Nevertheless, many children do not receive a formal diagnosis until they are 4 or 5 years of age or even later. Problems of social relationships, reciprocal communication, or lack of imaginative play are generally the first symptoms of which parents are aware. Ritualistic and stereotyped behaviours may not become apparent until children are older - around 3-4 years. The preschool period (4-5 years) is often the time when autistic symptomatology is most marked. A quarter to one-third of parents report that, typically around 18-24 months and following an apparently normal period of development, their children lose speech, and sometimes social skills too.
On the whole, most children show improvements in many aspects of their development as they grow older. Some individuals do show an increase in behavioural disturbance in adolescence but this is by no means inevitable, and many actually show marked improvements in their mid to late teens.

Mental RetardationIQDegree of Impairment in adulthood
Mild50-69Fully independent for self-care and many domestic skills. May have problems with higher skills, e.g. budgeting
Moderate35-49Completely independent living seldom achieved.
Severe20-34Marked impairment
Profound<20Requires constant help and supervision

The importance of early diagnosis

Although diagnosis as early in childhood as possible is clearly desirable for many reasons, the presence of autistic features may sometimes go unrecognized if children do not show a 'classic' picture of autism. There is a particular risk of failing to diagnose autistic spectrum disorders in individuals with severe intellectual disabilities, or in those who have additional impairments (deafness, blindness, Down's syndrome, cerebral palsy, etc). Diagnosis may also be significantly delayed in children who are higher functioning, particularly those who have Asperger syndrome.

Even if autism has not been diagnosed in childhood, the presence of social and language impairments that are out of keeping with the individual's overall level of functioning, and an over-reliance on routines or stereo­typed patterns of behaviour and/or interests, should alert professionals to the possibility of an autistic disorder. Several of the diagnostic instruments initially designed for children (e.g. ADI and ADOS) can be used reliably with adults, and although there may sometimes be problems in finding an appropriate informant if parents are very elderly or no longer alive, a satisfactory developmental history can frequently be obtained from siblings or other relatives. Late diagnosis is better than no diagnosis, as it is only when an individual's needs and difficulties are correctly identified that appropriate intervention is likely to result.

Interventions for autism
Many different treatments have been suggested as being effective for individuals with autism, some of these even claiming to bring about cures or recovery from the condition. On the whole, however, these claims are rarely supported by evidence, and many treatments have never been adequately evaluated. Others - such as facilitated communication, holding therapy, auditory integration therapy or secretin injections - have been found to be no more effective than placebo, despite initial claims of almost 'miraculous' results. On the whole, structured educational programmes, combining behaviourally based strategies and developmental approaches, and utilizing visual schedules and cues rather than verbal instruction, tend to have more positive outcomes. The involvement of families in treatment, and a focus on strategies that build on the child's strengths rather than areas of specific weakness, also appear to be important. It is generally agreed that behavioural/educational/developmental programmes are a good option for children with autism, but as yet there is no evidence in support of any one particular programme, particular degree of structure or any specific degree of intensity (Howlin, 2001).


The use of medication for individuals with autism varies widely; rates are particularly high in the USA, but much less in other countries, such as the UK. While appropriate medication is clearly important for conditions that may be associated with autism, such as epilepsy or high anxiety, there are no medications that are effective for autism per se, and hence the routine use of medication, particularly for very young children should be discouraged unless there is a specific reason.

Autism in adulthood
Much of the research into the diagnosis and treatment of autistic spectrum disorders has focused on children and, despite the fact that autism is a life-long condition, the needs of adolescents and adults often seem to be neglected. For example, although autism is known to be very common among adults with severe intellectual impairments, staff in residential care units may be unaware of the presence of autistic features or of the importance of differential diagnosis for developing appropriate management and support strategies. However, the poor social and communication skills of people with autism (which are out of keeping even with their level of intellectual impairment) and their need for ritual and routine, can make it very difficult for them to cope with the demands of group living, and severe emotional and behavioural disturbance is often the result (Joyce 2003; pp.17-20). Staff recognition of their dependence on predictability and structure, of the importance of rituals or routines, and of their need for consistency (both of environment and personnel), together with acceptance of a general disinclination to take part in 'normal' social activities, can greatly help to reduce stress, anxiety and disruption. A focus on developing more effective communication by whatever means are appropriate (signs, pictures, objects or symbols) can also have a major impact on other aspects of behaviour. Even among more able adults, many individuals remain heavily dependent on others for support, and, without help, only a minority seem to cope with living fully independently, finding appropriate work, making close relationships or developing long-term sexual relationships/marriage (Howlin et al., in press).
Although access to appropriate help from an early age can be of considerable benefit, this should not detract from resources for older children and adults. As adolescence can be a time of positive change, there is a need for more widespread and effective intervention programmes at this stage. Specific interventions in adulthood, such as the provision of specially designed supported living and employment schemes, can have a major impact on later outcome.

The understanding of autistic spectrum disorders has improved significantly since autism was first described in the 1940s. It is now accepted that autistic disorders are far more common than was once thought, that they can affect individuals of all cognitive levels, and that they are, in the majority of cases, genetically determined. However, much research is still required in order to develop optimal intervention strategies, not just in childhood, but across the lifespan. Far more is still to be learned, too, about the genetic mechanisms involved, and the ways in which these affect brain development and brain function.


Any child who shows the following abnormalities of development should be considered as being at risk of having an autistic spectrum disorder:

  • No babble, pointing or other gesture by 12 months
  • No single words by 16 months
  • No 2-word spontaneous utterances (i.e. non-echoed phrases) by 24 months
  • ANY loss of language or social skills in the pre-school years

An appropriate screening instrument (e.g. the Checklist for Autism in Toddlers, or CHAT) can be used to further explore the possibility of autism. Clinical diagnosis should be made by a multidisciplinary team and at all times parents should be fully involved in the process

No cures for autism exist, but much can be done to improve outcome. Diagnosis must be followed by practical support for families and access to appropriate educational provision. Later, adequate educational, social, residential and employment support services will be needed to ensure the successful transition into adult life


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First published in Psychiatry; Volume 2:8 in August 2003 and reprinted with the kind permission of the Medicine Publishing Company.

Figure 4 is taken from Cooke LB. Aetiology of Learning Disability. Psychiatry 2003, 2:8, p.5